General Q about power trim systems....

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CharlieZulu

Petty Officer 2nd Class
Joined
Jun 2, 2008
Messages
122
I have to rebuild (I think) my trim system this winter, since my motor won't stay in the UP position anymore.... takes about 30mins to slowly come down.

Anyway, my question is this: why are these systems under full hydraulic pressure when the motor is DOWN? Intuitively (it seems to me) when the motor is UP and holding itself up there in the air, the system would be under a great deal of pressure in that position and not the other way around.

Clearly I don't "get" how these systems work (yet), and I guess all will become clear when I attack the problem is a month or so now that she is in the driveway.

Thanks in advance.
 
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Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: General Q about power trim systems....

Charlie, PTT systems need to secure the OB in any trim position you choose, against up and down movement, yet still allow travel if force is sufficiant.

Specifically, PTT unit must hold motor in position against the force of full throttle in FWD and full throttle in Reverse. Also, when you hit something the motor must tilt up.

A lot of PTT systems have control valves that will bypass oil, allowing OB movement, if the force is sufficient.
 
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CharlieZulu

Petty Officer 2nd Class
Joined
Jun 2, 2008
Messages
122
Re: General Q about power trim systems....

Thank you. Makes sense.

So what holds the motor in the up position? I can open the reservoir right up and check the fluid in this position.
 
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Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: General Q about power trim systems....

On a lot of Mercs, there is a check (or control) valve. This holds the motor in whatever spot you place it with the PTT. This valve is overpowered by either the PTT unit to change the position of the motor, or else when the motor strikes something.
 
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