Outboard Motor Trim/Tilt Motor Replacement




There may come a time when you need to raise your outboard motor and it does not work.  The first thing to look for, would be a low battery or loose wiring connections.  This loose connections could be at the motor's up/down switches if it has them, or the remote switch on the remote throttle/shift unit, or wiring from the motor's relay box to the electric trim/tilt motor itself.


The unit we will be working on here is a 1980  70hp Johnson outboard which happens to be fitted with a jet lower unit.  And the need to raise it to remove weeds or gravel from the intake grates becomes a necessity at times.


This repair was accomplished without having to remove the oil reservoir on the starboard side.


This unit is a self contained hydraulic system.  In operation, there are small (5/8") twin shafts that are the primary trim pistons that are designed to raise the motor slightly to allow for the best angle of the motor for you to trim the boat for it's best planeing capabilities or to give you better handling ability in rough water.  After these twin pistons extend themselves beyond the normal trim height, the tilt piston which is centered between the electric motor and the oil reservoir takes over, which raises the motor to full height for traveling or checking or clearing any debris from the prop.


History :  This motor apparently was the last year that the Prestolite electric pump motor was used.   I had purchased the motor used and after about 3 years of use, this electric motor died.  I tired to purchase a new endplate with the brush assembly, only to find that this year of outboard used 2 different types of hydraulic motors so confusion existed in identifying needed parts.  Finally when the right endplate came in and installed, the motor still did not function.   So my friendly independent marine dealer offered me a complete used outboard motor mounting clamp / hydraulic pump assembly using a newer Bosch type electric motor off a 1984 120hp motor.  This was installed with no problems and functioned for another 6 years.


The apparent obvious difference in these two motors is that the older Prestolite motor used 3 wires while the later Bosch type used only 2 wires.  The motors would not interchange on the base assembly as the Prestolite was secured by 2 bolts to the base while the Bosch used 3.


Finally, during the preliminary "get ready for fishing season" work on the boat, it would not raise after a winters rest.  I traced the wiring, checked the connections and of course the fuse.  Once I got it going with the cowling off.  Replaced the cowling, then a no go.  Finally with the cowling off, I could hear the solenoids pop when the up or down buttons were pushed, but the motor would not run.


Hydraulic Pump Assembly Removal :  Next would be to remove the hydraulic motor/pump assembly.  First since the motor was down when the problem was discovered, the relief plug had to be backed off in order to manually raise the motor.   It needs a LARGE square shanked screwdriver and a 10" Cresent wrench for leverage.  This relief plug is so you can raise the motor if the pump motor is not operational.   All that is needed is to back this plug off a turn, just enough to allow you to manually raise the motor, (with the help of a friend).  Some oil will be forced out around this plug screw, so place a catch pan underneath. 


With the motor raised and locked in the up position by using the traveling lock bar, the hydraulic piston shaft cross pin was removed.


In this process of removal if the unit, it became painfully obvious that the 6 bolts that held this assembly into the motor's clamp mounting brackets would not readily loosen without twisting off.  There was a great possibility that this used assembly that I had purchased had came off a saltwater motor.


And the unit had to come off as one of the 3 motor bolts was inaccessible in the front.  Not much way to even get in to these bolts to use penetrating oil for any of the 6 bolts.  After a week of trying to come up with how to deal with this issue, I bit the bullet, then proceeded to twist off 4 of the 6 bolts.  Now the problem was that since these bolts did not break off flush with the inner housing but stuck out slightly into the side brackets, how was I going to slide this hydraulic assembly out the rear between the side brackets?


OK, so now the starboard side of the up/down pivot shaft's nut was removed and the 2 bolts thru the transom holding that side bracket onto the transom.  Now the hydraulic assembly could be pryed away, taken out after the blue and green power wires were cut near the motor.


Inspect What We Now Have :  First thing was to remove the electric motor, inspect it for possible repair.  During disassembly there was a lot of black sandy debris fall out, (not a good sign).  When it was apart, the brushes were worn down to where the commutator had worn 95% thru one of the braided copper brush wires as shown by the red arrow on the right below.  The blue arrow shows that brush worn just into the wire.


Not much hope of trying to rebuild this one and trying to rely on it later.  So a new motor was ordered.  One thing about mail orders is that the salesman in most cases does not know anything other than typing out an order.  For this motor to be properly assembled, the O-Ring seal needs to be installed between the motor and the base.  I was sold a package of O-Rings, that contained 5.  There also was one enclosed with the new motor.  Does anybody need 5 new O-Rings?


Apparently these new style 2 wire motors are common to many of the Johnson / Evinrude motors from 1981 on as there are numerous factory part numbers that refer to the latest number.  And the aftermarket new motors made in Taiwan sell for under $140 under Sierra's part number 18-6759.


Trim/tilt motor disassembled, internal debris & worn brushes Brush wire nearly severed


Twisted Off Bolts :  Shown in the left photo below are two of the four twisted off bolts.  The were soaked with penetrating oil, then pounded on with a hammer occasionally for a week.  Then even tried to be heated with a Oxy/Acetylene torch, however 2 of these bolts were so close to the reservoir that not much heat could be applied without fear of damaging the interior valves and other parts.  However one broken bolt was removed using a Vise Grip pliers during this operation.


With these 3/8" bolts that tight, it became obvious that ay Easy Out would not do any good, and would possibly even worsen things.  So on to plan "B".  This would be mount the unit on a vertical milling machine.  Since it was so large a unit, the 6" mill vise was dwarfed.  So a 10" angle plate had to be clamped onto the mill's table to hold the unit as square as possible.  Then some sort of clamping method had to be devised to hold the unit against the angle plate.


Once the unit was mounted securely, the tops of the extended bolts were milled off flush with the base so it would be easier to locate center because of the Vise Grips had chewed up what was protruding.  A sturdy center drill was used by eye-balling to locate and start the drill location.  Since these bolts are 3/8" and I wanted to drill out the body to as close to the inner thread size, a 5/16" drill was the right size.  These bolts are made of stainless steel which has a nasty habit of work hardening if the drill is dull, ran too fast and/or without lubricant/coolant, so the RPM of the mill was reduced to 240 for this operation.


A good sharp drill with lots of lubricant was used and everything went well in drilling out the broken bolt.  At the very end of the bolt when the drill caught, it pushed the short un-drilled end deep into the threaded hole, but this was OK as if needed, the new bolt could be and was shortened slightly to compensate.

In the photo on the right below one bolt has been drilled out while the other is still protruding.

Broken bolts during removal of the unit Drilling out the broken bolts in a milling machine


Clean Out Threads :  With the center of the 3 bolts drilled out, now an ice-pick was used to dig out some of the remaining threads.  A Dremel tool was also used with a small round stone to remove part of the old bolt that I had not gotten the drill exactly centered on.  Grinding and picking then now pieces and parts of the old bolt threads are shown in the photo below.


With the old thread pieces removed, a 3/8"x 16TPI tap was ran inside the threads to clean up any damaged areas.  Also this tap was ran thru the other good threads.  This drilled out hole may have become slightly enlarged since the center drill was not centered exactly, but enough of threads were retained to hole considering there were 6 total bolts holding this unit in place.

This particular unit uses (4) 3/8" x 1 1/2" and (2) 3/8" x 3" stainless steel bolts.


Before total reassembly a 3/8" drill was ran thru the clamp bracket endplates to remove any corrosion debris.  During reassembly of the unit into the brackets, a anti-seize compound was applied to both the threads and shank of the new bolts.


Broken bolts & the dug out threads after drilling


Reassembly :  In reassembly, there is a small size but large O-Ring that fits onto the bottom part of the electric motor.  Place this O-Ring on  the motor, not in the hole of the base.    If you do not have a manual depicting the recommended hydraulic oil, a good grade automotive automatic transmission oil may do.  Be sure any parts that go into the base below the motor are in their proper location.  Pour some of this oil into the base hole where the electric motor will set, (priming the pump).


Locate the wires coming from the motor, they will usually be positioned so they are on the outside of the unit, close to where they may go thru the transom bracket.  Clean the mounting area.  Most times you will have 3 mounting bolts for this electric pump motor.  Check the slot in the pump's exposed shaft, rotate the motor's shaft so it comes close to aligning with the pump's slot.  Position the motor on the base, you may have to rotate it slightly so the motor drive tongue goes into the pump's slot.  Once the motor drops down, replace the screws and be sure there are lock washers under the 3 screw heads.


Repaint It :  Original factory paint to match the year was obtained in a spray can.


Test It :  Now might be a good time to test it before final installation to see if this pump motor will rotate when you push the buttons.  If it does not, then check for loose wiring.

Tighten the relief plug screw.  In the photo below the red arrow points to the relief plug. 


The blue arrow is the oil reservoir refill hole.   If you have to remove this reservoir, the same O-Ring that seals the motor also seals this.  Fill it with the recommended oil.  Use a Plues oil pump can, pump oil in with the cylinder extended until it runs out the hole.  Replace the plug, run the motor thru a couple of cycles up and down.  Pull the fill plug, repeat the operation until all any trapped air is expelled.


The red arrow is the check valve bypass so that if you need to raise the main motor and the tilt motor is inoperative, you can back this screw out to allow the main motor to be raised.


In all probability, you will also have to add oil to the reservoir if the motor will not raise all the way up.  Or you mat have to "Bleed" it a few times to get any air out of the system.  If it will not raise enough, loosen the bypass screw and have a helper manually raise the motor, retighten the screw and try again.  This process may have to be done a few times and then re-check the oil level.


The fill plug seal is simply a 7/16" inside diameter by 1/16" O-Ring.


In the photo below you will see parts of the blue and green wires protruding from the top of the electric motor before they go out up and out thru the side bracket.


Replacement electric motor on left reinstalled ready to run again.



In trying to initially check the new motor, I plugged in the 2 wires into the motor's connector, grounded the body while pushing the up button, but did not get it to run.  My thoughts were that since it only had 2 wires the motor had to be grounded.  Apparently these 2 wire motors use one wire for power & the other wire for ground.   With the ground changing by going thru a solenoid box which switches the wires when the up button is pushed, then again when the down button is pushed.


This motor was the old white color, while later motors could be black.


Copyright 2010 -2015 LeeRoy Wisner  All Rights Reserved

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Originally Started 08-09-2010 Last updated 12-15 2014
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