Maintaining Johnson/Evinrude
4hp  R Model Outboards

1969 - 1978

 

  

 

 

One thing that I want to convey here is that I write only on motors that I have actually worked on, which overs a period of MANY years, consisting of many THOUSANDS of hours, and then more in maintaining/updating these articles.  They are motor specific, HOWEVER if you are having a diagnosis issue, my Trouble Shooting article covers MANY more aspects that may help you diagnose your issue.  CLICK HERE for access to that article.

 

   OMC (Johnson and Evinrude) utilized a lot of parts interchange between models and HP of closely associated motors in those days as it was simple to create "Families" of near HP size motors using the same parts, which was a great cost saving idea.  Here we will usually see many of the 4 hp parts be shared downward with the 3 hp motors, but not upwards with the 4.5 hp or larger models.

   General Observances :  The production of this series of 4 hp motors ran from 1969 to 2001, BUT there were MANY changes during this time.   These motors started with magneto system (points and condensers), then to electronic ignition being introduced in 1977.   The1978s and newer had a different fixed main-jet carburetor.  And then the later version starting in 1979 a totally different starter mounted in the new upper cowling and was used, and at that same time the remote fuel tank was abandoned, with a fuel tank in the upper cowling.  At this same time the carburetor was changed somewhat by adding a fuel shut off in the carb necessitated by the cowling mounted tank.   On this article we will cover a Johnson first and second years of production motors.

 

    Initially this motor seemed to grow from the previously made 3hp motor.  It appears that the factory wanted to cut costs from the 3hp and one would be fiberglass upper and lower motor cowlings, but to do so the standard (at that time) throttle/magneto advance required the front of the cowlings to be open so the timing plate lever protruded in front.   For this motor they did a whole new lever on the LH side, rather unorthodox, but it gave them time to develop the newer twist grip throttle system.    Matter of fact the last year of production for the 3hp was 1968, but it (in my mind at least) was actually the prototype for this 1969 4hp.

 

   The odd part is that on this version, they reverted back to the adjustable main-jet that the pre 63 3hp motors used.

 

   The most noticeable part of this motor is that what you would normally think the right side lever would be a shifting lever (WRONG) it is a throttle lever.  The earlier 5hp had this throttle lever on the left side.  This motor DOES NOT have a shiftable gearbox, so it is in gear all the time.  Reverse is obtained by rotating the motor 180 degrees.  This cuts down on weight and cost of manufacturing.  It was designed as a fishing motor, (trolling) for small boats, and it did an admirable job at that for a decent price.  It was made to use a remote fuel tank, which was rather new at that time for a motor of that size.  It was made with a standard lower unit, OR a Weedless version (same as the older 3hp).  The difference was the standard propeller shaft was at 90 degrees to the motor driveshaft housing, while the weedless prop shaft sat at a downward angle.  And very seldom seen was the folding driveshaft version.

 

Here is the 1970 Evinrude Lightwin version

 

   It is my opinion that they were designed to compete directly with the Eska and Clinton motors being sold by Sears that at that time were using basically 2 cycle air cooled lawnmower motors.  These air cooled outboard motors did not idle down anywhere close to what the water cooled name brand motors did, but being CHEAPER, they cut in to the name brand sales.  Some first time fisherman did not really know what they needed, and purchased through a catalog or non fisherperson sale staff, but over time, may have found the error of their ways.

 

   This 4 hp motor does not follow the normal line of progression as far as to yearly manufacturing, therefore it is my guess that they (initially at least) reverted back and cleaned up the warehouse using discontinued/obsolete parts and simplified it (or tried to) as much as possible.  By this, it appears the starter was from the earlier 3hp and the carburetor also reverted back to the dual adjustable idle AND high speed knobs.  But the fuel pump was the same small square one as used on the other motors made at this same time. 

 

   All three of the main bearings are simply bronze bushings cast into the aluminum block, and the connecting rod bearings are again simpler by just being reamed in the aluminum connecting rod.  This requiring a richer fuel/oil mix than other OMC motors made at the same time frame.

 

  Statistics For These Motors :

 

These motors develop 4 hp @ 4500 RPM

Cylinders                      2
Bore diameter          1.560"
Stroke                       1.380"
Displacement           5.28 CI
Bearings,   bronze bushings, both mains and rods
Johnson Tillotson type carburetor with choke, throat dia. .612" - Carb kit Sierra 18-7043
High speed jet, adjustable up until 1963,  Starting point 1/2 turn out
Idle jet - 1 1/4 turns out as a starting point
Fuel cap.  Remote with fuel pump
Fuel mix is Oil 1/3 pt. (22 :1) SAE-40 per Gal
Point gap is .020"
Plug gap .035", Champion J4J or J6C spark plug.
Flywheel key - Woodruff .154" (5/32") wide x .235" thick x .603" long
Flywheel nut  - 7/16" NF, -- 11/16" wrench size
Water Cooled - rubber vaned impeller type - Sierra #18-3001
Gearbox oil - 90 W gear oil
Gear Ratio -  14-25

Prop. dia. & pitch- 3 Blade, RH, 8" x 5 1/2" 

Shear Pin -  1/8" X 1.00" OAL, along with a rubber shock absorber hub in prop 

Prop nut retainer pin  -        3/32" X 1 1/4" cotter pin
Prop nut, brass slotted-       1/2" NF , with rubber nose cap

Weight 29# for the RW & 33# for the RH

 

    Free Motor :  The motor being covered here was initially a gift to my neighbor from his daughter-in-law after his son had passed away.  This motor had bee sitting for "A Number of Years" and was totally seized up internally.   He needed one for his 10' Columbia fiberglass boat, so maybe this would fill the bill.  He asked me to give him some guidance.  Well, first we pull the head.  WE only twisted off 3 of the 6 head bolts in this process.   With the head off, WOW, both cylinders were rusted badly and the pistons stuck/rusted into the cylinders.  He used penetrating oil for over a week and every time he walked by it in his shop, he would rap the top of the highest piston with a hammer on a large wooden dowel, but with no movement at all.  OK, he asked me what next.  Well, we need to remove the block off the exhaust housing and tear it apart to access the connecting rod bolts so the pistons could be driven out the top.

 

Here is what we saw when the head was pulled,
pretty much indicative of salt corrosion over a long period of time

 

   First off, we/he needed to remove as much rust from the cylinder walls as possible so that they could be driven out the top.  Clean up as much as possible with a wire brush, then inside the cylinders, using a pocket knife and then 60 grit emery cloth, try to remove as much rust as he could, and more penetrating oil.

 

   With the block split apart, which allowed us to remove the connecting rods, then again using the large wooden dowel, pound on the top of the pistons a bit and then alternating onto the connecting rods that had the caps replaced.  So back and forth numerous times and finally one moved, and we were then able to remove it, then came the other.  Those cylinders were rusted, and from the appearance from a LONG time after being ran in saltwater, then possibly the motor may have been tipped up where water inside the exhaust housing had ran back into the cylinders through the exhaust ports. 

 

   The rings were intact on the pistons, but he broke 2 of the 4 in taking them off.

 

   But until we got to honing them, we were not sure that we could salvage this little gem.   They were rusted badly, but not deep and for the amount of usage he would give it, with a LOT OF HONING, in all probability the motor could be salvaged.   Some parts, including gaskets and bearings were not available, but he had already purchased new rings and head gasket for close to $70.   I showed him how to make some of the cover plate and manifold gaskets, by using bulk gasket material covering the part, and a small ball peen hammer tapping around the edges of the metal part.

 

   Here You Are :  Since he had no idea of what all was needed in this rebuild, and I was his coach, UNTIL he apparently had a chance to really sleep on this project and evaluate the situation.  I then became the new owner of lots of parts, (as seen in the photo below) like I needed another hole in my head.   About the only reason (my sane mind?) that I even accepted it, is that I had already started this article, so why not continue and finish it.  No sense to tear apart a perfectly good motor just to get information and dimensions for writing an article.

 

    First off, here I needed to see if I could get the powerhead repaired enough to justify any other work.  The more I dug, it looked like there MAY be a possibility that I could salvage it.  LOTS of work, but possible.

 

   Well, it only took a couple of years before I got around to tackle this project, thankfully all the parts were still in their boxes.

 

Here you see the motor, (all in pieces) that I will be covering here

 

   There being numerous replacement parts unavailable, or if so, at an exurbanite price, and/or existing ones worn considerably, this project can probably be considered a Red-Neck repair, and is not very high on my priority list.

  

   The one good thing that everything under the flywheel (points, condenser and coils) looked brand new.

 

   The cylinders were honed until MOST of the pitting was removed, going out to almost .010" oversize.

 

  The head was warped enough that it had to be sanded down flatter by laying a sheet of 80 grit sandpaper on a flat surface and doing a figure eight with the head on this sandpaper while pressing down on the head.

 

Here is the head after resurfacing it, not perfect, BUT?   Before cleaning

 

    Piston Rings :  These rings are rather delicate being only .061" wide X .055 thick with a bore diameter of 1.567".      (1.580" honed out bore)

 

        Installing Pistons :  When installing the pistons, they need to be positioned properly for the engine to run right.  These pistons, (like most 2 cycle) are designed so that incoming fuel does not flow over the top of the piston and out the exhaust port.   To make this happen the pistons are designed with a abrupt upward lip on the intake side.

 

     In the photo below you see an illustration of the orientation of the piston, with the sloped side toward the exhaust.  Here the top of the piston, on the intake side (spark plug) is designed so the fuel is directed IN and UP, more like being trapped on that side at the end of the intake stroke instead of allowing it to be blown across the top of the piston and loosing some of the fuel mix out the exhaust.

Here you see the piston orientation

 

 

     One thing on these motors, if you remove the head, it may be a good idea to mark the TOP.   However the spark plug holes are offset to one side (to the RIGHT).  On this model the spark plug locations are designed to match the contour of the tops of the pistons.  The head needs to match the top protrusions of the pistons allowing for the combustion (spark plug side) like in the photo above which would be the RH side here.  This head can be installed upside down and will run, but will not run efficiently, as it can not utilize the fuel from the intake ports as designed.  And the top corners of the piston ridge may hit the head. 

 

     The top (upper area) of the head has a slight 1/8" X 3/8" protrusion slightly positioned to the left.  The head gasket also has a mating protrusion, this is an indicator which needs to be in the UP position.

 

Here you see the spark plugs REALLY offset to the right

 

    Powerhead Bearings :  The center and lower crankshaft bearings are cast in bronze bushings (no rollers) and the connecting rod bearings are simply a bored and reamed hole in the aluminum connecting rod, very similar to the Briggs & Stratton lawnmower bearings.  The top main bearing is a caged needle roller bearing with 27 needles. 

 

   With this bronze type rod bearing, being mandatory that this motor use a richer fuel/oil mix (24-1) than currently recommended for the modern needle/roller bearings.

Exploded view of the 4 hp powerhead unit.

 

   Lower Crankshaft Seal :  One thing that seemed odd when I into into this project, is that there was no lower crankshaft seal at the block, nor attached to the upper driveshaft like the 5, 6 and 8hp models.  Below the lower crankshaft bearing, in the block, is a groove below it for what seemed like may have been designed to accept a seal, but upon investigating, this recess was apparently just for a upward protruding ring on the upper part of the clamp bracket/ exhaust housing that was for block alignment. There is a shallow circular groove in this alignment bushing that could possibly accept a 5/8" ID dia. O-Ring.

 

   OR, maybe with this motor requiring a richer fuel mixture, that in itself, being more oil settled at the lower part of the crankcase, and may have been enough in this small a motor to seal it.  ??

 

   Now here is something else, in the lower main bearing journal of the crankshaft is a small woodruff keyway.   At each mating bronze bearing, on the sides of this bearing is a small cut at the exact distance down as the keyway.  It seems that maybe this could be a method of distributing any accumulated oil throughout the bearing.

 

   Thermostat :  These motors DO NOT use a thermostat, probably, (1) to cut costs and (2) since it is a small enough motor, they possibly then designed it so the size of the water passages through the head gasket are enough to balance between it being warm enough for full combustion of the fuel AND yet enough flow to keep from overheating.

 

Here you see the rebuilt block

 

  

   Magneto Ignition, Points & Condensers :   If the ignition is magneto type, using points and condensers, the points were universal from the 1.5 hp up to 30 hp from 1952 to 1976 and then even to some 40 hp motors to 1973.  Condensers pretty much followed this pattern from the 1.5 hp to the 35 hp at 1976 (excluding the 9.9/15 which are different).

 

   On these motors, all the points are set at .020".   If you get a motor that is not firing, pull the flywheel then clean up the points with a point file.   The last point file I purchased (2009) cost $7.50 from a auto parts dealer.  Sometimes all you are doing is to just remove oxidation off the contacts if the motor has sat for some time.   This can be usually remedied by running a point file thru the point openings to freshen up the contact metal.  Most of the service manuals say to replace the points if worn or burned.  Well, take it from me you can usually clean them up for many more hours of run time afterwards.

   However if the points are really pitted, that is a sign that the condenser is not performing to capacity.  If this is the case, then it is recommended to replace them, along with the condenser.  The one thing that does wear is the points rub bar if it has not been lubricated from the last repair.   

 

    If you replace the points and still have running problems, you may well could have contaminated the point surfaces with oily fingers.   If this may be the case, remove the flywheel, rotate the crankshaft until one of the points are open, wash it off with lacquer thinner, rotate and do the other set.  Then insert a section of brown paper shopping bag in the points, rotate the crankshaft until the points close then pull this paper thru the points.  This should clean them.

 

   This older ignition using condensers, if they start to break down, the motor can start and run for a while, but when things warm up, the condensers, and or coils can begin to short out internally which may cause the motor to die.  You can crank until you are blue in the face but it refuses to start.  Let it set for an hour, which allows these components to cool down and it MAY then restart.  Time to change condensers, however hang onto the old ones as long as possible as the newer manufactured ones have a reputation of not being made that old high quality.

   A condenser is simply a lot of aluminum foil wrapped between waxed paper as an insulator.  If the paper starts to deteriorate, after running for a while, the metal will heat up then expand.  IF this happens in a location where the insulation is bad the metal shorts out to the next wrap, nullifying or shorting out so no output is achieved.  But IF this is the case, many times when the condenser cools down, the short goes away until it warms up again.  Once it has done this process a few times, then the short becomes rather permanent and the condenser can become inoperative

   If that driver coil (under the flywheel) starts to fail, is cracked, or starting to melt down, or whatever, there is a possibility that it would also operate when cold, but fail by shorting out when heated up by the running of the motor.   However do not just replace them because they are oozing black tar like goo.  They may still run for some time.

 

   For a more in depth article on magneto ignition along with fine tuning the point settings  CLICK HERE.  This article is directed mainly at the 1974-1976  9.9/15hp OMCs, but the principal is the same for about all of the magneto ignition OMCs even with those that have external coils.

 

   Coils :   Coils for these points and condenser motors are the same from 1949 mostly up thru 1973 from motors 5.5 hp thru 40 hp.  This motor's coils are mounted on the timing  plate under the flywheel.  These coils, especially those in the 1960's motors have a reputation for cracking and allowing moisture in and then starting to break down, creating problems.  The factory (or supplier) changed the plastic formulation on the coils at some stage and the replacement ones are considerably better.    If the coils have cracks that you can see, they maybe also have cracks below which could be allowing electricity to short out to the plate.  If you are on a tight budget, remove the coils, dry them out, then paint the cracks with a thick paint or epoxy, which MAY get you by.

   About 60% of the older motors I have had, needed one or more coils replaced, and the current replacement costs range from $20 to $25 each, which would be financially unviable for someone not working on their own old motor with the price of labor at $95 an hour to not replace them.  But the mechanic is covering his behind, because of you possibly later having one/them fail and he would get the motor back for free repair only to find that in his saving you money he actually got an unhappy customer and him a repair where he felt he had to cover at least part of the second repair.

 

   After doing some web surfing I found a website by Doug Penn where he showed on a video how to test both the coil and condenser of older OMC outboards.  CLICK HERE for a coil testing video, and  HERE for a condenser testing video.

 

Top view of the really clean magneto/timing plate with both
the points, condensers & coils

  

  Recommended Spark Plugs :  The recommended spark plugs for these 4 and 5hp motors were Champion J4J, however if you are using it for a lot of trolling, I go to the hotter J6Js, which is a hotter yet and used mostly in lawn mowers, trimmers etc. , but my thought is with these older motors, where the coils are getting old and these motors need all the spark they can get, especially at a low speed.   The R designation is a resistor type which would be beneficial if you are running a depth finder (helps cut out electrical interference).  The recommended spark plug gap is set at .030", however with a well used motor where the rings may be worn and may oil foul the spark plugs, old some mechanics may recommend try to open the plug gap up from the normal to .035" or even .045" which seems to allow the plug to run hotter and burn cleaner.  However maybe a better solution would be to a move to a hotter plug, like the RJ6C, especially when doing a lot of trolling.

 

    One notable thing on this motor as compared to it's previous 3 hp cousins models is that the spark plugs are mounted in the head at a dramatic angle to the right.

 

   Fuel Pump :  This motor was designed to use a remote fuel tank, which was rather new at that time for a motor of that size.  This requires a fuel pump.   These tanks are usually 3 gallons as compared to the regular 6 gallon ones as the consumption for these motors is less along with 3 gallons are less weight than the larger tanks.  The pump used on these motors was common on all OMC outboards form about 1965 through the late 1990s for about all their motors no matter the HP.

    This fuel pump seemed to function, (using the mouth blow/suck method on each fitting) but it needed attention, in replacing the center filter/ inlet cover with a new stainless steel one in a larger size, along with replacing the badly corroded attachment bolts.  There was already a new inlet fuel line, which was the only new part on the motor.

 

     The fuel line quick disconnect coupler is the same single line used on all the later motors.

 

Here you can see the  RH side of the powerhead with the fuel pump

 

   Carburetor :  This carburetor needed a complete disassemble and clean/soak in carb cleaner.

 

   To remove the carburetor, you will need to disconnect the fuel line, the choke lever and both the low and high speed knobs.  These knobs just pull off the finely splined shaft straight forward.

 

   You have to You have to remove the starter to access the LH carburetor mounting nut and remove that nut.  

 Here, you will have to remove the starter handle, holding onto the rope to keep it from unwinding, pull the rope in through the hole in the cowling.  Tie a knot in it or replace the handle, now you have the rope free from the motor other than and being contained in the starter unit itself.   Now remove the rear top bolt (using a 5/16" wrench) from the recoil starter spool mounting plate that is one of the inspection side plate cover screws. 

    Then using a 5/8" socket wrench, unscrew the main starter spool retainer bolt.   Very carefully pull the complete starter to one side just so far that do not pull allow the recoil spring to escape out of the base.   Add a 5/16" NC nut to the starter spool shaft to keep the spool and the spring from coming a nightmare.    Now you can remove the RH carburetor nut, slide the carburetor forward off mounting studs. 

 

   The normal initial setting for the idle (slow speed jet) would be 1 1/2 turns out from lightly bottomed out for either style carburetor.  Where the normal starting point of the high speed jet would have been probably 3/4 of a turn out. 

  

   This carburetor is fairly simple design, (a slightly different version of the popular 3hp model) being held on by (2) 1/4" NF nuts.   The throttle lever is unique here and not on the front like most, but on the RH side of the cowling.   This carb has an exit throat diameter of .735".  FYI, the manifold inlet diameter hole is oval .500" high by .725" OAL.  

 

    There is no breather as was on the earlier 3hp brother models.   It is the basic simple standard unit and possibly one of the last to use the adjustable main-jet style.   There is no carburetor cam roller, but simply the carb arm (#26) rubs on the timing plate cam.

   Number 15 in the illustration below is the idle adjustment needle, while #23 is the high speed adjustment needle.  Number 9 being the choke lever.

 

 

Early,  adjustable main-jet Carburetor

 

     The main jet is mounted in the bottom fuel bowl part of the carburetor (also known as the high speed jet), and is adjustable (protruded as a twistable shaft).  The upper knob is the low speed or idle adjustment.  These knobs are adjustable on the shaft so that once you find the desired setting, you can reset the knobs to a desired number, (usually #1) if it, (the knob) is round, or have the pointer aligned, usually UP.   This is accomplished by the shaft being internally threaded to 6-32, lightly serrated, AND split.   The knobs have a bore that fits closely onto this split shaft.  A tapered head screw being screwed in after the knob is installed, where this tapered head screw expands the split shaft, tightening the knob in place.  If you loose that screw, a easy replacement is one designed as a retainer for electrical outlet covers.  

 

 

   Throttle Control :   The throttle control lever is located on the right side of the motor and raises about 6" up on the outside of the cowling.  This is many times confused with a shifting lever, however these motors pivot 360 degrees  for reverse.  The Fast, Start, Slow indicators are a decal on the lower cowling behind the lever.

 

   It has a rubber friction tube inside the lower cowling supporting this lever shaft and tension adjusted simply by squeezing the cover for the rubber, using it's 2 mounting screws.   Inside the cowling and next to the block his inner part of the throttle arm is then attached to the timing plate by a arm and wire rod, which in turn moves the throttle cam to the carburetor.  The speed indicator decals are placed on the top part of the lower cowling behind the lever/arm.  There is no Kill button, as with the lever all the way back is enough to change the timing to where it will die, if not then choke it.

 

Here you can see the throttle lever  & the speed indication decals on the RIGHT side of the motor's lower cowling, (NO TWIST GRIP THROTTLE)

 

 

   Recoil Starter :    This recoil starter uses a unique rotating/pivoting vertical gear that when the rope was pulled, the gear unit pivots up engaging the flywheel ring gear teeth which are on the under side, engaging the flywheel ring gear teeth which are on the under side, not outside of the flywheel.  This version was initially used on the earlier 4hp motors and later used on these 4.5hp motors.
 
    This starter assembly that is ALMOST impossible to assemble off the motor (like most others can be), it can be done HOWEVER IF you have the right equipment.

 

Side view of the 4hp starter unit.

 

     One unique thing on the 4.5hp is that if the twist grip throttle handle is advanced to FAST, the ratchet disengages and will not allow the motor to be started.

     In working on this one, try NOT TO let the rewind spring get out of the cage.   It is not anywhere near what you may have encountered before, and you will have an experience.  

 

    It can be removed from the powerhead without taking the powerhead off the midsection/lower cowling as it just has enough room to get a wrench on this starter pivot bolt head.   With that said, there is a trick to install this unit back on.   In initially removing it from the powerhead, it may be best to BEFORE you start, to get yourself a 5/16" NC nut, so you can captivate this unit, by installing the nut on the rear of the center bolt as you remove the unit to keep the spring from unraveling.  Upon reinstallation, be very careful to squeeze and maintain pressure as you start the center bolt and do it's final tightening.   

 

    In all probability, if you have to replace the rope the rewind spring will not stay contained, here is a description of how to rewind the spring. If you have an original OMC service manual the last chapter tells you how to install the spring. here let us assume you don't have that one. Read this a few times before starting, as I'm probably leaving out some of the obvious stuff.

    Before you start clean all parts in paint thinner and then give everything a good coat of new light grease. And be sure the 3 Nylon bushings are in place for the shaft to pivot in.
At the back of the spring cup there is a slit where the spring enters into the cup and retains the spring's end loop when assembled. If you had to let the recoil spring unwind in order to get the outer tail end in the proper slot in the spring housing, wind a few wraps in the housing, locate this exit slot in the housing and get the spring going out (there will be LOTS of uncaptivated spring outside) the housing now.

   This starter pull cord goes on clockwise. FYI, someone said the length is 68", NO -- about all I can get on the spool is 55". With the recoil spring removed, wrap (RH) the pull cord all the way on it's pulley and then take an elastic band, or masking tape, and place it on so the pull cord stays in the pulley.

    In the initial assembly, the spool and outer cover needs to have the small gear located between the 2 ears/stop tabs of the rear spring cup.

   You will see a hole in the casting looking at you where the pivot for the small gear is. Fit a snug fitting drill bit in the hole. This is designed to use the force the drill bit up so the small gear stays meshed in the flywheel teeth. You now need to cut a wooden wedge that will go between the top of the lower pan and up tight against this drill bit, forcing the small gear into the flywheel ring gear teeth. It has to be tight, otherwise the gears will un-mesh on the final spring tightening.

    Once you get everything aligned and the unit bolted to the powerhead, take a socket wrench on the flywheel nut and start turning the flywheel clockwise (with spark plugs removed).

    As you turn the flywheel the spring will commence winding into the cup. Once the entire spring is in the cup go one and a half turns more. Keep pressure on the drill bit (as mentioned above) to ensure gears stay meshed and the spring stays wound on and in place. You can remove the rubber band or masking tape. Take the loose end of the rope out from the spool, feeding it off the bottom and feed it out of the cowl, pull enough extra and tie a slip knot on the outside of the cowl. Put the handle on the rope's end and release your knot, and the rope should wind back into the recoil. If you need it tighter, it is possible to wind the rope one, or more times onto the spool, however it may be easier to remove the flywheel to accomplish this, as you can now feed the rope through onto the spool to tighten the spring and retract the starter pull handle.


    One thing that I have found, the aftermarket 1/8" dia. starter rope is slightly tight in the spool and may not want to allow the rope to fully recoil at first. Here you may have to judiciously use some course steel wool to remove the newness.

      TIP --- Wear old clothes as I always end up filthy during recoil work. And it my be best to have a few anti-depression pills handy.

 

Exploded view of the 4 hp starter unit.

 

 

   Upper Motor Cowling :   This cowling is a slightly miniaturized version (shortened by about 1") from the 5 and 6hp models made during closely related times.  However the latch was a combination of others models, but closer to the 6hp of the same time period.

   Motor Mounts / Swivel Steering :   There are no real motor mounts (as used on larger motors) on this small motor as the rotating pivot shaft takes up all the thrust and with this small a motor there is not a lot of thrust on the mounting clamps.  Here, the rubber steering column mounts act as the anti-vibration motor mounts.

 

   OK, now it is together, but the 360 degree steering is very hard to rotate the motor.  I am this far, nothing else to do but tear that apart also.  

 

    Here for easier access, by tipping the motor upside down, there are 2 bolts top and 2 more on the bottom holding the front half to the rear half of this swivel bearing unit  Once apart, you will notice a top and a bottom rubber ring that has some 1/8" vertical holes in them.  Inside these rings and around the column are thin plastic friction bearings.   What I found was the aluminum column had very bad corrosion, which was sanded down and a bit of WD-40 sprayed on.

 

   Reassembly proved impossible until I noticed that these rubber rings were not round on the outside, but had opposing flats matching the housing halves.   Also inside the front upper rubber ring recess is a floating clamp bar that by tightening a large bolt head (located front underneath bracket assembly), put tension on this bar, creating steering friction.

 

   Tilt Lock :   This motor has no actual tilt lock, but just a fiction fit on the tilt hinge bolt.  It does have a 4 position trim lock however.

 

   Water Pump :   The water pump housing was made of pot metal and had a bit of wear, but not enough to hurt, as I by using sandpaper and a block of wood backing, sanded this roughness out, trying to match the inside contour.

 

    This motor uses the pot metal water pump housing, however it looks pretty darned good along with a impeller that does not have a lot of set in the vanes.  HOWEVER, apparently the 2 screws holding the pump body to the gear case, must have at one time been seized, broke off and butchered trying to "FIX" the issue.  The rear hole was intact, but the front.   Someone had tried to drill the broken screw out, and broke a drill bit in the hole.   They then still dried to drill that out, only to drill out through the RJ side of the screw boss on the gearbox. 

 

   The lower unit's water intake had a homegrown heavy duty stainless steel screen pop riveted around the outside of the housing.  I should have taken a photo of this, but never thought about it.  Upon inspection, there was supposed to be an internal screen wedged inside of these outer intake slots in the lower unit.  However there was enough extra to fashion a new screen and place it inside like the original.

 

   To remove the lower unit/gearbox, there are 4 bolts at the lower part of the exhaust housing that attach the gearbox to this housing.  Remove them.  The gearbox and driveshaft should now slide down and off the water pump outlet tube that is attached to the bottom side of the powerhead.   Do not try to carry this unit by only lifting on the exposed driveshaft as it will pull out of the gearbox.  You can then remove the two screws holding the upper water pump housing, which allows this housing to be slid up the driveshaft, exposing the impeller.

 

   This water pump does not use a upper shaft seal, but relies on a wider band of rubber on the impeller to seal around the shaft against the pump's housing on top and wear plate on the bottom.

 

   The water outlet tube from the water pump up to the block is 1/4" copper tubing and uses a  threaded fitting into the bottom of the lower pan that is in turn bolted to the block.

 

Here the water tube from the water pump and the exhaust tube attached to the lower pan

 

   Water Intake :  These motor's main water supply to the water pump comes from water intakes are on each side of the rear of the gearcase housing, (not shown in the photo above) and in front of the prop.  There is an internal inner screen #15 (now obsolete), behind the intake holes.  This screen was made in a Vee shape and held in place by being wedged into the cavity from above and the top of the gearbox and under the water pump).  These in takes are seen above the vent plug screw in the gearbox photo below.

 

   The early motors used a pot metal water pump housing (now obsolete) and the impellers used on this motor up until 1975  were OEM impeller #0277181,  or if aftermarket, Sierra #18-3001.   If the motor (or if the water pump was replaced) uses the later plastic pump assembly OEM #0379770 (introduced in (1975) then use impeller OEM #0763735 instead.   The impeller key is made similar to a Tee, but the single protrusion is round going into a hole in the driveshaft, where the to of the Tee is square, fitting into the impeller keyway.  This impeller has six vanes and dimensions are approximately .50" thick, 2.74" diameter, shaft hole ID .440"

 

   Water Pump Re-Assembly :   I have found it best to inset the impeller into the housing with the vanes rotated as if the motor was being rotated clockwise looking from the top.  I usually lubricate the vanes with a slight amount of oil or Vaseline.   Place the impeller in/on the water pump housing, being sure you install the impeller in the same rotation that the motor will be turning, RIGHT HAND looking down.  Rotate the impeller as you force it into the housing.   Move the impeller so that it's hole in the hub is pretty much in line with the housing shaft hole.  All vanes need to point the same direction.  Install the impeller key #13 in the driveshaft.  As mentioned above this model's key are made in the from of a Tee.  The bottom peg is rounded that goes into a hole in the driveshaft, leaving the top of the tee which is rectangular slide into the square notch in the impeller.  These are not available anymore, so a substitute would be an 1/8" x 5/16" minus stainless steel rod.   Here the hole in the driveshaft is blind (only going in part way) so the length is critical.  By saying 5/16" minus, I want to leave enough extra to be able to fit the length very close to just fitting the impeller slot.

 

   Slide the water pump housing (with the impeller down in place) onto the driveshaft, moving it enough to get the impeller and housing to both accept the driveshaft.   Be sure the impeller key in the shaft retainer hole has the hex part of the key vertical to be able to accept it's mating slot in the impeller hub.   Slide the housing farther down onto the key.   It wants to turn sideways slightly enough during assembly that you need to have it rotated very close as the 2 slide together to assure it is right.  The water tube outlet will be to the rear.  Bolt the housing down to the lower unit base using anti-seize on the threads.

 

Here the water pump impeller is shown

 

    One thing when reassembling anything on the lower unit that MAY get exposed to water (especially salt water) is to coat all the bolt/screw threads with a anti-seize compound.  A later mechanic will thank you.  As this motor all four of the lower unit fastening bolts to the exhaust housing were corroded enough that they all twisted off, requiring more tedious work to remove.  As viewed by CLICKING HERE.

 

   The above also applies to the upper driveshaft spline, grease it with a good grade of waterproof boat trailer axle grease.  This will ensure that the next repairman will be able to remove this lower unit/gearbox when he needs to replace a water pump impeller.

 

   Gearbox :   There is no gear shifting, so just a simple set of bevel gears are in a modular cast gearbox with a removable rear prop-shaft bearing plate.  This 4hp appears to use the same BASIC gearbox as the previous 3hp or the short production run of the 5hp.

 

    To remove this lower unit (gearbox) from the exhaust housing, remove the four 1/4" size (3/8" head size) bolts from the bottom side of this unit where it bolts to the exhaust housing.  WARNING, in all probability these bolts will be seized and if you unknowingly think they are starting to unscrew, THEY WILL BREAK OFF.  Looking at the lower part of the exhaust housing above where these bolts are located, you may see some slight holes.  This will be the location of the bolts.  It may be best to soak these recesses with a good grade of penetrating oil for a week or so, hoping to elevate the chance of any bolt breaking.   If not then you will be in for the task to remove these broken bolts, while saving any threads in the housing, (Not An Easy Chore).

 

    Seen in the photo below are two silver colored dime size threaded in plugs, with the words Oil Level above the upper one.   The other "Fill" plug is on the lower edge of the radiused gearbox.  You remove the upper one, then remove the lower, quickly insert the gear oil fill nozzle and squeeze oil in until it runs out the top hole, which is the proper amount.

 

Side view of the lower "R" unit/gearbox showing the water pump setting on top and the water intake slots 

 

    Now again looking at the photo above, line up the part you can see of the driveshaft above the water pump, and visually extend it into the gearbox.  It comes out nearer the front than the rear, and to make it as simple as possible, the driven gear on the prop-shaft is rearward of the drive gear on the driveshaft.  This would, in normal shifting type gearboxes be the reverse gear that is being driven, which is not used here.  Therefore these props have Left Hand blades and turn backwards from the normal ones.

 

    To get into the gearbox, remove the (2) 1/4' slotted bolt heads (#22) from the rear bearing housing #20 in the photo below.  This housing does not have a flanged gasket, but the housing slides inside the gearbox about 1/2".  In the middle of this mated housing, in the middle of this housing, is a Neoprene O-Ring as a seal.  So if after you get the screws out, this housing will not lift off, but needs to be rotated to where a screwdriver tip can be inserted under the screw bosses to pry the housing off. 

 

   Propeller :  The prop, as mentioned above the props are LH rotation.   This motor uses a 3 blade aluminum prop in  8" X 5 1/2" size and has a 1/2" prop shaft hole.  I can not find a part number on it, only the size.   The hub diameter is larger than normal for this size a prop because of the rubber clutch.   These props had the drive/shear pin forward of the rubber drive hub, with a threaded hex nut on the outside rear.   The shear pin is stainless steel 1/8" (.125") diameter X 1.00" Overall Length.  These pins appear to pretty substantial and I doubt if they would break before a blade on the prop would.

 

     This prop nut is a 7/16" X 20 NC thread and has a circular groove in the center of the hex where the cotter pin can be pinched over and into.   This appears to be the same as used on the early 5hp motors.  Forward side of the nut's hex is a 1/8" turned down section for the rubber cap/nose cone to snap over the complete nut and cotter pin to retain it.  This rubber nose cone has to be pried off rearward and if it has not been off for some time the rubber may become slightly torn.

 

   They made a slight improvement over the 5hp prop, in that this 4hp, which incorporated a "clutch" #28 (OEM #0310331) in the illustrated photo below.  It is simply a rubber double cog ring (cogs on the inside AND on the outside).  As seen below, it fits snuggly inside the prop, and the prop clutch hub goes inside of it, creating a connection.  But over time, this rubber can deteriorate, allowing the prop to slip at a higher RPM. 

   This particular motor's clutch was corrodes/seized so badly that I just left it alone.

 

    Also the outer prop shaft seal (#21) was improved and still available  OEM #0313730.  The shaft diameter is 7/16".    

 

Side view of the lower unit/gearbox showing the water pump setting on top and the
water intake slots 

 

 

  

   The gearbox oil was still good and with no apparent leaks at any seals.

 

   The gearbox had numerous holes drilled to attach a Red-Neck water pump strainer screen.  I filled these with Bondo.  It also hosted both water pump housing bolts that had been seized AND tried to drill out, with the front hole drilled out of the threaded boss, exposing part of a broken screw.  OH yes, that gearbox if tipped sideways or upside down during these repairs allowed the gear oil to run out of the driveshaft hole.   This was solved temporarily by purchasing a tapered cork plug with the top diameter of 9/16".

   By me using my trusty Dremel tool and small carbide cutters, I was able to, by going into this now hole in the outside of the gearbox grind enough of the aluminum away, allowing the broken drill bit section to be removed.  And more grinding, got the old screw out.  Quite a hole now, but by using Vaseline smeared on a new 10-24 screw, I mixed up some JB Weld, installed the top of the water pump, (held in place by the rear screw) put the new screw in the front pump housing hole) AND added my JB Weld, tamping it in around the screw.  In doing this I added enough JB Weld to also build up the screw boss, that was no longer there when I got done removing the broken drill and what was left of the seized screw. 

 

Here is where the stuck drill bit was in the gearbox that was in the front water pump screw location

 

   Then came cleaning the lower pan, and attaching the exhaust tube and water inlet tube to the   .

 

   I then used the old heavy duty stainless steel screen that had been wrapped around the gearcase housing over the water intake.  Here, by cutting this screen longer than needed, by trial and error found it to where it would just slide inside the cavity (like the original). 

 

   I used 2 new #10-24 stainless steel crews to attach the water pump housing to the lower unit.  Installed the pump.  Then installed the water pump, (with new impeller) and a red-neck key onto the drive shaft, bolted everything in place, and slid the units up inside the exhaust housing to engage the driveshaft splines into the crankcase.     .

 

    Below you can see the finished product, lots of head scratching and very few parts misplaced in all the moving of the torn down motor along with probably over a 3 year span.  Considering the condition that this one was, it is one that really should have been used for a boat anchor.

 

Here you can see the finished product

 

    The Rest of the Story :   With it all back together, compression on #1 was 70#, but #2 was only 30#.   Did I break a ring when I reassembled it?  OK tear it down again.   What I found was the rings were OK, but after a lot of honing that cylinder to clean up the cylinder bore rust, it was slightly over .012" oversize.   And it also appears that the ring grooves may have been wore to where the rings were wobbling.   So with the combined combination that was there, not much compression.  

 

     What to do now???  New pistons were unavailable, and probably would not help much if they were.   This project was not worth putting a lot of money into.  OK, my plan is to order new wider rings (these are .061" wide), where it's early 3 hp predecessors that used used the same piston, but with wider rings (.091").  I can order custom rings from OTTO GAS ENGINE WORKS, at a real reasonable price.  If I get wider rings and to fit the oversize bore, then lathe turn the piston to match these wider rings, that may solve one issue.  Then I took the piston to my welder friend who aluminum welded a ring around the top and bottom of the piston, which I then lathe turned down to match the cylinder bore.  Now I have the piston fitting snuggly top and bottom, and better heavier rings that fit the grooves.   Sure there is a gap in the center of the piston, but the proof will be DOES IT RUN ?

 

Here you can see the piston after the welding & before the lathe work
 

 

 

     This was rather an unorthodox repair, BUT what the hell, I could not ruin it anymore than it was, and it may just raise the compression enough to get it running. 

 

    This was a project from HELL and nothing that I would recommend to any sane minded person.

 

     Project number 2, which was a 1971.   Here I bought it along with an old gas tank with hoses from a relative of mine.  I asked for a history if known.  His response was it came with a boat that he had bought and was running then, but was missing the complete choke rod/knob.   He also said the starter also appeared to be slightly hanging up so he liberally applied penetrating oil and that it cleared up.

 

    Well the first thing I did was try to pull the starter rope, NOPE - NO WORKY.  Thinking it was still in the starter as he had mentioned, I pulled the cowling off and again tried the rope, NOPE.  The flywheel was seized.  Also the high speed carburetor was bound up tight.   I did not ask him how long ago he bought it nor where he had it stored in the intervening years?   I did not want this one to slide, so that afternoon, I contracted and asked, he said he unseized it a year ago????  But he sure as hell did not offer that information when he offered it to me.  Another experience in buying/trading old motors and horses NEVER ASSUME ANYTHING.  Looks like I had just bought a old gas tank.

 

   OK, I pulled the plugs, soaked it overnight with a mixture of light oil and SeaFoam, then I broke it loose with a socket on the flywheel nut and a 16" braker bar.  I then hooked the socket to my 1/2" drill motor and spun it enough to loosen things up.   Compression is 98# on #1 and 60# on #2.   Not ideal, but if I can get it running and flood it with rich mix of SeaFoam, hopefully the bottom cylinder compression may raise.

 

 

 

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Originated   01-02-2018, Last updated 04-30-2023
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