Tuesday, February 21, 2012

Outboard Motor Trim Pump

This is the hydraulic trim and tilt unit for a 90 hp Honda outboard.  The unit did not work, so I checked the resistence on the electrical leads and found that it was an open circuit (infinate resistance).  The most likely cause of this is stuck or worn brushes in the motor.  In this photo the motor has been removed and is laying on the work bench, the red stuff is hydraulic fluid where the motor mounts.

When I took the motor apart there was a bit of rust and corossion inside.  The brushes appeared to be OK, but one of the springs had rusted away. 

This motor is built with an internal overheat protection.  It is hard to see with all the rust, but there is two round electrical contacts mounted on a bimetal spring.  If the motor overheats the spring will open the contacts and stop the motor. 

The contacts did not work anymore, so I soldered a jumper wire across them.  There will no longer be an over heat control on the motor, but I think that it is unlikely to be needed in our cold climate.  I reinstalled this part and replaced the spring in the brush holder and the motor runs great now.


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  2. Great post, thanks! I have a few questions do you mind helping me out?
    I am franticly trying to get the same unit working. do you have to remove the engine, take off the transom mounting plates to remove the trim unit? I took the top pin and bottom bolt out, the top moved freely but the bottom would not come out? also, was is difficult to take the motor off the unit once the 4 bolts were removed? I got all the bolts off (actually broke the head off of one...arrrgh) but could not get it to separate from the unit? I didn't want to force it. any help you can offer would be great... ryan (sitka)

  3. akwaves,
    To remove the trim unit from the motor you only need to take the top pin and bottom bolt out. It should just slide out, but it may be corroded. The motor should also come off once you take the four small bolts out. Give it a few wacks on the edge of the flange with a soft face hammer. Don't pound on the motor case itself or you could crack the magnets inside. Let me know what you find inside when you get it apart.

  4. I am back on this project. It managed to work off and on for the summer but finally died last week. So I have tried to just drop the unit out but apparently there are some bushings on the lower mounting bolt so I am trying to unbolt and loosen the left stern bracket so that I can separate the mouting brackets enough to pull the unit out. I will still let you know what I find when I find it! Do you think that the motor can be changed without pulling the while trim/tilt unit out? I have removed the bolts for the motor but I wonder if it can be properly bled if it is not level?
    Thanks again

  5. Hello

    Very nice post

    My name is Fernando Leitão and i´m from portugal.

    I need buy the brushes can you tell me where


    fernando leitão

    My email is: