Throttle Block :  These motors are designed so that you can not manually start the motor (pull the rope) if the throttle is advanced much beyond the start position.  There is a dog (or interlock) lever on the top or side of the manual starter spool that drops down and engages in a ratchet that prevents the starter rope from being pulled.   These early (pre 79 motors) the ratchet notches for this neutral safety interlock are on the top of the starter spool, this interlock dog is activated by a linkage from the carburetor roller cam.

 

    Therefore it is wise to, each time you are going to start these motors to twist the throttle to the slow side, then bring it back to the start position.  The reason for this is that since there is some slack in the throttle pivot gears.  Many times, just bringing the throttle twist grip back from the fast position to the start position, the linkage has not reset it to the neutral safety position. 

 

    You can pull the starter rope handle right off the end or break the rope, if you jerk the rope hard enough and are not suspecting that the thing is locked in the safety position.

 

 

   Neutral Safety Position :   The electric start versions also have an electronic neutral safety switch, which is an inline switch between the actual starter button and the starter itself.  It is activated by the bottom of the spring detent plate that holds the shift lever in or out of gear. Occasionally if the motor will not start with the shift lever in neutral, check this switch.  The mounting bracket for this switch bolts to the side of the block below the fuel pump of the pre- 88 motors.  Loosen the bracket and the bolt holes are sloppy enough that you can usually get the switch button aligned so the bottom protrusion of the cam plate will push the button down when the shift lever is in neutral.

   Do Not Force Shifting Lever :  One thing to be aware of on these motors, is that the clutch dogs in the gearcase's transmission are rather large in relationship to some other models.  This is good in that you most likely will not experience the motor jumping out of gear because of worn clutch dogs if the linkage adjustment is not properly set.  But also at the same time, it means that you should NOT TRY TO FORCE the shift lever into a gear while the motor is NOT RUNNING.  You could very well break the shift lever, especially the newer plastic levers, or bend some of the linkage if the older metal lever.  If you HAVE to place the transmission in gear with the motor not running and the shift lever does not want to engage, try slowly pulling on the starter rope just enough to allow the clutch dogs to mesh in the gears. 

 

   Rev Limiter if in Neutral & Reverse :  On the timing plate there is a metal plate behind the actual throttle cam plate.  This is a stop lug that when the shifting lever is in neutral that the motor can not run at a high speed and possible ruin the motor, or if in reverse could create a safety issue.  This is essentially a Rev limiter.  It was not provided on the earlier motors especially probably pre 1977 that I have seen.

 

      Top Cowling Latch :  There are two different latches, both look similar, BUT the later motors where the cowling was changed to accommodate the upper rear thermostat, uses a longer shaft than those made before 1986.

 

   Motor Makes More Noise Than Normal :  The 1st, and many times not as obvious, would be to be sure the insulation is still inside the motor hood cowling.  After that then look at the following things.  (2) Has someone has repaired the lower unit, like replacing the water pump, they may have left out the exhaust baffle (note that there is no baffle in the 74-76 motors).  This is discussed in a later section.  (3) Also it could be that the upper motor mount seal/grommet is deteriorated enough that it may be letting noise, (and oily residue) leak out.  This is a rubber seal that is located between the upper rear of the pivot shaft housing and the upper exhaust housing.  At this location on the exhaust housing on each side you will see a 1/4" Phillips head screw on each side.  These screws go into the upper rubber motor mount that is located inside the housing.  The grommet is the seal between the pivot shaft & the housing.  The above 2 conditions will have more of an exhaust type sound.

    If you have a tinny type noise or rattle, then it could be  (4) The pistons may be worn and could have lots of slop in the cylinders.  This however will usually quiet down as the motor warms up and the RPM is increased.  (5) The flywheel could be loose, but this will be more of a knocking type rattle.

Also look and see if the foam insulation is still attached to the inside of the cowling.

   Prop Spins While out of Gear Using Flushing Muffs :  When the engine is running in neutral using muffs, not in the water, the driveshaft will be spinning internally in the gearcase.  The driveshaft is direct from the motor and goes through the water pump and down into the gearcase where the transmission is.  The top or input gear is called the pinion gear, it engages both the forward and reverse transmission gears simultaneously, one turning RH while the other LH.   These gears are spinning all the time the motor is running.  The prop shaft supports the sliding splined shifter dog, which when centered between the moving gears, it is is neutral, then when this shifter dog is moved either forward or rearward engaging the rotating gears, this power is transmitted to the propshaft.  Since when running, there is always oil movement inside the gearbox the movement of the gear oil in the gearbox caused by these spinning gears which is totally surrounded the gear oil even though it is not in gear and as a result the prop may slightly spin.  This is perfectly normal.

 

   Water Not Coming Out of Overboard Water Indicator Hole :   Don't panic, but VERY SOON after firing it up, if your motor is 1977 or later and you get no water spraying out the "overboard water indicator " (tell tail hole or pee hole to most boaters), get a small single strand wire and poke it in from the outside of this hole while the motor is running.  There may just be slight salt water crystals, or if it has set for a while, maybe a bug crawled up there.  If this does not get water spraying, shut it off as you may have a defective water pump impeller, which, if left running without water into the motor, could ruin the motor rather quickly.  The reason I say 1977 or later is that the 1974-1976 did not have this tell tale as we now know it, which is explained below.

   If your engine overheats and this overboard water indicator is not spraying, shut it off, look for debris plugging the intake screens on the sides of the lower unit.  Start it up again and again look for water spraying out.  If you can NOT get water coming out this hole, then SHUT IT DOWN QUICKLY.  If you get steam coming out this hole, you DO NOT have water being pumped.  Do not let it run to where the engine block is so hot you can not place your hand on the top of the block without getting burned or the paint starts to scorch, as you WILL ruin the rings. 

    If there appears to be nothing plugging the water inlet holes on the lower unit, be careful as the screen behind these holes is merely plastic.  You have checked and cleaned the tell tale hole and there still is not water showing, then in all probability the impeller is aged, worn or damaged.  One thing that will wear the impeller more than anything else is to start and run the motor without any water going thru the pump for even a few seconds.  It needs the water flowing thru it to lubricate this rubber impeller.  If run dry, the ends of the impeller can get worn/melted off, and/or the nylon impeller housing can get melted, between the impeller rubber and melted nylon, plug the water pump outlet.  This chewed up rubber can then get forced up into the upper water supply tube where it enters the block possibly blocking flow, if this rubber debris makes it into the water jackets of the motor, again possibly making a blockage that is hard to remove without about a total teardown.

   If you are running it in a barrel and get erratic water flow out this tell tale hole, you might consider pulling the motor out, then checking for debris plugging the water intake screens.  You may have to dump the water and start over with a cleaner tank.

   If all else fails to get water flowing, the one thing that will be the most likely need to replace is the water pump impeller. 

 

   For more detailed information on water pumps look at our "Lower Unit" section.    CLICK HERE
 

   Water Passage Route in the Motor :  As shown in this 1978 repair manual page shown in the LH photo below, the water is sucked into the lower unit thru the screened  holes in both sides of the gear case unit.  It goes up and into the water pump.  From there it is pumped up the supply tube to a block that is bolted to the underside of the power head.  From here it is directed into the bottom of the water jacket on the right hand side of the power head.  Some of the water can go out the overboard water indicator tube.   This overboard water indicator is commonly called the pee hole by many outboarders.  The water coming out of it will not be hot because it has not had time to circulate thru the block's water jackets.  It may be slightly warm but probably not enough for you to really tell if your put your hand in it.  It may be slightly warmer before the thermostat opens allowing more water to flow thru the motor.

   The majority of the water goes up in this water jacket, then back down and into the block.   Here it circulates around the sides of the cylinders, up and into the top of the head, thru both sides of the head and into the thermostat.  Then out the thermostat, (which should open at about 145 to 160 degrees F.)  up thru the water cover plate on the rear of the head, back out thru a passage in the head and out into the exhaust housing to be either sucked out thru the prop hub or thru the holes in the sides of the lower unit if the boat is not moving.

 
   Once the water exits the block, it flows down inside the exhaust (mid section) housing, out thru holes in the sides of the lower unit and also out the prop exhaust.  There have been changes in this flow over the years.  The early units as shown in the photo below on the left used the square exhaust pipe.  The pre 1981  15 hp also used the square pipe. 

   Approximately 1981 saw usage of the round tuned exhaust pipe for all the later 15 hp motors.  And later nearing 1990 this tuned pipe was used on all 9.9 and 15 hp motors.   You will note that the early square pipes did not have a separate 3/8" copper tube exhausting the flow farther down inside the actual exhaust housing, but only let it spill out at the base of the motor inside the housing.

   As shown on the right of the photo below, the newer motors used this round, tuned exhaust pipe, they also have added a short 3/8" copper tube diverting the exhaust water farther down inside the exhaust housing.

   Not shown below is an last exhaust pipe, used starting approximately 1986 that was very close in appearance to the round long one but only about 6" in overall length.  It used the short 3/8" copper tube only, but about 1/2 the length shown on the RH one below.

   In the left photo below, notice the deteriorated rubber grommet protruding out the bottom of the exhaust pipe.   For an explanation of possible water tube grommets deteriorating where they attach to these exhaust tubes, possibly causing water blockage CLICK HERE for a link to my water circulation problems article.

 

      The question has arisen, will the later round exhaust fit/replace the older square version without any alteration?   You will note in the RH photo above, the older square tube is about 1/2" longer than the round tube.    The round tube does NOT have a gasket at the bottom like the square tube does.  Apparently the design for a sealed exhaust was not needed.   Looking at a parts list for both the 9.9 and 15hp gearcases in those years, they are the same, which I expected as it would have been expensive to make a new 15hp only gearcase. 

 

   No Overboard Water Indicator as we Know it, for the First 3 Years of Production :  The water simply was pumped thru the motor, then was exhausted out the bottom of the powerhead into a split section in the exhaust housing.   There is a rear chamber in the exhaust housing that is only open on the bottom, slightly below the one 3/8" blubber hole on the outer rear of the housing.   This system was common to all the earlier OMC engines prior to these years and was carried over into this series of motors thru 1976.  
 

   With this older system it is can be hard for the inexperienced to tell whether your water pump was really working until the thermostat opens allowing hot exhaust water out the blubber hole, as as compared to a motor that uses the newer tell tale system.   After the thermostat opens, you get lots of hot water and some exhaust gasses out this 3/8" blubber hole.   The one thing I have found however is that at an idle there is not much water blubbering out this hole.   If you are not certain, if the motor runs and the block does get so hot that you can not hold your hand on it for about 1/2 a minute, or the paint on the upper rear block starts to burn, the water pump is bad and needs to be  replaced.

   On the pre 77 motors the blubber hole exhaust chamber is open into the 6 holes on the rear sides of the lower unit, forcing the water out the blubber hole or being sucked out the lower holes when in the water.   Later motors used a exhaust baffle plate (with numerous holes in it) at the lower end of this chamber, this apparently allowed for better breathing of the newer motors since the overboard water indicator pulled water off at a different location.

   Back pressure from the exhaust inside the total housing forces some of the outlet water up which it pushes a combination of exhaust gasses and a watery mix out this upper indicator hole.   When running right and with the boat in the water, (which places back pressure on the exhaust) there should be considerable water mixed with some exhaust blowing out this hole.   If you however run it using muffs, you will get very little spray water out this same top exhaust relief hole.    Without exhaust back pressure, all the water that is exhausted goes out the bottom then out thru the prop.

   After the motor warms up, if you can lay your fingers on the flat place on the top of the block at idle RPMs and hold them there for about a minute without a great discomfort to them, (as the thermostat opens at about 150 degrees) if your engine is running about right.

   From looking at parts and service manuals for 1974 thru 1976 it is my observation that the "New Overboard Water Indicator" was not introduced in this series until possibly late 1976 or early 1977.  I have one 74 powerhead that has no provision for any overboard water indicator of any kind, but I have another with a model number suffix of G, it has a modified water jacket that has an 1/8" pipe fitting tapped into the upper section.  It also has some sort of a formed plastic spacer that goes over this section and the tapped Ell 1/8" pipe fitting going thru both.   This main water jacket area is thin and possibly the plastic was designed to help eliminate leakage.  This threaded hole is located in the upper mid part of the water jacket.  This location could only have been used for a manual start motor as it would have been in the way of the wire connection terminal block of an electric start version.  

   My assumption is that this is was NOT a factory modification, but an owner or more likely a dealer modification.  Then I have another same year motor with a prefix S, that has a raised threaded boss like the later versions on the lower section of the water jacket.  The simple method of converting would be to replace the outer water jacket with a newer one with the pipe thread outlet and drill a 1/2" hole in the rear of the lower cowling with a rubber tube connecting them.  The photo below shows the normal outlet position of this modified jacket.  All the 1977 motors that I have seen do have this Overboard Water Indicator.

   I would recommend anyone having one of these older motors without the "Pee Hole" to convert it to the newer style, as the is no doubt then if the water pump is working or not.   However taking a page out of the newer motors design, it may be best to consider placing the outlet Ell nearer the top of the water jacket cover.   The reason here is threefold in that (#1) it is easier to rout the hose, plus (#2) it may eliminate a vapor lock in the upper water passage, that could slow down the initial water passage into the block.   And (#3) this sideplate CAN NOT be taken off the powerhead UNLESS the powerhead is removed from the midsection because you can not get to the lower front bolt under the rubber motor mount.

 

 

   This hole can be drilled and tapped at the upper location while this sideplate is still on the motor.  I would however place some chassis grease on the drill to pick up most of the chips when drilling.  Also do the same on the tap when tapping.   I would use a starter drill of about 3/16", then finish the hole with a R drill (.339 dia.) or a 11/32" (.344 dia.) drill and tap to a 1/8" pipe thread.  This material is thin, (less than 1/8" thick), there is a cavity behind it that gives enough room to drill and tap, BUT don't tap it deep (only enough to get a few threads in the jacket) as pipe threads are tapered and you need to have this fitting tight, pointing down and rearward when finished.   If you don't get it deep (large) enough, you can always tap it deeper.  It is rather hard to make it smaller if you find you made it to deep/large.

   Since pipe threads are tapered, tap it in only about 1/8"to start with and then try the fitting.  If you happen to go too deep it may bottom out inside and you would then have to shorten the Ell threads of the fitting.  A 1/8" pipe Ell with a 3/16" barbed hose fitting is what you need.  The OMC Ells #321886 are made of Nylon, and is recommended as they are more forgiving if you need to tighten more. Apply some non-hardening gasket sealer to the threads.  If you do need to tighten it in more, you may have to file off some of the metal or Nylon off the threaded screw boss just in front as the Ell barbed fitting may hit it while rotating and you can't get it rotated enough.

   One problem with this upper location is that you can not use this location if the motor is a electric start version because it would interfere with the electrical junction block from the power source, unless the upper junction block screw was removed & the junction block was rotated downward slightly & then only use the rear screw to retain this junction block.  Not really a good thing.

   In the photo on the left below, is an you can see the actual modified Overboard Water Indicator using a OMC Ell.  The bright aluminum protrusion at the bottom of the cowling is simply a aluminum rod with a .085 dia. hole and the barbed end lathe turned to just have a snug fit inside.  The tubing is clear vinyl  3/16" ID, X 5/16" OD (just the same size as the hole is drilled into the cowling).  However I found that if there is a vapor lock inside the jacket, creating a blockage, this tubing can become so hot that it may rupture.  So I have now went to rubber windshield wiper tubing instead as seen in the RH photo below.  An O-Ring of a tight fit is slid onto the tubing to form a stop for the tube's protrusion out of the cowling.  The beauty of this is that IF the outlet hole becomes plugged, this tubing is flexible enough to be pulled upward out of the hole and easily cleaned.

   In the photos below you will see the differences between the early non tell tale hole and later water jackets.  On the right at the red arrow you can see the threaded hole for the water outlet Ell of the newer jacket.  You will also notice the lower right bolt hole, which is the one you can not get to without the powerhead removed.

This outward hole in the 1977 and later plastic overboard water indicator is small enough (.085 dia.) which is about the size of a wooden matchstick, small enough as to not draw off a high volume of water.  From there, the water is routed up the rear of this jacket, over the top, down and into the block.  The flow then splits, then goes on each side of the cylinders and out the top into the water jacket of the head.  The flow splits again and circulates around the inside of the head’s water jacket, then out the bottom to the thermostat.  It then goes out the thermostat, when the proper temperature is reached, up to the top and then back down the thermostat water jacket, into the lower head, then into the lower block, out thru the exhaust housing’s divided section, out the baffle, then out thru the 4 holes on each rear side of the gear case above the cavitation plate.  These holes are there so that when the motor is being run in the water without being in gear, the backpressure is vented out thru these holes.  When the motor is in gear, the prop is turning and the boat is moving forward, this backpressure is sucked out thru the center of the prop.

   Even after the new overboard water indicator (tell tale) was implemented, the old vent mist holes were left in the upper housing.  They may have changed from one to two and also in size, but they still are there.   The later ones (1987) have a plastic cover that acts as somewhat as a muffler.   They are there yet probably as simply a relief hole so internal exhaust pressure will not build up inside the upper housing. 

   This indicator water, when the motor is running should be not that much warmer than the water the boat is setting in, as it is just an indicator that the water pump is functioning and is exhausted from the engine before it has a chance to warm up.  So, if you DO NOT see any water coming from this overboard water indicator hole, AND you are sure the hole, or tube leading to it is NOT PLUGGED, then you most likely do not have any water circulating in the motor. With the motor running for a period of time enough to warm it up and the engine is to hot to hold your hand on for any time on the block's top, there is NO WATER  going thru the motor.  If not, or a minimal amount of water is being pumped, you may see steam coming out the overboard water indicator hole. AGAIN, NOT A GOOD THING.  The engine should be warm enough that you can place your hand on the main block for a period of time without being unbearably hot.  If it is hot, or the paint starts to burn, it is too hot, shut it down immediately and hope you have not ruined the rings or scored the pistons/cylinder walls.

   Later in 1987 or so, the factory changed the the overboard water Ell by moving it to the bottom of that side plate, complicating it's removal to clean without pulling the powerhead off the midsection.   I have seen some with the Ell pointing up and others with it pointing down.   For the upward pointing ones, the tube was made longer, re-routed up and around the outside of the powerpack and motor mount.  This greatly improves an access to this tube for checking if there is any question as to if the water pump is functioning.  With the tube in this position, you can, if careful, pull the tube off the outlet plastic fitting to get a better idea of where the obstruction is if there is one.    I have a 1989, which the Ell is pointing down, complicating it's removal to clean without pulling the powerhead off the midsection.

 

   Many times the blockage will be at the outlet, but the other location would be at the Ell in the water jacket on the motor.   With the motor assembled in a running situation this Ell is about impossible to get at.  With this rerouted tubing, you can apply compressed air to the tube, blowing any internal debris away from the internal blockage area.   Sure this may not be the cure all, but it can give you an indication as to where the problem lies.  Heck you may even have to blow it out a few times before whatever was blocking the hole gets broken up and flushed out.  But this is a lot easier than burning up a motor, or having to tear the powerhead off just to clean a dirtball. 

   It has been observed that before the motor gets warm and the thermostat opens, the overboard water indicator hole spews more of a volume of water than after the thermostat opens.  Since the thermostat is near the last spot in the water cooling system, when the thermostat opens allowing a flow of the water to pass out of the motor.  This then lowers the pressure slightly at the overboard water indicator hole.

   I have come up with a new tell tale unit that makes a lot of sense.   Here I use the rubber grommet off a 1992 motor that fits in the lower cowling, I then lathe turn a aluminum or brass nozzle that just fits this grommet and extends out about 3/8".   I make the upper end the size that it just is a snug fit about 1/2" into the overboard exhaust hose.  This hose and nozzle is then just lightly pushed into the grommet with the nozzle being the pee hole exit.  In use, if the hole gets plugged with debris from the motors internal water jacket, all I have to do is pull this hose up and out of the grommet as indicated in the RH picture, pull the nozzle out of the hose, freeing any debris.  No wire poking in the hole that just pushes things back into the hose.   This is just held in place by friction at the grommet and on the nozzle from the hose.   You might have to replace the hose with a more flexible one if yours is hard.

   Note, DO NOT use light clear plastic tubing (sure it makes sharp bends easier, but) for the conduit for connecting to the water jacket to the nozzle.  I did this once where the outlet plugged up, and the water got hot enough (no circulation) that it heated the plastic enough that it swelled up, blew a hole in the now thinner walls, spraying hot water all over the engine.  Rather bad it you are running in salt water.

 

   Replacing the Thermostat :  It is advisable if you are having water pumping problems to also take a look at the thermostat, since if the water pump impeller had gotten any of the vanes worn off, this is a location that this chewed up vane rubber material can collect and plug things up.  If your motor is older, you may consider replacing the thermostat anyway.   The word is that the newer thermostats are constructed of a stainless steel, a better material if exposed to salt water and operate better than many of the older ones.
 

 

   The thermostats are supposed to open at about 160 degrees F.  which will allow the head to heat up just above the point that you will want to hold your hand on it for much more than maybe 10 seconds.  If it gets hot enough that you can smell burning paint, shut it off as the motor is too hot.

   On the motors from 1974 and before 1986 this thermostat is located in the lower portion of the outside rear water cover, which is bolted onto the rear of the head. The thermostat is in the very bottom of this cover. The cover can be removed from the motor without removal of the power head.  BUT you will have to remove the rear cover latch to allow enough room to access the lower RH cover bolt to be able to remove this cover.

    This can be a little tricky in that you need to keep unscrewing the latch screw (1 flat at a time) from the inside, pull the latch lever rearward so that the screw is totally unscrewed allowing the lever to be retracted rearward out of it's hole.   Once you get it about 1/2 unscrewed you can hold onto the bolt head and unscrew the latch lever.  Now the inner actual latch can be pulled out after it falls off the screw, which then the screw is free allowing the thermostat cover to be removed.

    Now when getting the head ready to go back on.  INSTALL the two lower head bolts in the head otherwise you do not have enough room to get them in the head bolt holes if you start bolting the upper ones in first.

    The problem for reassembly of the cowling latch is usually that the wafer washer is hard to get aligned over the lever shaft AND then get the latch aligned with the flats coinciding with the flats on the shaft all at the same time.   I have found it easier to get the bolt and flat washer angled in place, then have someone with skinny fingers place the latch and wafer washer over the bolt while the bolt is then poked rearward but not out the hole.   At the same time push the lever/shaft in the hole, trying to align everything.   Rotate the lever as much as possible trying to get at least one thread started.   Don't worry about the placement of the latch until you get the bolt pretty well tightened, but still allowing clearance to slide it onto the flats.   Once you have the threads going, you can rotate the lever and at the same time tighten the bolt head with a wrench, speeding up the process.

   A Better Way   Make up a piece of 1/4 X 20 all-thread, screw it all the way in until it bottoms out, calculate how much more you need to secure the latch plus a nut of the same size.   It is a lot easier (but still a challenge) to start the nut on this stud than trying to align a bolt, wafer washer, latch and washer.   LocTite the threads into the latch lever, line up washer and latch on the inside, push the lever with the all-thread bolt in from outside and place a nut on the end of the threads, tighten the nut, and you have saved a lot of frustration.

   Before you get this far, you might just want to also install another piece of 1/4" X 20 all-thread in the head that holds the bottom RH cover plate.  Again for convenience and avoiding frustration as seen in the photo below, otherwise you also have to have the bottom RH bolt inserted into the thermostat cover before you slide it into place as there is not enough room to do it once the cover is in place. 

   There was also a change in the head and the newer cover has scallops cut (as shown below in center) to allow better access to both spark plugs in about 1977, with the cover gasket also being changed at this time because the cover went from 7 bolts to 8 bolts holding it on.   This new head was changed for better fuel burning to help eliminate fouled plugs found on the 74-76 motors when trolling.  It had wishbone shaped wedges near the plugs in the combustion chambers.  This was supposedly for revised water circulation which was supposed to keep both cylinders more even in temperature and reduced plug fouling especially on the bottom plug.  The scalloped spark plug locations helped in installing the spark plugs.

   The later motors, at about mid 1987 have a different head as mentioned and shown above.  The water jacket of the head that the thermostat is housed in, was changed to place the thermostat on the upper rear, making it a lot easier to access the thermostat.  This thermostat is all together different, in that is is encapsulated inside a sealed plastic unit.  And the thermostat plate gasket is simply a neoprene O-Ring.  When re-installing the thermostat on these, it might be wise to add some anti-seize to the cover threads.

 

   These newer motors from 1987 on when replacing the thermostat, there is a base seal under the stat, pressed into the head.  This thermostat  has a rubber ring bonded to a stainless steel base that when pressed into the head is so tight that if you get a stat kit with the seal, many times you can peel the rubber off the base and not even know that the base is still there.  The new seal will not fit because part of the old one is still in the head.   This seal is pressed in rather tight, so unless the rubber seal is bad, it is recommended not to remove it, but just take care of the thermostat.

 

   As seen in the photos below, you can see the arrangement of these parts with the thermostat and spring in place, and with them removed.  In the RH photo below notice the bevel on the left (forward) end, which mates into a rubber seal pressed that is into the head.

   One suggestion, is that since these post 87 motors are so easy to remove the thermostat, is to occasionally remove it to check for debris that has accumulated inside it.  The photo of thermostat on the right above has some small fir needles and alder leaves that did not make it through.  And a dose of compressed air and flushing did not solve this one that was stuck open.  This one was so bad that after I installed a new thermostat, I dissected the old one, it had the small internal shaft seized so tight inside the outer tube that no way could it operate.  Maybe now I will occasionally pull the cover and squirts some WD-40 on this small shaft. 

    I have comparing both the old head bolt pattern for both the 74-76 and the 77-86 with newer 87 style heads.   The newer head with the top mounted thermostat could be interchanged with the older head.   If you make the conversion to the newer head, the coils may be slightly different configuration, but they can be made to function as the mounting bolts are all the same locations.  However you will also have to use the corresponding later upper cowling as with the post 87 head AND thermostat location, the old cowling does not have enough room to latch down.

    Do not run the motor without the thermostat.  The motor needs to come up to temperature in order for the spark plugs to to run hot enough to burn any excess mixed gas/oil so it will not foul, short out and make the motor run bad or die.   It also needs to burn the oil that may accumulate in the piston ring grooves so they do not become seized in the grooves which create more problems.  However if the motor is used in saltwater, be sure to flush it after usage as if there is salt buildup inside the motor, it WILL be at the thermostat area and if enough is there it will restrict the motor from cooling as the thermostat will become stuck shut blocking any flow of water as evidenced by the photos a bit farther down in this article.

 

 

  One other thing, that after the thermostat was relocated to the top of the head, the upper cowling had to be reshaped making it longer at the rear to accommodate the new thermostat.  That is when they put a bevel on these cowlings.

 

    Possible Water Circulation Problems :   One cause could possibly be is that if the motor has been run in very muddy or debris filled water, and that some of the internal water passages could be plugged.  Even if you happened to run aground on a sandbar.  If this is the case, the restriction or blockage will usually be in the RH water jacket sideplate, (the first water jacket the water is pumped thru).  However you can not take this plate off to check, and clean the passages unless you remove the powerhead because the motor mount is in the way of ONE bolt underneath it.  The other area of restriction could be in the head, at the thermostat.

   If you are absolutely sure that the water pump is good, and the passages are clear, and you are also as sure that what you are seeing is exhaust exiting from the thermostat area, the following could be the cause. 

   One thing you should do if no water is coming out, is to poke a wire or weed eater cord up in the overboard indicator to dislodge any debris that may be there.  I have seen small bugs build nests in there.  If this does not do it, then possibly there is a blockage at the plastic elbow on the other end of the tube that goes into the water jacket on the motor.  The way things are put together, you can not get to the lower front bolt to remove this cover plate without complete powerhead removal.   Here may be the time to use compressed air to blow in from the water exit, this however may just prolong the issue if what was blocking gets pushed back again.

 

   For a link to the Water Circulation Article describing this in detail, CLICK HERE.   Go down to #6 in this article.    Another thing to look at is either the head gasket or the sealing area surfaces between the cylinder head and the block have become faulty. This would allow the combustion, the power from the explosion in a cylinder to escape across to the water jacket area, forcing its way down against the water pressure that's attempting to travel upwards. This results in a stalemate obviously and the engine overheats.  I'd suggest that you remove the cylinder head and inspect that area.

   The pictures below are from the 1974 motor described in Story #1 of my overview article.  Note -- in neither picture can you see clear thru the area on the bottom, and into the thermostat location.    This area has to be clear for the water to pass thru and cool the motor.   The water pump can be going it's job, but if the passages are blocked it is the same as if there water pump was not functioning.     

     

   You may have some other problems other than the obvious of a bad water pump impeller, but the above listings are the most common.   For more information on water circulation problems CLICK HERE

 

   In the photo below, you will see the inner and outer exhaust water covers.  The main water enters the engine from the lower right blue arrow , the secondary from the upper blue arrow.  It also enters from the red arrows on the right to even the cooling.  From there it goes around the other passages in the outer cover, exiting at the green arrow hole along with the left hand red arrow holes.  Then it enters the block through a small hole in the water jacket which would be near the upper left of the inner cover.

   This motor had been "repaired" by some shade tree mechanic that most of the branches and leaves were missing, giving him a fried  brain.  These factory gaskets have a self sealant on them.  However this guy, (probably was trying to use the old gaskets) applied enough Permatex gasket sealer on both sides to 90% block three of these holes, completely block the other two, leaving only one open.

   This situation may well contribute to a poorly performing motor, becoming hot in one side of the block and restricting flow to the rest.

   Fuel Pump Repair/Replace :  Typically this size of fuel pumps were used on about all the 2 cylinder engines in the same year range, from the 2.5hp up to the 55hp models.  The fuel pump is normally pretty trouble free device.  These pumps are activated by vacuum created below the pistons of the motor thru a hole into the inside the motor’s side plate that leads into the crankcase.  If a problem occurs, check the 2 hold down machine screws and the neoprene gasket under the fuel pump.  There is also a filter screen on the outside of the fuel pump.  

   The older pumps are basically the same as the new ones with the exception that the new bodies have 2 external tabs, that align with the diaphragm tabs and other gaskets to help make it easier to assemble the parts correctly.   The repair kits do not even list a kit before 1982.  You however can use the new kits in the older pumps if you are careful and replace the new parts just as the older parts came out.  Price on a rebuild kit is about $12.00.  There are 2 spring activated check valves, one on the suction and the other on the outlet.  There is also a small spring and plunger inside all this, making it slightly hard to keep everything in the proper locations while making the final assembly.  It is suggested that you use the 2 longer attaching screws as guides in from the back side to align things before the final assembly.  Do not be surprised that you may have to do back and reassemble it a time or two before you get it right.  One word of caution, do your repairs on a clean LARGE uncluttered table as the parts are small which may tend to crawl off and hide.  Also read and understand the instructions that come with the kit.  For a link to the fuel pump article CLICK HERE.

    The newer fuel pumps are different, from about mid 1987 on, but the old type fuel pump appear to be still used for the rope starter versions while the new type was used on the electric starter models.  The new type was moved to the LH side of the power head.  A 5/16" NF threaded hole was tapped into the original fuel pump vacuum location with a hose fitting allowing the hose to be rerouted behind the head to where the new pump is located just in front of the electric starter.  This new fuel pump was not designed specifically for this motor, as it was also being used on almost all of the larger motors of this date and on.

 

   Fuel Tank Problems :  These engines use a single line fuel tank hose and a fuel pump that is a suction type, which has been used on OMC since 1959, therefore DEPENDING on the version of the tank, the vent on the top of the tank HAS to be cracked open.  Some OMC tanks have an internal vent in the cap.   All (that I know of) aftermarket tanks do not and need to be vented by the screw on top of the cap.

 

     The hose couplings are the same on the tank as on the motor, so be sure you attach the hose properly, allowing the fuel to flow toward the motor.  The primer bulb has 2 check valve balls inside of it making the gas flow only one direction and there are usually arrows on the bulb indicating the direction of flow.  The arrow needs to point toward the motor.  If you find where the primer bulb will not pump up and stay hard prior to starting, there is probably a air leak in the fuel line or fittings on the tank.   Also, if at  times and the requirement will be to pump the bulb occasionally to keep the motor running, this is usually an indication of a fuel line leak, as it is sucking air somewhere.  It can even be a split suction line inside the tank.   Assuming that there's no air leaks or restrictions between the primer bulb and the fuel supply, then the problem could be caused by faulty valves in the primer bulb. To check this out, with the engine running, hold the bulb in a vertical position, with the upper hose being the one that leads to the engine. This vertical position is best in order to have the internal valves work properly.  If that doesn't bring an improvement, it is strongly suggested purchasing a new primer bulb assy. 

   Another situation is when the boat and motor is setting for a while, if you leave your fuel line attached to both the motor and the portable tanks full, WITH THE TANK VENT CLOSED, then when the weather gets warm, the pressure inside the tank will force gas up into and past the carburetor float then into the engine.  This excess gas will then leak out and down the exhaust housing, mixing with carbon inside this housing which will cause a black oily residue to ooze out of the motor.

    There can at times be other problems related to heat and gas vaporizing in warm weather.  There is the possibility it could actually pop the internal ball valves out of one end or the other of the fuel connectors, plus possible internal damage to the fuel line bulb.  Some boaters when leaving the motor set for a while, will push the ball in with a pencil to relieve the internal pressure on the fuel line.  It is best to get into the habit of unplugging the fuel lines from both the tank and the motor when not being used.

    When the engine is running, the fuel primer bulb should NOT be firm, as it was when you primed it.  When the engine is running, the bulb is usually laying in somewhat of a horizontal position, the fuel simply flows through it (more or less about half full).  If you find that the bulb is hard, the fuel valve inside the bulb probably has come apart and the inner portion fallen out, turned itself around, and or then pulled back inside the valve housing.  In effect this is shutting off the fuel supply.  Also many times the primer bulb can, over time, get hard enough that it is hard to prime the engine.  If this is so, it is probably about time to replace the whole fuel line assembly as the lines usually then also be getting hard.

    Some of the older Tempo plastic gas tanks with unitized fuel gage and fuel pickup with the rectangular clear plastic viewing dome, may WARP after a period of time and the neoprene gasket underneath does not seal anymore. If the tank is exposed to the elements, when it rains, the water runs in on the top of the tank around this seal where it collects.  This can be checked by simply tipping a full tank, if gasoline leaks out around the gauge/outlet, water can surely leak in.  As a layman's fix, you can usually remove the O-ring and use silicone sealer between the tank and this bolt on flange.

    In many metropolitan areas, disposal of contaminated gasoline cost upwards to $3.50  a gallon.  I think I could figure out a method of filtering, or straining it and then reusing it in a lawnmower or something.

    If the gas tank has been setting for some time with fuel in it and the fuel has somewhat evaporated or turned to a brown jellied mass, one method I have used to clean the internal parts of the tank, is to put some paint stripper along with some pea gravel or small rocks inside the tank.  Let it set for a day or two, then shake, twist and turn the tank repeatedly.  The rocks will help break things loose, where the paint thinner helps loosen the old gas.  You might have to do this numerous times changing the paint stripper, depending on the severity of the contamination.  When it is fairly clean, dump the contents and replace the paint stripper with rubbing alcohol.  Repeat until the tank in clean. The rubbing alcohol is cheap and will also mix with any water that may have remained in the tank, so the water is removed at the same time.  The alcohol also evaporates, so you do not have a disposal problem, which you would if you used gas to clean the tank. 
 

   Fuel Octane Rating :   As for fuel, briefly the gas should be non-leaded, with a minimum of 87 octane rating which now was originally called gasohol, now it is Ethanol.  This 10% alcohol additive may soften some of the older fuel lines, fuel pump diaphragm, carburetor gaskets and not be compatible with some current outboard motor needs.   The alcohol in the fuel will within a couple of months separate from the gasoline and will by it's nature attract water.  This is not good in a carburetor especially if it sets for a while.

    The reason for mixing oil into the gasoline is that since these engines are 2 cycle, (sometimes called 2 stroke) there needs to be oil mixed into the gas to lubricate the internal parts (piston, crankshaft & bearings) of the engine, as there is no crankcase oil reservoir or oil pump as in the 4 stoke engines.

    Less oil than recommended in the fuel makes the engine run leaner and warmer (less power, causes detonation, overheating, but more important, could cause the motor to get so hot that it could seize the piston inside the cylinder walls), more oil makes the engine run rich and fowls plugs (less power too), forms carbon deposits and friction can increase caused by the carbon builds up, so more heat is also made.  Therefore a happy medium needs to be achieved.

   You will see considerable discussion from time to time of this fuel ratio mix on at least one of the major boating forums.  There are some that seem to be emphatic about sticking with antiquated factory recommendations even though the oil quality has dramatically increased during the last 30 years.  It seems that if you take a page from the new automobile manufacturers concerning recommended oil changes and apply it to outboard motors there should be a parallel where the old days it was recommended to change oil every 2500 or 3000 miles, now that has moved up to 5000 or 6000 miles.  This change pretty well has to do with better engine construction, the use of newer AND better oils. 

 

   Black or Gray Oil Coming Out of Upper Exhaust Vent &/or Lower Unit Holes :  Many of these motors are basically used as a secondary motor, and usually then as a trolling motor, which are ran for considerable length of time at a lower RPM.  The fuel oil mixture ratio of 50-1 is probably too rich for this type of usage. The black oil that seeps out of the motor is just unburned oil from the gas mixture.  The black color is coming from the carbon created during the pistons firing situation and is accumulated unburned inside the exhaust housing.  When the motor sets for a while the excess unburned oil in the fuel is mixing with and softening up the carbon, creating the black oozing oil.  You can reduce the amount somewhat by properly adjusting the carburetor idle jet to it's leanest position, also where the motor runs best at an idle. 

   This black or gray oozing oil could be also because of a stuck open thermostat which would not allow the motor to warm up.  However thermostats that get stuck usually do it in the closed position, so a bad thermostat is usually not the cause of this condition.

   Or, it could be a 6 gallon tank that the fuel line is still attached to the motor during storage while the outside ambient temperature is high enough to expand the fuel inside the tank to where the gas is forced into the carburetor and IF the needle valve is leaking, it will force fuel into the engine and out the exhaust which mixes with the exhaust carbon, then leaches out as BLACK oil out the prop's exhaust.  

   If you are getting a thick creamy gray oil oozing out the prop hub, it is essentially the same as above except the inside of the housing may have less carbon build up, therefore the color will be lighter.   It is the same thing as described above, but possibly from a new or rebuilt motor that may not have been run much for some time and there is not a lot of carbon inside the exhaust housing.   If there is minimal carbon built up from previous runnings, the oil will be the thick creamy light gray color that has a lot of water mixed in it.   This could also be caused by the converging ring (#332395) is missing on the prop.  This plastic ring facilitates a suction from the outside of the prop when the motor is running at a slow speed to help suck more of the exhaust gasses away from the "thru the prop exhaust" when idling in neutral or running slow.

   This oil seepage may not be evident until a day or even a week after usage, then will seep out up to a couple of months later.  Most repair shops just recommend that for most boaters to then simply live with the idea that you may have to wipe it down after each usage. 

    You could also see this oil seeping out of the front lower unit water drain hole.

    It is observed that if these motors are used on a smaller boat as the only propulsion, and act as a "get there" motor and also as a trolling motor, this black residue is considerably less to almost non-existent because the motor gets hotter because of the faster RPM, where the motor has a chance to warm up, thereby "burning" some of this excess oil.

    Also if the engine was winterized with fogging oil then you would expect to see oil coming out of the exhaust because this would soften any carbony buildup in the exhaust system.   If it smells like gas  =  unburnt 2 stroke oil.   However if it smells of rotten eggs  = Lower unit oil.

    This many times may be confused with the lower unit oil leaking because of the color and location of the oil coming out.   Another reason as to this also happening is as explained above under the Converging Ring on the prop, is if this ring is missing it can hurt by not creating enough suction to pull the oily residue out of the exhaust housing at low speeds.

   Akin to the above situation, where spark plugs have continually become fouled, I have been experimenting with using 2 gas tanks for the last eight years now and for me, I am happy with the idea.  One, a 3 gal. tank, mixed at 100-1 with full synthetic oil and it is used  ONLY FOR TROLLING, the other is the 12 gal. main 50-1 tank also used for my 70hp outboard jet on the same boat.  Again, I am using the 100-1 synthetic only for trolling with the 9.9.  If and when I need to run with this 9.9 motor faster, I simply switch to the larger 50-1 tank.  However the winter of 2007/2008 in an emergency flooding situation, where I was rescuing a lady and her son who were stranded in her house with the water was still coming up fast, my main 70 hp jet water intake had become plugged with floating grass or hay, making it useless.  It was getting dark and we were caught is a strong very swift current pushing me broadside to a fence, I did not have time to change the fuel tanks as I was broadside to the current, with the 9.9 then my only source of power then.  I ran this motor at full throttle during the last half of this rescue mission for probably 20 minutes before I got to dry ground and offloaded the passengers.  As of 2013, I am still using this motor with no apparent harm.  But I was using the FULL SYNTHETIC oil mix.

   I got the above idea from the newer VRO oil injection motors.  This VRO abbreviation stands for Variable Ratio Oil injection.   The larger motors using it (not the 9.9 or 15hp however) electronically sense the different RPMs then automatically adjusted the oil injected ratio.   They put out a 50-1 ratio at high speed and a 100-1 at slow speeds.  Recently the motor manufacturers have gotten away from this VRO system and went to a direct constant ratio pump.  This apparently is because with the VRO on a large motor with multiple carburetors, if you are idling, or trolling at the lower ratio fuel mix, so you decide to pick up and run, the carburetors still has the bowl full of that low ratio mix, the engine will then be UNDER lubricated until fresh richer fuel is drawn into the carburetor.

    I have kept track of the run time at trolling with this 100-1 ratio with one particular motor over a four year period and can account for 43+ hours of only trolling, with only one a sputter, all it took to clear that up was to speed the motor up until the spark plug became un-fouled.  Then 4 hours later, back home I changed the plugs before the next run.   In 2009, I switched over to using a 75-1 ratio of a semi-synthetic oil mix with the idea of not having to worry about changing tanks, but I do get the black oily residue as seen in the photo above, so possibly back to the 100-1 full synthetic ratio for all my running.

   You will see responses on some of the major outboard motor forums being very adamant to not deviate from the factory 50-1 ratio.  I realize that many of these knowledgeable persons, (many who may be old line mechanics) who may have seen blown engines in the past which may have been attributed to poor oiling.  However oils have changed dramatically even in the past 10 years.  Others on these forums expressing their concern may be just repeating what someone else has said.  And you have to consider that anyone who posts on a public forum does not want to stick their neck out, make a recommendation only to be chastised if the results turn out negative for whatever reason.  That is the way of life these days where liability's head pokes itself out.  That said, I have done the tests ON MY MOTORS for a number of years and you have read the results above.  I am happy with what I now use, but if your situation is different, then make your own decision.

    I many times use the boat in bays which are somewhat salt water, initially I used to switch tanks to the 50-1, when I use the muffs to flush out the trolling motor at the end of the day.  The thought here is to use the richer gas to leave a better oily film inside the motor when it is stored until next time.  I now think that the full synthetic oil is so much better, that I don't bother changing, however when flushing, under these conditions, I do NOT KILL the motor with the kill button, but choke it to kill it.  This will tend to also increase the fuel/oil inside the motor if I do let it set for a while because where I live, as I normally do not fog my engines for winter storage.

 

   Shifting Problems :  Any time you may have a shifting problem, do not immediately question the gearbox, ESPECIALLY if you happen to be using a motor that is hooked up to remote controls.  The cables can become seized internally, or possibly stretched, out of adjustment or even become unhooked from the motor.  There are adjustments of the cables at the throttle/shift control ends.

 

As a test, if you do have remote controls, disconnect them from the motor and try shifting the motor manually at the motor as a test as explained above

   Transmission Stuck in Neutral :   Do Not Force Shifting Lever IF Motor Not Running.  The above heading is wrong, but that is what many owners suspect.  One thing to be aware of on these motors, is that these transmissions (gearboxes) ARE NO SYCROMESHED LIKE VEHICLES.  The clutch dogs in the gearcase's transmission are rather large in relationship to some other models.  This is good in that you most likely will not experience the motor jumping out of gear because of worn clutch dogs if the linkage adjustment is not properly set.  But also at the same time, it means that you should NOT TRY TO FORCE the shifting lever into a gear while the motor is NOT RUNNING because of these clutch dogs possibly not aligning when the motor is not running.  While it is running at a slow speed, these dogs are designed to engage easily. Otherwise, you could very well break the shift lever, especially the newer plastic levers, or bend some of the linkage if the older metal lever.  If you experience this and you HAVE to place the transmission in gear with the motor not running where the shift lever does not want to engage, (as if the transmission is stuck) try slowly pulling on the starter rope just enough, and at the same time putting pressure on the shifting lever, to allow the clutch dogs to mesh into the gear recesses as they do become aligned.  Using this method, you find the spot you will be able to move the shift lever from forward / neutral and then into reverse easily.

 

     Any time you may have a shifting problem, do not immediately question the gearbox, ESPECIALLY if you happen to be using a motor that is hooked up to remote controls.  The cables can become seized internally, or possibly stretched, out of adjustment or even become unhooked from the motor.  There are adjustments of the cables at the throttle/shift control ends.

 

    As a test, if you do have remote controls, disconnect them from the motor and try shifting the motor manually at the motor as a test as explained above.

 

   Experiences of a Owner & Verification :  "Hi,   There is a lot of good information here.  A couple of things that might be of interest to you.

   I had a 15hp Evinrude that was purchased new around Nov 85 and was designated as a 86 model.  It had the plastic top carby which cracked along where low speed adjustment goes within about two years.   The motor performed well at full throttle but you had to use the choke at low speed otherwise it would stall.   I fixed it with epoxy glue and used a sealer when I reassembled it as the back corner as did warp.   It was interesting to read your article about the extra screw modification.

   This model had AC lighting, cable throttle however the thermostat was located at the bottom of the head.  The stop button was at the end of the handle, but did not have the kill switch.

   This was a 100:1 engine and was almost always run at this ratio.  The engine was used on the back of a 11ft boat and was run at full throttle most of the time. The oil was a mineral generic brand.   I put around 300 hours on this engine before it was sold and the engine was still running strong.

   The main issue I had with the engine was cracked swivel brackets.  They would crack about 1cm behind where it contacts the trim pin. The first one was covered under warrantee, but I had to replace the others myself as they said it was a result of abuse.   They were $95 Australian each at the time and I fitted them myself.

   I also had a issue with one of clamps stripping, which was probably due to over-tightening and the fact the engine was removed from the boat each time after use.

   The biggest disappointment with this engine was it top speed. A number of my friends had the same boat with Japanese 15hp engines.  All of them were a lot faster with one or two people aboard, however when you put 3 or more people in the boat the Evinrude would be faster.  I spent a lot of time experimenting with engine heights, trim angles fuel mixtures and even had a custom propeller made as the biggest one sold at the time was a 9x10.   In the end I gave up and bought a 25hp Evinrude which had no problem outrunning the Japanese 30hp engines of the time.

    The link below will show you what type of boat it was used on if you are interested.   http://www.supaskua.com/

   Cheers, Craig of Australia"

 

   Checking & or Changing Lower Unit Oil :  Here are two flat headed screwdriver slotted stainless plug screws, one in the front bottom of the right hand side of the lower unit (gear case) with the other above it by 6 to 7”.  The lowest is the fill plug while the top one is an indicator of when the unit is full. 

   There is another round headed #2 Phillips headed screw above and forward the lowest flat headed slotted lower drain plug screw,  DO NOT TAKE THIS PHILLIPS SCREW OUT.   This Phillips screw is the pivot for the internal shifting mechanism in the lower gearcase.  If you take this screw out, then the whole lower unit MAY have to be disassembled to locate, reassemble the parts internally using a special assembly tool.  However first I would try draining all the gearcase oil, lay the motor on it's side, use a stiff wire or ice pick, flashlight, prayer, beer and are VERY LUCKY while having a steady handed friend slowly moving the shifter lever to realign it so you can locate the yoke pivot hole, get the screw back in place with the inner end going into the shift yoke pivot hole.   If this does not work, then remove the lower unit so it can be shaken a bit to maybe get that shift fork pivot hole in line with the gearcase hole.

 

   This shifting yoke was initially installed as the first thing during the final assembly of the gearcase.  If you can not get it aligned by the above methods, then total removal of the shafts, gears, and the bearings may be the final alternative.  AND YOU WILL HAVE LEARNED SOMETHING, AND NEVER REMOVE THE WRONG SCREW AGAIN.

 

    In the photo below this lower unit has been repainted so both of the screw heads are painted, otherwise they are normally the silver color of stainless steel.  This pivot screw is indicated by the red arrow.  The fill plug screw by a blue arrow.

 

    The simplest way to add or change this oil is to purchase from an OMC / Bomardier dealer, a quart of gear oil in a plastic pump bottle.  The pump spout has a clear plastic tube with a threaded end, that screws into the hole that you will remove the lower screw from.

 

   Remove this lower screw, check the color of the oil that comes out.  If the oil is, a golden brown it usually is OK, if it is blackish then it is probably OK, but really needs to be changed.  If it shows no water contamination, then quickly screw the pump tube into the same hole.  You will not be able to stop some oil from draining out while doing this, but if you act quickly, you will not loose a lot.  Then remove the top screw so  it acts as a vent.  Now screw the proper threaded hose fitting into the bottom hole and pump or squeeze the oil in until it starts to run out the top.  Replace the top plug.  In replacing this plug first, you are now creating just enough of a vacuum on the oil that will allow you to unscrew the oil hose, install this lower plug before a lot of oil runs out.

 

    The manual says it takes 9 oz to refill an empty unit.  If you are just topping it off, you may not be able to add much before it runs out the top hole.  If  you have drained the oil and are replacing it, you think you did not get this amount in before oil flowed out the top hole, you may be right.  What has probably happened is a air bubble formed in the upper cavity, which pushed some oil out above it.  Usually you can let it sit for a while and the air bubble will dissipate, allowing you to add more oil.  If this does not help, then run the motor a bit in a barrel on on muffs, then try again.

 

    While you have the screws out you should inspect the nylon seals, as IF they do not make a secure seal, water can get into the gear case here also and the price for these seals are about $.50 each.

 

    If it is a creamy to light chocolate color that means there is water in the lower unit's gear case.  If this is the situation, then allow all of the oil to drain out.  Flush it out with Mineral Spirits.  It is suggested that you simply change oil, replace the seal washers under the screw heads and run it, but check it every so often to see how bad the leak is.  If it slight and you are NOT using it in saltwater, you can get by for some time or until the next winter (slow season)  by just removing the lower plug screw, allowing any water that may have collected in the section to drain out and then adding new oil.  

 

    If it continues to leak, be prepared to at least replace the prop shaft seals and the drive shaft seals under the water pump.  There is also a O-Ring seal around the shifting lever rod into the gear case itself.  You should catch the drained oil, inspect it to see if there are any metal filings of any kind in it, which could mean damaged gears or bearings.  These seals are a double, back to back seals, you can not replace the outer ones only, since normal removal requires a internal type slide hammer which will ruin the inner seal.  Therefore to replace the seals, the whole gearcase will need to be removed and disassembled.

 

   There is an option when replacing this gear oil.  You can replace the oil with regular gear oil, called Hi Vis by OMC, or now you can get synthetic gear oil.  The synthetic oil does provide a slipperier, more efficient oil that allows the gear case to run at a lower temperature.  This is usually not a big issue with these smaller motors, as they are usually being only used as trolling motors and/or as an emergency “get home motor”.  The word is do not mix regular gear oil with the synthetic oil.  If you intend to use synthetic oil, drain the gear case and refill it with the new oil.  Then make a note somewhere that you have installed synthetic oil in the gear case.

   The Propeller :   OMC factory props are normally 3 blades which available in different diameters and pitches.  They fit all of the 9.9 and 15hp 2 cycle motors from 1974, along with the,  8,  9.9 and 15hp 4 stroke 1995 amd newer.  They all have the 13 spline shaft size and are designed for the thru the hub exhaust.   The most often seen being a 9 1/2" X 10" for both the 9.9 and the 15 hp.  This means it is 9 1/2" in diameter and rotates one revolution in 10".    A  9 1/4" X 8" is shown for the Sailmaster, with a power prop is listed at a 10" X 5".   The Johnson Sailmaster  or the Evinrude Yatchtwin have extra long (25") shafts and are designed to push heavier sailboats into and out of moorage.

 

   The 1991 OMC parts manual lists the following aluminum 3 blade props  --   9" X 10",  9"X 11",   9 1/4" X 8",  9 1/2" X 10",  10" X 5",  10" X 7", & a stainless in 9 3/8" x 9".

 

   However aftermarket prop companies such as Michigan Propeller make other sizes also.  This lower unit can handle a prop up to 10" dia.   A 10" X 7" or a 10" X 5" seems to be a good compromise for a heavier boat, OR if the motor is used mainly for trolling, as it will not lug the motor down as much and let you go a little slower.   These slower pitched props work best on a heavy sailboat as they give more control and give a better bite for reverse.  

 

   If the aluminum prop blades get dinged by hitting underwater objects, and they are not damaged too bad, you try to remove the dents out by laying the blade against some heavy metal object, then lightly hammering the bends out.  Then you should file the blades edges down enough to remove any roughness or deep gouges.   New replacement aluminum props run about $70 each.

 

   If you loose power but the motor continuers to run, the rubber hub inside the prop that connects the prop to the drive splines may have becomes un-bonded and is slipping.  You might be able to turn the prop by hand and see if it slips, or you can remove it from the motor and with a permanent marker draw a line straight across through the center.  Put it back on and the next time you have the lack of power problem, remove the prop and see if the lines still match or not.  If they don't it is a sure sign that the hub has spun.  These can be replaced at a cost of about $50.
 

   Removing the Prop :  The prop shaft splines should be greased with marine wheel bearing  grease when reinstalling the prop, to ensure that the prop can be easily removed next time.  These props have a rubber mounted hub, so if the splines are seized tightly enough, when removing a prop, the hub can be pulled off or pulled partly off leaving the prop blades misaligned and out of balance.  The nut, a 13/16" (same size wrench as the spark plugs) needs to be snugged down so that one of the slots align with the cotter pin hole in the shaft, but not so tight that it has to have an impact wrench to remove it next time.  However a air impact wrench may be the only way to remove a stuck prop since it has a rubber mounted hub and any other method may ruin the rubber.  Be sure that you replace the cotter pin when you replace the prop.  The factory recommendation is to not reuse the old cotter pin, since it could be cracked and if reused may break and come off possibly allowing the nut to work loose, thereby loosing the prop.

   Converging Ring on Prop :  On the original OMC and some aftermarket props, the rear outer of the prop’s exhaust hub is a plastic ring with a scooped portion pointing forward.  This serves a couple of purposes.  One is that since this motor uses an exhaust thru the prop, it then uses this ring as a scoop to force water into this center exhaust hole, forcing the exhaust away, not allowing it to build up a backpressure inside the motor at a lower speed.   This action of pulling the exhaust away will also tend to suck any of the unburned oil that accumulates inside the exhaust housing, especially if you use it mostly for trolling and do not run the motor at a higher speed for long enough time to suck the unburned oil out.   Without this function, oily residue can show up draining out the prop for weeks after it is taken out of the water. 

   The other thing it does is that when the motor is in reverse, it again helps relieve the possible exhaust pressure.

   Over time, these plastic rings can get brittle, then break off.  New ones are not expensive, about $10, and are replaced by simply laying the prop on a floor or workbench, then with a short section of 2x4, and a large hammer pound the ring onto the rear of the prop hub.  The prop has a slight groove that the ring snaps into to hold it in place.  You might consider doing this in a warm room so the ring has warmed up enough to not break it during you installation process.

   Remote Controls :  These motors were designed to be also used with remote controls.  But in purchasing these, you have to have three separate adapters and cable systems, (1)  the other for the  shifting lever unit (2) the other for the throttle system and (3) for the steering.

 

   First you will have to  acquire adapters to convert your tiller motor to be able to add the remote controls.   BUT, it is my observation that the post 86 to 92 motors seem to be lost in being able to connect a throttle cable.  If you go to http://www.marineengine.com/ , select you year and HP, on the bottom of the page is an accessory page link.  However it is woefully lacking factual data. 

   I suspect that the reason we see so little info on converting these to remote controls is that most of the motors rthat were fitted with remote controls  were sold by the dealers who then did these conversions after the sales and at that time they had better access to the factory kits.  And in these size of motors, probably less than 2% would be remotes.

 

 (1 & 2) There appears to have been 2 different OMC  "Remote Control Adapter Kits.   (1)   #386660 and (2)  # 398032.  These kits are only the adapters to the motor and did not include the cables or control lever box.  The throttle cable is ran thru the hole that normally is occupied by the kill button, then is attached to a peg located on the timing plate linkage rod.  On #398032, the kill button is moved over into the position under the RH front lower upper cowling where the starter button would have been.  The starter button is not be used in this case as if it was electric start, the starter switch would have been on the shift/throttle control box.   The #386660 kit is pictured below with it's illustrated installation sheet.  Here the kill button is moved to a new aluminum bracket that is bolted into the 2 existing holes on the front.
 
   The throttle cable was ran under the manual starter spool and attached to the peg on the vertical control shaft to the timing plate.  The twist grip handle was designed to be lifted into the up position, which  disengaged the cog teeth of the drive gears, allowing the cable to function without removing the twist grip unit.  This however creates problems when the motor is not operated with cables if the operator is unaware of the situation, as described later in this article. The angle that the tiller handle is mounted on the upper housing allows the handle to tip out and away from the motor for clearance.  If you snap the rubber cover off, raise the handle, you can see that the higher the handle is raised the farther disengaged the gears become as the throttle handle's twist shaft is not on the same plane as the intermediate shaft that the mating gear is on.

   The shifting cable was attached to the 2 plugged holes on the RH front side of the lower motor cowling.  And the cable end was attached to the upper hole in the shifter handle by a spring loaded twist pin.   The control cables must be type (OS) that means the plastic ends are molded on, not bolted.

 

   Also in the LH photo below you will see a quick disconnect clamp screw that attaches the older type pulley/cable steering system used before the more modern push/pull cable type became popular.  Here the center knurled knob us spring loaded and has  protruding pegs that insert in a double keyhole type slot for a quick disconnect of the motor without disrupting the cable.

 

    Shown below on the RH are the shifter split collar that goes in the location of the kill button with the push/pull cable inside it. 

 

 

   The throttle and shifting control box with matching cables need to have the proper length cables to go along side the gunwale and bend to the motor BUT they need to be long enough so as to not bind when the motor is turned n all directions.
 

 

   Factory outfitted remote motors usually have had a electric choke solenoid if they were in the mid 1980's or later.

    For the sail-boaters using these motors as auxiliary power where you may have to raise the tiller handle (which as noted before disengages the twist grip throttle) there may be a couple of alternatives.   The Sailmaster version of these motors designed for sail boaters is simply a extra long (25") shaft.  You could purchase a remote shift/throttle control then mount it near the helm.  Also extending the kill button wiring to the helm area would be beneficial.  You would not really need the steerage as you already have a rudder.  You may not need the full blown remote kit as your need for shifting gears is not great, yet at times essential.  

 

 (3)   If you were to use the more modern push/pull steering cable system and attach it to the motor, there is a bracket available that attaches to the transom and is the attachment for the outer end of the cable.  The end of the cable would then be attached to the  front end of this #386660 mount.  Now a Note Here, for these older motors do not try to purchase original OMC steering wheel, gearbox and cables, as aftermarket product has far outstripped factory ideas 40 years ago. 

 

    There are a couple of aftermarket companies who specialize in these items, Teleflex for one.  CLICK HERE  The one used most on smaller boats is a rack and pinion gearbox that the steering wheel attaches to and with a cable running rearward to the motor.  The cable needs to be ordered in specific lengths (taking into account for running along the side of the boat and back out to the center) being attached to the motor.

 

    One thing to think about if you are ordering all your stuff online, is that in all likelihood, you are not familiar with terminology or understand completely what you are ordering.  So do not be surprised if IF you order a steering cable kit, you may not even get the steering wheel.   My suggestion is to go to a local marine dealer and have them set you up.  Time and cost in the long run my be cheaper.

 

   Adjusting the Motor Pivot Tension :  If the motor does not stay where it is put when trolling, but vibrates and keeps moving from one side or the other, you may need to adjust the pivot shaft screw.  This is a screw that is mounted on the left hand side of the exhaust housing.  This screw has a coil spring under it’s head that you can not see.  By screwing this screw in, it tightens the tension on the motors pivot shaft.  Since it is located outside the midsection and if the motor is used in saltwater, this screw may become seized in the housing.  If this happens, avoid breaking it off in the housing at all costs.   I would, try to unscrew it, BUT BE CAREFUL that just the extended screw is what is turning.   A section in the trouble shooting repairs covers removing a seized bolt.   CLICK HERE

 

   Motor Mounting Clampscrew :   The 2 clampscrews that hold the motor to the transom WILL need service occasionally.  The pivoting handles of these screws should have oil placed on the pivot pins from time to time to keep them from seizing up and then breaking off.   To service these screws, it is best to remove them from the bracket.  There is a smaller screw that comes in from the rear and is screwed into the rear of the main clampscrew, holding on the large cupped washer in place.  Use a 7/16" socket wrench to remove this smaller screw, then you can unscrew the clampscrew and totally remove it from the front of the bracket, clean, grease, then replace.

 

    If the screw comes out hard enough to gall the threads in the bracket, you may need to run a 5/8 NC (National Course) tap in to clean up the threads.   However, by applying heat from a propane torch to the thread boss, then spraying the threads with penetrating oil has done wonders for me.

 

    Somewhere in production before 1983 the clampscrew handles were changed from aluminum to nylon.  The screw itself on the early models was made of aluminum.   You may want to keep these screws well oiled as replacement screw assemblies (the later screw is now stainless steel) cost $31.84 each, as of mid 2005.  In this area also later, about 1987 there were Zerk grease fittings installed in the front of the tilt hinge shaft boss, as shown in the photo above.

 

    Shown in the photo below are the motor clamp screw handles.  These are the later 1987 and newer.  The earlier ones were made of a aluminum, but I have seen 2 variations of them.  The overall length of all these handles were designed so that the ends have holes in them so that when the handles are rotated with both ends pointing inward a padlock can be inserted thru both handle ends.

 

 

 

   Reverse Thrust Kit :  I have heard about this, but never really knew what it was.  Many boaters thought it was heavier or different ratio reverse gears.  This seems impossible to achieve in the existing gearbox. 

 

   One day on my browsing e-Bay, I stumbled on the photo below.  Now if you go to one of the online marine parts sales (http://www.marineengine.com/) for example, find the year and HP, then on the bottom of the page click onto accessories, then to miscellaneous, you will find "Reverse Thrust Kit" listed.  Here it shows the parts in the e-Bay photo below.

    In this photo, you can see the shallow water/reverse locking lever and link being welded together (as evidenced by the black/brown metal discoloration).  I originally assumed for more rigidity.  But after thinking about it and only being used on the sailboat version motors, this version is so the more will not tilt up when in full power reverse which could be needed in a sailboat auxiliary motor.   The Ell shaped part is listed as a shift stop lock.  Not having the lock in my hands, I am not really sure of how it really functions.

 

    Also in what you can read on the instruction sheet in the photo, in the lower LH of the instructions, it says "Drill 4 holes each here" with a line pointing to the 6 holes in the rear of the lower unit housing.   I can understand that in sustained reverse, you may need more water coming into the water pump as the direction of travel has changed in relationship to these existing holes.   The thing I don't really understand is of the 6 holes there, 4 are already drilled through to the inside.  Maybe they mean to drill out the other 4 blind holes (2 on each side) for better suction to the water pump in reverse.

 

   One thing in this online list, it lists this kit for "longshaft" motors, which I guess that they assume these will be used on heavier/deeper hulled boats requiring more reverse thrust.

 

   On my 1992 9.9hp motor, it has these bars welded together.  So maybe the factory, over time, decided it was better to stock and install only the welded unit for them all.

 

 

 

   Has the Throttle Twist Grip Teeth Jumped a Tooth :  Check the twist grip to see that it has not jumped a tooth at the pivot point where the handle lifts up.  If this is the case, your throttle indicator for START will not be in the right location relationship to the carburetor and the timing plate cam.  This could cause the motor to not want to start when the throttle indicator is in the START position.  And if it does start it will not be able to run more than 1/2 throttle as the twist grip linkage will be off the one tooth.  

 

   AGAIN DO NOT RAISE the handle very high AND twist the throttle at the same time for the 74-86 OMCs while you are running the motor unless you are prepared to disengage the gears, and change the twist grip timing relationship.  This is explained in a subsequent section.  Later, in about 1986 a throttle cable push/pull system was used to eliminate this problem. in about 1986 a throttle cable push/pull system was used to eliminate this problem.

 

    You can check this by raising the handle, looking from the front at the mesh of the teeth on the 2 gears.    One has a WIDE tooth that has to mesh with the other gear that is missing a tooth.   If these teeth get out of mesh, about the easiest way to re-position them is to tip the handle as far rearward as possible, use a medium sized screwdriver, position the twist grip so it is aligned as best you can get it, then insert the screwdriver between the teeth, pry one tooth past the other and hope you do not break one off.  The other method is to pull the twist grip off, tip the lever rearward, slide the shaft forward, realign the teeth and reinstall the retainer screw in the twist grip.

 

    The nut seen here is the #83 nut mentioned in the #6 section above.

 

 

   Not Enough Tension on Tiller Handle :   For the early motors up to about 1986, if the tiller handle will not stay where you put it vertically, you will need to tighten it.  However this is not done as you would at first suspect.  The 3/8” nut showing at the hinge, when the handle is raised, is only a lock nut.   It has to be loosened, and the bolt's head end, that it is accessible from under the steering bracket needs to be tightened, then this visible lock nut retightened.  It is however recommended that you remove the bolt, clean the nylon bushing #83, then apply a slight amount of grease before you reassemble it.  If you do take this bolt out, be careful that you re-engage the throttle shaft dog teeth properly when you reinstall it.

   Cable Type Throttle Linkage :  Motors after about 1986 eliminated the gear disengage problem by going to a cable throttle linkage system instead.  The photo below shows a 1992 with the kill button on the side near the twist grip.  The earlier kill buttons were on the end of the twist knob, but the cable system was the same.

 

   If this twist handle seems to not want to move, the cable may be dry and binding inside, or the timing plate may also be dry and dragging.  To test this, remove the ball socket end of the cable at the timing plate, now see if the handle will now twist.  If not, then the problem is in the cable.  You may be able to remove the cable, then get some penetrating oil in to lubricate it.

 

   To disassemble this unit, you will notice a small round hole (about 3/16" dia. ) at the arrow.  There is another 180 degrees and on the bottom.  You need to use a couple of punches, depress both of these at the same time, while pulling the handle off front-wise.  A helper can be useful in this instance.  Inside this plastic is a dual rotating cam slot which a center cross-pin enters into spacers, and rollers (illustration # 3, 18 and 20 as seen below) which is in turn attached into the cable end.  When disassembling this handle, be careful to not loose these spacers and rollers.   With the center pin removed, this cable needs to be pulled outward through the handle.

 

   When twisting the handle, the cable moves in or out, activated by the cam slots that the rollers ride in.  This outer cable rear end is then secured by a pivoting ball in the lower cowling.  The rear inner cable has a screw on adjustable end attached to a small ball socket on the timing plate.  You can make some adjustment in this linkage by moving the threaded ball on the outer threaded cable, and or at the cable rear end.  If you are replacing the cable, be sure to set the ball and cable end at very close to what the original cable settings were, otherwise you may never get it set right, using a guessing game.

 

 

   There is a black plastic twist knob on the end of the twist handle.  This is a slow speed idle stop, (NOT A CARBURETOR IDLE ADJUSTMENT).

 

    This can be tricky to get set UNLESS the cable is adjusted properly on the low end of the speed setting.  And many times not worth the effort.

 

 
   One thing you may look for in the cable system, is that on the end of the cable where the nylon socket is that attaches to the ball, is this cable end seems to rotate slightly depending on the position of the handle's height.  The nylon socket is threaded onto the end of the cable's shaft.    The ball socket is not really designed for the ball to snap off the ball.   If someone has played with it and made that connection loose, it may pop off on it's own, time for  anew one at about $40.

 

   If this cable is not adjusted right you might have hard starting when putting the twist grip at the "START" location.  Incorporated in the end of these twist grip handles is a slow speed trolling type knob that can be rotated to supposedly a slow speed stop.  I have found that this slow speed knob many times does not work, unless you do adjust the cable end also.  To set the cable end, I would put the shifter lever in forward, then move the twist grip to where it will not go faster.  With the cowling off, you can see the neutral safety block of the shifter unit blocking the timing plate from further rotation.  I would use this stopped setting as a point to readjust the cable end so that the "START" position on the twist grip would now align with the pointer.  The rear end of the cable just snaps over a ball on the timing plate linkage.  Snap it down and off, twist it on the shaft, then try to see if things are better.   If it is so tight that it will not snap off the ball, you will have to unscrew the ball stud to make your adjustment.   You may have to do it a few times to see just where things line up.   Make an adjustment and the twist the grip to see what changes.

   You can now adjust the slow speed knob, (on the end of the twist grip) as your slow speed stop, after you have played with the idle knob, but in conjunction this slow speed knob. If you adjust one, you may have to readjust the other if at the SLOW end of the running.

 

    Occasionally you may encounter one of these cable systems that the twist grip will not stay where you put it.  The motor will usually slowly slow the speed down by itself, if you let go of the twist grip throttle.  A solution for this was passed on by a retired marine mechanic.  His solution was to take a electricians #6 copper grounding split bolt clamp, then simply clamp it around the throttle cable in an out of the way place.  There is enough room on the underside the the tiller handle IF you separate the plastic loom, AND slide the kill button wires to the side.  Tighten the nut enough to just squeeze the cable inside the plastic sheath.   Then tape up where you split the loom with black electricians tape.  Works like a charm.

 

    At this time OMC added the lanyard type kill button on the end of the twist throttle handle.  This created a problem if you used the extended universal joint tiller handle, as you could not reach the kill button with this extended handle installed.   A year or 2 later the handle was changed slightly and the kill button was moved to about mid handle left side.    This button is also a man overboard kill switch.  The motor comes with a red coiled plastic cord that is attached to a split plastic section that is inserted UNDER this button.  The other end of the cord is to be attached to the operators wrist, so that in the event he falls overboard, this insert is pulled out and the red button goes deeper in the housing, the connection is disconnected, just like turning a switch off.   In use this red button HAS to have either the lanyard insert under the button, (turning the ignition ON) or a another smaller that one called a restart clip that is inserted there if the owner decides he does not want the lanyard.

 

    On 01-01-2021 the USCG sent a memo out indicating they are now enforcing the wearing of this lanyard under numerous conditions, IF the motor was designed with this feature. "Operator Requirement:  An individual operating a covered recreational vessel shall use an engine cut-off switch link while operating on plane or above displacement speed."   For a link to that new law CLICK HERE.

 

   Zinc Anodes :  On motors from about 1983 on you may see (2) 1/4" holes drilled on one side of the cavitation plate.  These are for attachment of a zinc anode.  These anodes are threaded and bolts come up from the bottom with the anode on top of the cavitation plate.  These holes are evident in the picture below of the prop shaft being removed.    If you use your motor on saltwater, these anodes are a must. 

 

     I recently picked up a 1989 15hp that had seen LOTS of saltwater exposure.  It had the anode attached, which was a good thing.   This motor was to the point that another few years on saltwater and it would not have been worth much.  The parts above water must have been washed off with fresh water occasionally, but with the lower unit off to replace the water pump impeller, the whole insides of the midsection above the water pump had a GENEROUS dose of salt corrosion, enough that I doused it well with Salt Away before reassembling it.

    Removing Twisted Off bolts :  Here you MAY have some choices, depending on where it is broken, and if there is part of it protruding enough to get Vise-Grips onto etc.  The other option is to just leave it broken off and go with one less bolt IF that is all that is broken, if more than one then you will have to decide if it will create a functional problem.  Many times the stainless bolts are stuck worse than regular steel bolts, because of the oxidation between the two different metals.  And stainless is a lot harder to drill than mild steel bolts.  It will be a white powder.  I have not had any luck using an easy out in any of these instances.

 

 (1) If when you try to unscrew the bolt, it has resistance to where you feel it may twist off, (remember these will usually be 1/4" bolts) play it careful.  Usually if you try to use penetrating oil in this case the oil will not get UNDER the bolt head.  The corrosion will normally be between the bolt shaft and the metal surrounding it and not in the threaded area that it is threaded into.  My solution here is to use a small  angle head grinder, remove the bolt heads.  Now you should be able to pry the cover plate off these now bolt studs.

 

   Now use method #2 to remove what is still in the base material.

 

 (2) If you have broken it off, and it is protruding enough to get ahold of it, (1/4"), I would first soak the area with penetrating oil, If you do not have any, the best alternative is hydraulic brake fluid.  Build a dam around the broken bolt if possible with modeling clay.  Let it set for a few days, then during this time, tap the protruding end with a hammer a few times.  This vibration tends to break the bond and allows the oil to soak further in.  Now try a Vise-Grip pliers to see if it will turn.  If it does, only move it slightly, then back up, then try to loosen it again.  If you do it all at once, you can break it off again, and this time flush with the housing.  OK, this is the easy one if you got it out.  If not, then you might try to heat the aluminum up slightly with a torch in the area of the broken bolt.  Don't get it overly hot as you may melt the aluminum.  What this may do is about the same as tapping it with the hammer in that the aluminum will expand faster than the steel bolt, which may help break any bond between the two.  Do the soak and tap again.

 

 (3) If the above failed or the broken bolt is flush with the housing, I would again use the soak and tap/heat method, but now you have to drill it out as close to the exact center of the broken bolt as possible.  If it is a 1/4" bolt the hole size on the inside of the threads is about 3/16".  I would use a center punch, try to locate as near as possible the center of the bolt.  Remember that this small bolt the threads being a spiral, that you will see the outside of the threads, while on the other side you will be seeing the female part of the casting as looking straight down on it.  Try to locate the center where there are no threads.  Tap the center punch lightly.  Look to ascertain if it is near where you want it.  If not then place the center punch back in the original hole, then angle the head end away from where you want the hole to really be.  Tap it again at this angle and you may shift the original hole slightly.  When satisfied that is is as close as you can get it then clamp it in a large drill press or milling machine, so you can clamp the part rigidly so you can control the drilling.  If you do not clamp it securely to the drilling unit, the part WILL shift and you will drill off to the side.  DO NOT DRILL IT BY A HAND DRILL WITH NO RIGID SUPPORT.  Use a GOOD sharp drill bit with the hopes it will drill straight and not run out to the side.  You can drill it with a hand power drill motor, BUT the odds are that you will not be able to hold it straight and the bit will wonder.  Use a cutting oil on the drill as you are drilling.  If you succeed in having it centered, the bit will go hard, until it breaks out thru the end of the bolt inside the hole.  You may be able to feel the difference it at this point, as it will break into a hollow space below the broken bolt and into a deeper threaded section of the casting, as the threads will always be slightly deeper than the bolt. 

   If you did not get the drill lined up exact or it shifted so the drill took out just part (1/4) of the threads on one side, this should be no problem as there should be enough to still hold.  Now you can use an ice pick or cape chisel to get under one side of what is left of the threads & work them out, and possibly use a Dremel tool with a carbide dental burr to cut the bolt shell in enough pieces to extract them from the threaded hole.  This will free the hole enough to run a tap into it and clean up the threads.

 

 (4) If the above #3 failed and the drill ran out to one side, you will have to enlarge the hole enough to install a Helicoil.  This is simply a somewhat square wire tightly wound as a spring in the exact thread pitch as the desired new threads.  You will need to purchase a Helicoil kit, which includes  the proper drill size, oversize tap and an installation tool.  Here again it may be best to use a rigid drill press or milling machine, clamp the part to ensure you get it close enough to align the new threads to the other mating surface.  Here you might use a appropriate undersize end mill to clean up the butchered hole to remove what is left of the broken bolt before you use the Helicoil drill.   Follow the instructions on the tool.

 

   Converting a 9.9 to 15 HP :  This question seems to pop up quite frequently and can get controversial from those who have never been associated with the conversion and are only going from what they have heard.   As you can see from the above information in this article, it is possible.  New carburetors are expensive if even available, (well over $200), but used ones go for half that, then you can probably expect to rebuild it.  Some will tell you that you need different reed valves and reed valve stops.  I bought a 9.9 new in 1978 and still used it until I recently sold it.  It is the basis initially for writing this article, as I was trying to convert to 15 hp and there was no information, or reliable information available.  I also bought the repair and parts manuals at the same time.  From this parts manual I can assure you that the reed valves for either engine are the same for that year.   However in 1979 a .0125" shim was introduced that was placed between the leaf valve stop plate and the leaf valve itself for the 15hp motors only.

   I have not truly tested a before /after on the same boat, same water conditions.  But from information of those that have, the consensus is that it may not be worth the price or effort to change the exhaust tube when upgrading on the older motors, if trying to up the hp to the full blown 15hp, UNLESS you can find a used 15 hp tuned exhaust tube.  Remember that the older (pre 1981s) motors still used the same 9.9 exhaust housing on both motors.    I have compared the early 9.9 exhaust tube with the later and 15hp tube.  The mounting flange where it bolts to the powerhead is different, but it appears that the 15hp can be installed and would fit.   But just by changing the housing itself, you will not show many benefits.  Tuned exhausts are well known in racing two stroke motorcycles and are very effective at specific RPMs but need to be matched to the carburetor also.  

 

    Also if your boat is too large, heavy, or you and your fishing buddy plus gear are overloading the boat, your conversion benefits will not show.  However if you have a lighter boat and it just needs a nudge to get it onto a plane, then possibly going to the 15hp would help.  HOWEVER loading the boat (repositioning your fuel tank and battery) or re-proping, may be just as important, along with possibly adding trim fins to gain you that extra bit of jumping it up onto a plane.  Once it is on a plane, any extra speed will be minimal and only proportional to RPM increase.

    I will not go into exact part numbers for this conversion, as depending on your year of motor, a simple conversion could mean just a carb on say a 1977.  But if you wanted to wring every last bit out of it, you could also change the exhaust tube (3 types), reed valve stop shims and prop. Then if you had a 1990 9.9hp which is basically a detuned 15hp, just a carb may do it for you.

   In changing carbs, the older metal topped carb was used from 1974 until  early 1987 when the plastic topped carbs came into being.   If I was going to attempt this conversion, I would try to stay within the same range of carbs.  HOWEVER it would be entirely possible to use a older metal topped carb (more availability) on the later motors (87-92).

 

   The larger carburetor will gain the most in increased RPM, (about 1000 RPM more, according to OMC) which in this case also relates to more horsepower.  If you insist on squeezing that last ounce of energy, then maybe the aftermarket reed valves, polishing and deburring the intake manifold, replacing the exhaust housing will be of some benefit.  But, if you are trying to push it this far, at wide open throttle for an extended period of time, my thoughts are that then the rest of the engine may not stand up for long, so go to a larger motor.

 

    Props are listed the same for both the 9.9 and 15 hp motors, however depending on the weight of your boat, it may be advantageous to try a lesser pitch version.

 

   Also, as mentioned, the inner round exhaust tube was added after about 1981 for the 15 hp motors.  This exhaust tube on the 15hp has a circular cross-section and gets wider at the bottom, (like a long tapered funnel) called a TUNED EXHAUST as opposed to the narrow, rectangular shape on the 9.9.  This was probably copied somewhat off the tuned 2 stroke racing motorcycle exhausts of that era.   Part of the principle was that the burned gasses also carried noise waves from the motor, if these waves created a backpressure where the actual exhaust gasses put noise pressure at the intake ports at the programmed RPM to block fuel leakage at the same time having a more efficient exhaust so it could escape more easily.  When a motor breathes better, this equals more horsepower.  This is a rather complicated system using sound waves.

 

   Then in about 1987 another exhaust tube was brought out, this one is a short rounded unit and is used for both the 9.9 and the 15 hp motors.  My reasoning for the 87 date is that the 86 parts list still shows the old housings, where the 1990 list has the newer one.  However I have a 1989 that has the longer tube.  This motor underwent many changes in 1987 as to thermostat location, fuel pump, twist grip throttle, etc. where they actually produced a full15hp but they detuned it for the 9.9hp, as compared to the other way around up to then.

   On the later motors from late 1987 on thru the 1992 versions, when they changed carburetors, the inner exhaust tube is quite a bit shorter than the early ones and this same part is identical for both the 9.9 and the 15 hp versions.  Why, I am not sure at this point in time, unless it simply saves money on parts inventory and they found they gained enough by the other minor changes.

 

   So, In Summary of Converting to 15 HP :  If I have overloaded you with information on the differences between the 9.9 and 15hp, sorry.   I guess it is just how far you want to go in changing parts to do a partial or a total conversion.  Any changes will probably make a difference, (whether measurable or not) but to do the full blown conversion, ALL will need to be utilized.  However depending on the year of motor you have and your needs, a full blown total conversion may not be cost effective.  I have not listed part nomenclature and number for each change that they did over the 18 years of production of this series because of the various changes and some could have been superseded by other changes.  If you are that interested you will have to go back and re-read what I have posted here, maybe many times.  And then finding the correct part may be another issue.  I personally would have to really think a lot about doing it to say a 1974 motor, whereas if it was a 1988 +, that may be a more worthwhile project.

 

    A reader recently made the conversion on a 1976 9.9hp Johnson using the carburetor off a 1980 15hp Evinrude.  "The carburetor change upgrade results were fantastic.   21 mph GPS top speed with 9.9hp went to 27mph with the 15hp conversion on the same boat.  The reed valve shim and the 15hp exhaust will add a bit, but are not necessary to make a marked improvement to a old 15.    Do not get confused with people saying the intakes are different, or the head is different or the ignition is different.........THEY ARE NOT.   90% is all CARB".

 

   Another testimony taken from the i-Boats forum, "I had a 9.9 Johnson 2 stroke on a 16' Grumman V hull, it would start to get on plane but that's about it, it needed just a bit more power.  This was in a bare 4 bench seat hull with two 250 lb men aboard and a full 6 gallon tank.

   I eventually converted it to a 15hp by changing the carburetor and exhaust tube, that did the trick but it still only did about 18 mph".

   Converting Over to a Full Electric Start/Charge System :  This can be done, and is covered under it's own article.  To access it CLICK HERE

   Shaft Length Differences :   The standard motor comes to mount on a regular boat's 15" transom.  This is designed so that with the motor mounted on the transom, the bottom of the boat is even with the cavitation plate of the motor.  The cavitation plate is the flat fin in the lower unit housing above the prop.  The difference in the longshaft unit is that it has a 5” aluminum extension the same physical size as the exhaust housing, to fit a 20" transom.  This unit was supplied as a kit, comprising the extension, a new 5” longer driveshaft, a 5” longer shifting linkage rod, a copper water tube long enough to couple between the water pump and the old tube from the power head and 6 more bolts to assemble it to the gear case.  

 

   The SailMaster is basically the same 9.9 motor with electric start but with a 10" shaft extension for use on sailboats.  My 1981 sales literature says the SailMaster has a heavy duty reverse gears with a higher reverse thrust.  The parts list does not substantiate this however.  I suspect they simply used a lower pitch prop.   The Yachtwin, was Evinrude's version of the Johnson Sailmaster, same motor just a different color and name on the cowling.

 

   Short Shaft Converted to Long Shaft :  This is a common question, and to try to condense some of these repair articles I have moved this section onto it's own "Shaft length Conversions" section.

 

   Repaint :  You can purchase OMC Johnson original white paint #777171 specified for 1981-1990 at about $11.50 a can.   Tempo #0204601, (Johnson White 1981 to Present) which is an aftermarket marine paint for about $1.00 less, or Krylon brand which is available in about any hardware or automotive store, in about any color you want, it may not match exactly the original color however, but it is less than 1/2 the price.  I am torn between the Krylon brand and the original, as I like the idea of being able to touch up paint scratches if the need arises.  Krylon's Ivory Gloss #1504, is very close to the standard white that most of  many of these later motors were painted with.  I have found with the OMC paint, do not try to do thick coverage or it MAY wrinkle.  Do many thin coats. 

 

   The only drawback using a non-original paint is that it may not be as resistant to gasoline and gooey black oil as the factory or replacement types.  A cure for this is then a clear overcoat of Duplicolor 500 degree clear Ceramic Engine Paint from NAPA  be used.

 

   The 1974 Johnson OD green color was changed to white in 1977.  I have not found a good Evinrude metallic blue aftermarket paint.

 

    If you decide to repaint the cowling and the rubber motor seal is OK, you can pry it away from the fiberglass or plastic depending on the year, placing matchsticks between the rubber and the fiberglass to allow for a better paint job to go under the seal.  This original rubber seal is stapled onto the fiberglass.  If you need to replace the seal (about $40.00) after repainting, to reinstall it instead of trying to staple it, just use a latex adhesive and many old wooden spring type clothes pins until the adhesive dries.

    If you plan on replacing the decals, you will probably not be able to find any factory available earlier than about 1993 or 1994.  Price is about $40 for these original replacements.  If you purchase these later model decals, you will have to cut them to fit, as the newer side decals sets lower than you might think.  This is because the motors have a upper cowling that the seam is more horizontal instead of at an angle on the pre 93's.  This changes the position of the decals if used on an older cowling.  You will have to trim some off the front bottom at an angle of these side decals to get the lettering horizontally positioned.  And you will also have to trim the bottom rear decal to be somewhat close to a decent position.  Lay them out and tape them on the cowling before you install them.   You will not get a decal for the front where the control knobs are on these newer decals as there are none used on these later models.   UPDATE -- recently I found a company that appears to be able to supply about any motor decal, (even obsolete ones)  https://www.outboarddecals.com/ .

 

    There has recently became available on e-Bay, aftermarket vinyl decals that are generic for this series of motors at a price of about $14.00 to $38.50 a set.  These generic ones are quite good, a close coloration to the later originals, but do not match any specific year.  They have the "Sea Horse"  and appear to be die or laser cut.  They are made for both the Johnson and Evinrude  9.9 and the 15 hp.  The picture below appears to be on a repainted 1983, as it does have twist handle gears and the side idle control knob.  These aftermarket ones only have decals for the back and sides, not the choke indicator, shift positions, trolling speed indicator, etc.

 

    The later motors from about 1987 had the power head, flywheel and prop painted black.

 

 

   Commercial Motors :  I am making possible exceptions here.  Anyone who can clarify, please contact me.  Initially I thought all the gray painted lower sections were commercial motors, now I am not sure.  I can verify that at least a 1983 9.9hp and a 1984 6hp recreational motors were painted those colors.  So maybe somewhere along the line certain years and sizes of recreational Johnson motors were painted like this.   You can tell if the gray is original if the instruction decals are in white (as seen above) instead of black lettering.   This touchup paint is labeled "platinum gray" and listed for motors from 1984 to 1987.

 

   There is mention in the Sierra and NAPA catalogs of "Commercial" 10 and 14 hp motors.  According to the NAPA catalog, they were made from about 1988 to 1991.  It appears these are cheaper units.  They essentially are the same motor as the 9.9 or 15hp, but will have only a rope starter and with a tiller throttle handle system only.  They used the older CD ignition system instead of the UFI as used on the regular motors at that same time.  There was no provision for electric start or a charging system.   

 

   Some even use the older non thru the prop exhaust lower unit very similar to the older QD series.  And the NAPA marine parts book verifies this by listing gearcase O-Rings for these as the same as the 1957-1963.   My guess is that these were a sort of a "Clean Up" run made of older parts and sold thru some major discount stores, or for export out of the states.

 

   Non USA Made Motors :  Johnson and Evinrude made motors for worldwide usage, even having manufacturing or assembly plants in  Canada, Belgium, Australia, and Hong Kong.   Most of these motors DO NOT follow US model designations.  Many seem to be made like the motor was made later, kind of like a cleanup project into other parts of the world.  They can also be made using a newer powerhead mounted on a way earlier midsection/lower unit.    Most of these, the model number WILL NOT show on any US known model number lists.   For a link to a article covering this, CLICK HERE.

 

   Ongoing Improvements :   Other than the before mentioned changes, there have been ongoing improvements in this model since it's inception.  The throttle cable twist grip system incorporated in about 1986, initially still used the original kill button.  In 1987 the kill button was moved to the end of the twist grip control. There is a problem with this type, if some makes of extended tiller handles are used that the owner then can not reach the kill button when these handles are installed.  In 1991 the kill button was moved again to the middle of the steering arm near the rear of the twist grip, it utilizes the safety lanyard disconnect "Man Over Board" kill switch.  If this safety lanyard/clip is missing, or pulled out, the motor will not start.  If you are using the motor for a auxiliary motor, the safety type unit may just get in the way, so you can then purchase a override, which is a small red plastic horseshoe clip called  "clip-restart" #431808 for about $3.60 which makes a neat configuration which allows the motor to run, while still allowing the kill button to be activated.

 

    The SailMaster motors used a metal 3/16" rod that came out of the front cowling above the rope starter handle, went across and back in on the other side of the handle.  It was slightly arched upward in the middle.  Apparently this was to prevent the starter rope from becoming readily frayed if the motor was over the stern and lower on the transom than on regular boats.

 

    Each year had a different decal, so if you have a good memory, you could identify each year this way.  The earlier Evinrudes had a different motor cowling, in that it was slightly radiused on the front, back and had a slight hump in the middle.  The top cowling for the Johnsons appears to be change slightly in about 1987, in that the upper corners have a bevel of a little over an inch all the way around the top, they got away from the squarish shape of before.  This was needed for clearance of the newly repositioned thermostat from the bottom to the top of the head.

 

   HP Rating Changes :   Another point.   Up through approximately the 1985, the US engines were horsepower rated at the crankshaft.  Around 86, they had their horsepower rated at the propshaft.   This came about because of the imported outboards were outrunning the domestic motors of the same horsepower as the imports were rated differently.  This meant that around 86 and up had to make about 10% more real horsepower than the 85's due to the inherent horsepower loss in the lower unit gearbox.   My guess is that is why OMC made changes going to different carburetors at about mid year of 1986, trying to increase horsepower without major changes to the powerhead.  This gave them breathing room to do a complete engineering change for 1993 when they upped cubic inch displacement and horsepower along with a newly designed complete upper part of the motor.

   The piston diameter for both the 9.9 and 15 hp motors from 1974 to 1992 are 2.188" with a stroke length of 1.760" which equals 13.2 cubic inches or 216 cubic centimeters.  Full power operating RPM for the 9.9 is 4500 - 5500.  The 15 hp motor is rated at 5500 -7000 RPM according to a 1978 Johnson sales brochure.

   Sometimes referred to by marine mechanics as the "Big Block" 9.9s, the piston diameter for the post 1993s was increased to 2.365" requiring a different head gasket and the displacement was upped to 15.6 cubic inches or 255.64 cubic centimeters.  The .015" spacers under the reed valve stops designed for the 15 HP was then used for both motors in this era.   So now the basic motor has been redesigned to increase the HP for the 15hp unit without the add ons required to achieve it's rating, with the 9.9 now being the "detuned" carburetor version.

 

   Recommended Spare Parts :  If I lived in a location where spare parts may be harder to come by, OR you plan on keeping this motor, as parts for these motors are drying up.  I would consider stocking the following spare parts and in the following order.  Spare spark plugs would always be a requirement.  (1) fuel pump filter cap and gasket, (this cap made of plastic can crack).  (2) starter rope  (3) flywheel key  (4) small fuel hose clamps or Zip ties  (5) lower unit drain plug seals  (6) spare prop, nut and cotter pin  (7) water pump impeller  (8) fuel line primer bulb.  If for the older 1974 to 1976, then I would add points and condensers.

 

   Replacement Parts from Bombardier :  OMC sold out to the Canadian company Bombardier Corp.  in Feb.  2001.  Replacement parts for some of the older motors has dried up somewhat as the new owners may not be as committed to supplying older parts as under the previous ownership.   Now when ordering replacement parts, the dealer will see a new listing in place of  the older N L A .  This new listing is Vintage, which actually means No Longer Available.  Bombardier also changed the discount structure for many parts.  The retail prices are still listed, but the dealers get less of a discount and they now have to pay the shipping no matter what status they have.   Their website is very non-user friendly if you are trying to find parts.  The links do back to the preceding page, but if you do manage to get to a parts list page, there is no way to identify the hp,  just the year of the motor, so you have to guess.

 

   Replacement Parts from Internet Bombardier Supplier : There is one marine dealer that is set up to do internet sales and they have a very complete website that is user friendly with the availability to call up exploded views of the different parts for even motors 30 years old.   They have illustration numbers and corresponding actual OMC part numbers and prices.  Even list if any are no longer available.   Here is the link to their website  www.crowleymarine.com.

 

   Another one I have found that is fast and the price is VERY competitive is http://www.iboats.com/   They carry only aftermarket parts, like coils, rings, gaskets, powerpacks, carb and fuel pump kits etc.   They do not handle throttle linkage, clamp screws, decals or many of the individual needed parts.  They are cheaper than the NAPA or Sierra but use the same part numbers and you can specify which shipping you require.   The last electrical items I priced from a marine dealer for original parts was $160.  Sierra thru an automotive store was $120 with my friendly discount, plus freight, and iboats was $106 including freight.

 

   Replacement Aftermarket Parts : The Sierra catalog is available from Car Quest stores and  NAPA the catalog is available from them of course.  Many times you can get a part a lot faster by going thru these automotive stores, in that they are probably moving a lot more parts than a marine mechanic and your order can get called in almost daily.  But be advised that they will have to add on shipping, normally do UPS or FEDX air to keep their mechanics happy.  So, unless you specify that you do not need it ASAP, your shipping will be more expensive.

 

   One thing I have also found, is that these automotive parts dealers are just that, they usually are not knowledgeable at all in the outboard applications that you may require.  If you ordered off their catalog and ordered wrong, it is your responsibility to pay for it even if it is the wrong item.  I went this route once, ordered a thermostat kit #18-3674, thinking that I also needed other parts than just the thermostat that I might not have been aware of.  What I got was the thermostat along every gasket, spring, seal etc. that would allow me to fit it to MANY different models, for a price of $25.26.  I found out later that the thermostat alone #18-3672 (all that I really needed) would have been $11.86. 

 

   Also some of the NAPA gasket sets are not complete or they are misleading as to years covered.  They list the gasket set as fitting 1974-1992, WRONG.  For motors prior to 1977 if you order a gasket set, the water cover gasket, (the one the thermostat is under) gasket, is not supplied if you order the set, as there are 2 different water cover gaskets as described previously.  The older one from 1974 to about 1977, OMC #318917, is (NAPA #18-0397).  The later one from 1978 up to 1986, OMC #321387 which is they (NAPA) shows as #18-2905, and which they call "water cover gasket" is the one that comes in the overhaul gasket set, not both as you would think if there was an overlap.

  

   In reality I have found #18-0397  that they call "thermostat gasket" is the proper one, which OMC calls "water cover gasket".  Also If you order #18-0112 that NAPA calls the "powerhead mounting gasket",  I have not been able to find where it goes on this motor, but in reality I  really wanted #18-2907 that they call an "adapter housing gasket" that OMC calls "powerhead to exhaust housing gasket".   Maybe this  #18-0112 might just be one that fits some of the odd "parts" motors using a pre 74 exhaust housing and lower unit.  So buyer beware!!!

   One comment here on the electronic transistorized conversion kit.   I was at one time was quoted at about $60 for this unit.   Also from the experience of a marine dealer that says it does not work well if it is being used for trolling, as it appears the RPM is too low to give adequate ignition.

 

   Also be prepared to pay the shipping and handling costs, with an average about $6.00 for a $23.42 gasket set.  Where if you ordered it from a marine dealer and it was shipped with his other parts orders, he may well equal out the shipping costs.

Listed below are some of the normally used parts found in the respective Marine Catalogs for aftermarket Sierra parts.  It is found that they both use the same part numbers.  The bold numbers are current prices as of 7-2004.

                   

    Replacement Parts :  The one online marine dealer that seems to have factory parts for most models is http://www.boats.net/ .  Their website has a online illustrated parts listing.  Their parts are discounted off retail prices.  They even have a parts technician that you can call to verify if you encounter any questions.   I am not sure how old of models that they carry parts for, but I had no problem getting water pump parts for a 1977 Mercury 4.5 hp.  They then ship FedEx.   Another good source is http://www.marineengine.com .

 

   The Internet and e-Bay can also be a source of new or used parts.  However, if you are on e-Bay, then you had better be darned sure that you are bidding on the right part, as many of these sellers do not know the fine details as to interchangeability and they must think that just because it is a 9.9 that everything else must also fit.  Or they read somewhere that all the water-pumps are the same, so assume that everything else is.   I have tried on occasion to inform some, only to be told I was wrong and to keep my nose out of their business.   As you have more than likely concluded after reading this article that it is NOT ONE SIZE FITS ALL, especially in the electronics.  

 

    A few years ago, I bought engine parts off e-Bay that were advertised as fitting a  9.9, but the picture quality was poor, then after I received them, NOT  9.9 parts, so after much research and comparison, it appears they may have been for a 1989  6 hp instead.  The seller probably got them in a trade and had no real idea what they really fit.   Close only counts in horse shoes and hand grenades.

 

  I am still learning about some things pertaining to these motors even after 40 years+, so some information may change often.   And if I happen to answer a on-line question from a reader that I may have not thoroughly covered, many times I rewrite or add info & photos clarifying the issue.   I do wish to thank some of the e-Bay sellers from whom I borrowed some of the above motor pictures.   I have even been known to have to consult my own writings when I become bewildered (forgetful).

Copyright © 1998 - 2023 LeeRoy Wisner  All Rights Reserved

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Originally stated 06-1998, Last Updated   11-10-2023
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