LMITOUT Posted September 16, 2012 Share Posted September 16, 2012 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? Quote Link to comment Share on other sites More sharing options...
jac714 Posted September 16, 2012 Share Posted September 16, 2012 Check the bypass valve, if it is loose this will happen. Quote Link to comment Share on other sites More sharing options...
Valv Posted September 16, 2012 Share Posted September 16, 2012 Check the bypass valve, if it is loose this will happen. x2. Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 16, 2012 Author Share Posted September 16, 2012 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. Quote Link to comment Share on other sites More sharing options...
Northlander Posted September 16, 2012 Share Posted September 16, 2012 Could it be as easy aS YOUR LOW ON HYDROLIC FLUID? Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 16, 2012 Author Share Posted September 16, 2012 IT'S FULL. Quote Link to comment Share on other sites More sharing options...
kerryd15 Posted September 17, 2012 Share Posted September 17, 2012 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. Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 17, 2012 Author Share Posted September 17, 2012 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. Quote Link to comment Share on other sites More sharing options...
marine_man Posted September 17, 2012 Share Posted September 17, 2012 Sounds to me like a check valve or o-ring went internal to the unit...marine_man Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 18, 2012 Author Share Posted September 18, 2012 Have you ever had one apart? Quote Link to comment Share on other sites More sharing options...
Valv Posted September 18, 2012 Share Posted September 18, 2012 There should be 3 pistons, the tall one is for the tilt, the 2 small ones for the trim. Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 18, 2012 Author Share Posted September 18, 2012 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. Quote Link to comment Share on other sites More sharing options...
leech~~ Posted September 18, 2012 Share Posted September 18, 2012 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! Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 18, 2012 Author Share Posted September 18, 2012 I've already got it on the bench. Quote Link to comment Share on other sites More sharing options...
LMITOUT Posted September 19, 2012 Author Share Posted September 19, 2012 Assembly #2 is what I extracted from the cylinder. Not sure how the rest of it comes out. Magic I think. Quote Link to comment Share on other sites More sharing options...
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