Rebuilding a Trim/Tilt Motor on a Yamaha f90

Anyone who's owned a boat knows what a PITA it can be. If you have questions or solutions help fellow boat owners out!

Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby chris oak » September 3rd, 2016, 7:16 pm

This really is a referb diy but I put that so people can find it easier as I never found anything online.
The rebuild would be the same, you would need to buy the parts/brushes/etc.

Troubleshooting
On my trim tilt motor, I noticed about ten or so trips ago that the trim didn't work when I was running the outboard. I dismissed it because when I returned to port it was normal, this was a mistake because if I had fixed it right then I wouldn't have the problem later on.

If you push the trim on the throttle and it does not work, check the trim button on the motor. If this also does not work it can either be the solenoid or the motor itself. If one works in one location and does not in the other it is obviously the switch at that location. If you push the trim button and hear a "CLICK" inside the engine itself but no whirring of the motor the problem is probably the trim/tilt motor. If you hear a whirring but the motor does not raise/lower then you probably have a problem with leaking hydrolics although your motor can still be shot. You can check for 12v at the blue and green wires leading from the trim motor or you can disconnect the motor and try to jump it with a 12v source. If you take a small hammer and tap gently on the trim motor while pressing the button and the motor engages then your brushes may be shot or stuck/dirty. This is what was happening on mine and how I trouble shot it.

Here's something they don't tell you. On yamahas and other outboards there is a small screw that opens up a bypass for the hydraulics so you can manually raise or lower the motor.
On the yamaha f90 it is a screw that is on the bracket, you will have to look it up for your motor. If you take a screwdriver and unscrew it until it stops, you can lift the motor. What they don't tell you, is you have to displace that hydraulic fluid and that takes a lot of pressure, ie nothing moves when you first try to pull it up. The motor moves very very slowly, keep constant pressure and eventually you will slowly be able to raise it and then put motor brace lever up. On the f90, the engine is fairly heavy and I could do it alone but it sure would have helped with someone else. The engine also is so low that you will either have to have your boat out of the water or else you will have to be in waist deep or higher water while you try to lift it. Once you lift the motor and brace it, don't forget to tighten that relief screw.

On my boat the trim went out at the launch ramp when I was trying to raise the motor after getting the boat on the trailer. I knew of the release screw but didn't know how hard it was going to be to raise that motor, I also wasn't prepared to stand in deep water and thus I had to drag the boat up a few feet with the keel of the motor dragging on the ramp, this is terrible for the motor and you can break a lot of shit doing so. Once it was out of the water I could see the screw better and then after thinking about it for a long time, figured that you had to slowly lift it to displace the fluid.

Once I got home I started researching how to fix it, a new oem trim motor is about 800$ and an aftermarket is 200$.
If you are doing it at the dealership you are looking at about 1k including labor. My motor only has 500 hours, I was pretty certain it was the brushes but didn't think they would be that worn after 500 hours. I was looking to get it rebuilt, there's a guy in oc that rebuilds electric motors, starters etc and I was going to take it to him but he was closed on saturday.

The first thing you want to do if you do this is trace all the wires. If you cannot trace the wires then you are up the creek and you are going to have to either learn or take it to a dealer. I traced the wires, then turned off the battery and removed the two wires, one is blue and one is green. I took pictures of everything to make sure I could put it back together. Once you disconnect the harness you will have to undo different holders and work your way back to the motor.


To get the motor out, you have to use a pair of split ring pliers to take the washer off one of the lower spindles.
That piece of steel slides out and then you can pivot the motor assembly. Don't turn it too much or else you will chance breaking the seal on the piston side.

There are 4 screws holding the motor on, these are allen wrench heads so used my socket set with the allen wrench adaptors and also used a socket wrench universal joint to get the weird angles.
When you get that off and pull the motor out, there is a nylon bushing on the bottom of the shaft and that fell in the fluid canister below, so I used a turkey baster to remove the fluid and see how it works. Basically the shaft goes into the bushing which goes onto some sort of piston lever below. During reassembly you will have to line up the bushing perfectly so make sure everything is inline.

Once I had the motor off I was thinking that it can't be that hard to disassemble and if I screw it up I'll just take it to the motor guru next week or worst case buy another one. Either way if I didn't do it I would be looking at having my boat out of the water a few weeks and if I did fix it I could use it right away.

There are 3 phillips head screws on top holding the trim/tilt motor together, I took those off as well as the electric cord screws on the side. Then I carefully pulled it apart. The motor is well made and all of the parts stay together, as soon as the cap was off I could immediately see that the brushes were covered with dust and also one of them was jammed. I could also see there was plenty of life left in those brushes as they were hardly worn at all.


I used a paper towel and some probes and cleaned everything up and added a tiny bit of oil on the end of the shaft that sits against the cap. I used compressed air for computer parts to blow it out as well. The hardest part is pushing the springs and the brushes back in place, the brushes are cut almost exactly for their insets and I held them in with small probes (like dental picks) and then slid the shaft back in place and released the brushes/springs. Once that part was together I put the cap back on, it has strong magnets and you have to be careful to not break them with the motor windings. I screwed all the screws together and then turned the motor by hand to make sure it wasn't seizing. I then used a 12v battery to bump the motor and it spun easily.

Reassembly is the same as disassembly, the only exception is you have to line up that bushing EXACTLY with the piston unit below it, that is inside the cup housing where the now assembled motor shaft goes into. I put the white bushing back into the oil reservoir and then lined it up and then added the oil back in. I spun the spindle by hand until it was exactly in line with the female side of that bushing and slowly lowered the motor into place and luckily it all fit perfectly.

Carefully pull the wires back through all the spots they came from and use new zip ties on the outside of the motor. Connected it back to the fuse area, tightened it up and then turned the battery on. At first there was some air in the motor and I just heard it spinning but after a few seconds it immediately raised and lowered the motor.

This was a 2 hour job, but if I knew what I know now I could have done it in 30 minutes. If you do this just take your time, you shouldn't have to force the parts back together.

I used a variety of tools, like I said you will need an allen wrench adapter for your socket set or at least a set of allen wrenches, some antiseize for the screws when you are done and some dental picks. I used the compressed air for computer cleaning to blow off most of the dust. You really should buy new orings as well but I didn't this time around.
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chris oak
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby Bill McIntyre » September 3rd, 2016, 7:28 pm

If only I were as handy as you. After owning boats since 1968 and mostly paying someone else to do it, I might have money left to leave to my kids I had done the work myself.
email me at wsbhtr@cox.net
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby chris oak » September 3rd, 2016, 7:46 pm

Man Bill I appreciate the comment, it's not being handy, it's being frugal for me :). I always tell my younger buddies to take apart as much as they can, the same principals that run a motor in a grinder are the same as a starter motor or in this case the trim/tilt motor. I learn a lot at work because we have to take apart all kinds of pumps, filters etc. Keeping the motor running without spending all the extra cash means my wife is happier and I get to dive :). Thank god mine doesn't have expensive horses or else I'd still be in the kayak!!
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby Bill McIntyre » September 3rd, 2016, 8:25 pm

Let's not even talk about horses. :)

But you just reminded me of my excuse. I didn't get to practice taking apart things at work because they were too expensive. They let me fly jet fighters, but they had guys a lot smarter than me to take them apart and fix them. They asked me to just stay out of the way.
email me at wsbhtr@cox.net
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby greekdiver » September 4th, 2016, 6:00 pm

I did my 2006 90hp Suzuki as well. They were just orings to replace. My trim and tilt was much more difficult. I had to lift the engine off the boat! The new suzukis do not need that.

I feel like everything is easy to fix if you are willing to put in the time.
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby castronova » September 8th, 2016, 10:38 am

It's worth the work to save the money but it's also worth the learning experience so you can trouble shoot problems and not miss dive days.
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby Eric S. » September 10th, 2016, 9:56 am

I just got done rebuilding my hydraulic tilt/trim motor too.
Although mine was not an electrical problem. It's a 2000 Honda BF130.
A blown o-ring was my culprit. It was a pain in the ass to fix, but I have more time than money.
First I had to remove the motor from the transom. In the process, I did some damage to the gelcoat and fiberglass on my transom. Next was to remove the hydraulic motor from the engine mounting bracket. To do this, you must disassemble the transom bracket. In the process, I damaged my throttle cable. Next step was to remove the electric motor from the hydraulic motor. Surprisingly, I only managed to snap 4 of the bolts holding that part down (truth: there are only 4 bolts to snap).
After the disassembly, I needed to take apart the hydraulic motor. To do this I needed a special pin wrench. After receiving the overpriced pin wrench, things went smoothly. I had the motor apart, cleaned and reassembled in about 3-4 hours. It was a messy process, but not difficult. I found one blown o-ring, but replaced them all. About 16 total.
I have never done this type of work before, so I was pretty nervous when I went to test it.
Initially, the motor struggled to compress all three pistons and I had to kinda coax it along. But once all three pistons compressed fully and purged what little air was in the system, it worked like a champ!
The repairs to the transom and the replacement of my shift and throttle cables went smoothly and I am back in business.
I should have guessed, but after replacing the 16 year old throttle cable, it was clear the old cable was way over due to be replaced. The shifting and throttle are smooth as butter now.
Hopefully I can get another 16 years of use out of her now ;)

If anyone ends up in a similar situation, I have pin wrench you can borrow. It fits the upper hydraulic cylinder for Honda, Yamaha and Evinrude. You can buy cheap pin wrenches at most places, but they are designed for taking the blades off saws and stuff like that. The pins are too small for this application and will not hold up to the torque required to free up the cylinder cap.
Hopefully, none of you shall ever need it, but I will ship it to you if you promise to return it.
Will save you $90.00!
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Re: Rebuilding a Trim/Tilt Motor on a Yamaha f90

Postby Rising_Tide » September 14th, 2016, 9:54 pm

Thanks for another great DIY tutorial, I don't know how you find the time. My Mercury Optimax tilt motor hydraulic seals look like they need to be replaced soon... I'm planning on doing it this winter, not sure whether I'm going to tackle it myself, but you are inspiring me to try.
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