Tilt/Trim Problem

[LMITOUT]

Today after I arrived at the lake and got my boat ready to launch I walked down to the ramp to check it out, but when I went back to the boat I noticed the engine (Yamaha F90) had lowered almost all the way down. I raised it up again and watched it slowly fall back down. It appears there is something awry with the hydraulic tilt/trim assembly.

Thoughts on what specifically might be wrong and how much is it going to cost to fix?

[jac714]

Check the bypass valve, if it is loose this will happen.

[Valv]

Check the bypass valve, if it is loose this will happen.

x2.

[LMITOUT]

Checked the bypass valve and it was tight. I don't see any oil leaking from anywhere either.

The entire assembly looks easy to remove with pins on the top and bottom, although the prices I've found on the web for a new unit aren't as easy.

[Northlander]

Could it be as easy aS YOUR LOW ON HYDROLIC FLUID?

[LMITOUT]

IT'S FULL.

[kerryd15]

Not sure how the bypass is set up on yours but my merc has some orings on the bypass, could be an oring. Also on mine, there is a small oring way at the tip of the bypass plug. Some how that tip was broke off up inside there. I know different brand but may be similar.

[LMITOUT]

Something else that I determined after examining a drawing of the exploded view of the tilt/trim assembly is that it only loses pressure when in the tilt portion of the lift range. When the motor is lower in the range of movement (trim function) the hydraulic pressure is solid and will not allow the engine to fall.

I would to try fixing it myself but after looking at the drawing I think I'll see what the boat mechanic has to say.

[marine_man]

Sounds to me like a check valve or o-ring went internal to the unit...

marine_man

[LMITOUT]

Have you ever had one apart?

[Valv]

There should be 3 pistons, the tall one is for the tilt, the 2 small ones for the trim.

[LMITOUT]

Mine just has one piston rod, but internally there are two pistons that apply pressure to that rod...one for tilt and one for trim.

I have the schematic for the internals and just got back in from taking the top off but I couldn't get much further than pulling out the rod and one piston that is attached to it. Didn't see anything visibly wrong, but I'm not sure how to get the "guts" out...and not sure I want to.

[leech~~]

Something else that I determined after examining a drawing of the exploded view of the tilt/trim assembly is that it only loses pressure when in the tilt portion of the lift range. When the motor is lower in the range of movement (trim function) the hydraulic pressure is solid and will not allow the engine to fall.

I would to try fixing it myself but after looking at the drawing I think I'll see what the boat mechanic has to say.

It does seem kind of odd that when full out holding the motor up it has less pressure but it does. At full out the fluid in the piston has more room to expand and when full in the fluid has less room and is compressed. Bring it all the way up and put it in lock if you have one or put a board under it and bring it down a bit. Then the pressure will be less and you can undo the plug to drain it and work on it!

[LMITOUT]

I've already got it on the bench.

[LMITOUT]

Assembly #2 is what I extracted from the cylinder. Not sure how the rest of it comes out. Magic I think.