C90 Trim Unit Question

[MarshMarlowe]

1997 Yamaha C90TLRV

I just picked up a 1997 Key West 1720 powered by a 3 cylinder Yamaha



I park the boat in my driveway. My driveway has a funny angle that prevents me from lowering the motor all the way down, so I leave it trimmed out a bit. I noticed today that the skeg was almost on the concrete, and that's definitely not the position where I left the motor trimmed, so it seems that the engine has slowly come down from the position I left it in.

I inspected the PTT unit closely, and don't see any signs of a leak. I tightened the manual release screw, but of course I turned it to the right first since righty is usually tighty, but turning it clockwise releases the trim, so I'm not sure if it was actually loose. I'm going to monitor it for a few days and see if the motor falls again.

Anyone had this happen before? Could there be air in the system? Or a leak I'm not seeing? A seal failing internally? Thanks!

[rodbolt17]

while all don't do it, its not uncommon to see them leak down over 24+ hrs.
as long as it holds when your running and no fluid is leaking.
run it.
BTW, that's what the trim support lock is for.

[robert graham]

My 1999 C90 tilt will leak down very slowly/overnight...I've never worried much about it since there's no obvious/visible fluid leaks....if I want it to stay up I use the tilt lock lever....I guess there's some kind of internal fluid leak but I'm not much worried about it.....While trailering I use a transom saver bar to keep motor up in place....

[MarshMarlowe]

Thanks Rodbolt and Robert. That's one less thing to worry over. I'm aware of the purpose of the trim support lock. I keep a fitted cover on the boat, and raising the motor that high creates a pocket in the canvas that will hold water.

[rodbolt17]

that does happen.
NEVER trailer it on that lock.
not saying you don't have an issue.
not saying you do.

as long as you don't have to keep trimming it back up while running, its most likely ok.

[MarshMarlowe]

Understood. I've got a punch list of things to take care of before I can get the boat in the water, including a busted helm. Hopefully it will hold position the next time I run it! If it doesn't, is the unit rebuildable, or would a replacement be in order?

[throrope]

That's a nice rig. A good solid boat with a bomb proof outboard. When you get all sorted, you'll be a happy boater.

We have the same outboard and use a Universal M-Ywedge. It sits on the middle ram shaft and takes the weight off the trim. Its quick, compact and stores easy.

[MarshMarlowe]

Sorry for the late update. The motor holds position while running at speed. The trim still leaks down over a long period of time, but it doesn't appear to be any more than a nuisance.

[MarshMarlowe]

Update - the engine now leaks down much faster than before. Within an hour, the skeg is sitting on the concrete. Just to reiterate, I'm NOT seeing any trim fluid leaks anywhere. After doing some more internet research, I've found others with this problem and it seems to be caused by a failing check valve. My understanding is that the repair for this is costly and involved.

I haven't used the boat in a month or so, but the engine is not falling down while running. It's almost as if the increased pressure on the trim system helps hold the engine in place.

Could this hopefully be caused by something else? Thanks