2011 F250 will not trim out under load

sutor623

Rear Admiral
Joined
May 23, 2011
Messages
4,087
Hey guys,

Motor is a 2011 F250TUR

I am working on this trim system. The unit will trim up and down as it is supposed to, and will not leak down when trimmed up and left up on the trailer.

This trim system was having issues before the motor was transferred owners. The shop that sold this motor rebuilt the trim system with new o-rings (supposedly).

While under load the motor will not trim out. If you trim the motor out and go under throttle the trim seems to hold. This lead me to believe that it was not the seals that were blown, but maybe a check valve somewhere in the unit??

I took the unit to my local Yamaha dealer (small town) and they said they didnt have any spanners to fit the trim caps. Soooooo I picked up a seal kit and a spanner wrench.

Got everything apart perfectly. The O-rings do in fact look good (they are still round and not flattened out.) I hadn't run the trim in a few days but when I pulled the drain plug the oil was bubbly and pressurized.

I drained it out and the oil is relatively dirty. Unit will get a good cleaning. I am going to put all new o-rings and seals in for good measure, but I feel like I am missing something. I checked all of the check balls and springs (in the pistons) and all seems well. I just don't want to put it all back together and have the same issue.

What else could be going on that would cause this? I have rebuilt quite a few trim units and have never run across this issue before.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,558
Breaker breaker. Anyone??

Trim is the first 20 degrees of tilt from vertical or where your engine 0 trim angle starts...realizing that most boat transoms have a 10* give or take angle allowing you to "tuck in" the lower unit. Once you exceed 20 degrees (a Mercury number) the overpressure valve opens and you are in a "tilt" configuration with a lighter breakpoint release valve. What the engine will do if say you are trimmed out to 30 degrees (for a number) and hammer down on the throttle, the lower unit will merely sink back to the high pressure position upper limit and should hold there.

If you are abiding by the above and still have a problem then yes you have something amiss.
 
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