yamaha trim limiter override

[chapparal21]

I have an 2002 ox66 I am in the lower keys and need to get through some pretty skinny water. The yamaha system limits how much I can raise my engine under load. How do I override this system? Scarring the bottom just ain`t right!!

[boats.net]

No there is no override, the two short hydraulic rams on power trim unit is the trim rams but once those rams are fully extended then it uses the tilt ram(center one) and it wont hold motor up under high speed will only up at very low speeds.

[chapparal21]

Must be a sensor or bypass that can be altered. This is one system not thought out well. You limit travel on i/o`s so not to damage universal joints with excessive angles. But outboards have no problem there. As long as you have water over intakes motor does not complain.

[jb123]

buy a jackplate and a bobs low water

[99yam40]

If the motor is setup properly on the boat it will start to cavitate and loose bite before running out of trim at planing speed. at least all of the rigs I have seen would. If you have a tunnel or pocket then jack plate is a must along with the low water pickup

[chapparal21]

It`s on a 24 foot center console out on a bracket. I can get my mercury`s up to clear bottom. Cavitation is not a problem , only need to go this high for a flat on entrance to home channel. Maybe I can feed tilt off of trim system or go to other motor at refit. Do all yamaha large engines have this preset?

[99yam40]

No there is no override, the two short hydraulic rams on power trim unit is the trim rams but once those rams are fully extended then it uses the tilt ram(center one) and it wont hold motor up under high speed will only up at very low speeds.

Did you not understand what he told you?

The 2 trim rams do the trimming and once they are fully extended then they cannot go any farther. If they are not fully extending then you have a problem and need to get it fixed.
Have you looked to see if they are extending completely?

The tilt ram will not lift the motor while under way, but will if you back off and relieve the pressure of forward push of prop. It just does not have the load capabilities in the hydraulics.

Is this problem while on plane or just idling?

I still think you have a setup problem if you cannot trim up enough to get the prop to start cavitation or slipping due to sucking air. Maybe need to change bracket angle with shims

[chapparal21]

I understand that the manual says there is a bypass to lower motor under load. I assume that is so someone wll not tilt motor and run out of water. But there are times when you are not getting home unless you can run that motor up , more than trim allows at full speed for a couple hundred feet. The boat is all factory set-up planes well and runs up to max rpm. My other boats 150 and 200 mercs will run at any angle under full load. I was just wondering if anyone had any idea of a way to stop fluid from bypassing and returning to resivoir. That size ram will hold that motor up under load. Thanks to all for the help.

[boats.net]

The manual bypass is the manual release valve on side of power trim unit so that you can raise or lower motor by hand in the event the electric trim motor fails to work. You might let your dealer look at to make sure trim is working properly.

[99yam40]

I give up!

Reread what was written to see if you can figure out what has been said or take to a Yamaha shop to let them check it out to see if the trim is functioning properly

[bumperfood]

The tilt/trim hydraulic system, is run from one source, the 12volt motor. It drives a positive displacement gear type pump. My understanding (others please jump in if you know better) of how it works is this. When operating the control to raise the engine the pump turns clockwise causing the pump to pump oil through a shuttle valve to first the trim pistons until they reach the end of their travel, the oil then overcomes a pressure relief valve and flows to the lift cylinder. The lift cylinder will eventually bottom out at the end of its travel and there will be another relief valve, one set at a lower pressure then the previous one, that that directs the excess oil into the reservoir. When no longer operating the control (neutral) the oil is still under pressure in the cylinders maintaining the engine at whatever height it was stopped at. It is held at this height by another pressure relief valve set at a pressure higher then the lift pressure relief valve. It is this pressure relief valve that keeps the engine up. When you have the engine running in forward gear you are putting enough pressure on the cylinder and to overcome the relief valve setting, and the engine lowers until either you slow down or the piston fully retracts and the engine now rests on the trim cylinders. The trim cylinders may not even have a relief valve, but if they do, it will be set high enough that the engine power will not be able to overcome it.
So now in answer to your question "How do I override this system?". You would have to install a higher value pressure relief valve in the tilt cylinder hold system. Unfortunately, I think this relief valve is located in the tilt cylinder piston and not in a return line to the reservoir, so that when the relieve valve opens oil is not returned to the reservoir tank, but rather just goes from one the bottom side of the piston to the top side via internal passages. I personally do not think it would be worth the effort.
Having said all that, there still may be away, if you have rejected the easiest option of a a jackplate as suggested by jb123. Get a couple pieces of hollow pipe that just fit over the trim cylinder rams, cut them to whatever length you deem correct, cap one end, and fill 1/2 way up with solder. When you get to the spot you need to raise the engine, stop the boat, raise the engine until you can slip them over the trim cylinder rams, then lower the engine onto these extensions. when you longer need shallow water drive, remove and store them 'till next time.