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Force trim pump???? 1991

M

mac_55

New member
boat 1963 comet 14"
engine 1975 70hp Chrysler
prop 13x21
trim tilt single cylinder 1991 70hp force

problem is trim/tilt does not work at WOT when engine is trimmed fully down. No leak down, no bleeding.
T
rim/tilt works when not moving and works when i slow down the boat to 30mph after that the trim tilt works great at all speeds

pump motor failing???
its like the pump isn't strong enough to lift the motor at wot but can do it a half speed and then has not problem after the initial lift to work properly
 
Jerryjerry05 said:
Those are a thing that if it works at all it should always work.
You check the oil level?
Click to expand...

Somebody messed with the pressure settings. I guess it's better to set the pressure low rather than overtighten and damage the valve seat. anyway, take pump off boat. put motor upside down in vice and remove four screws holding on valve body. one of the posts will have a set screw and locking nut. loosen nut and take out set screw using small allen wrench. Using a caliper measerue the drop from top of post down to spring. Calculate location of locking nut so that spring will be compressed 5/16". 70HP doesn't require a ton of PSI and the rough setting should put out 1200 or better on any valve body with healthy seats. So ,,, if that doesn't fix it then the regulator seat is probably damaged and will need to be replaced. If it is damaged then expect the cost of repair/replace to run from $100ish to $150ish. ebay is probably the best place. I haven't seen VB pop up on google or amazon yet.
 
just dawned on me i installed sx trim tabs this year and its been happening ever since so im thinking maybe there lifting the back of the boat and putting to much presure on the front of the boat for the trim motor to to handle , could that be a posibility ????
if not i got a good deal through kimpex mallory on a new pump assy or vb for cheap
 
mac_55 said:
just dawned on me i installed sx trim tabs this year and its been happening ever since so im thinking maybe there lifting the back of the boat and putting to much presure on the front of the boat for the trim motor to to handle , could that be a posibility ????
if not i got a good deal through kimpex mallory on a new pump assy or vb for cheap
Click to expand...

I don't think a Chrysler 70 can put out enough power to break open a healthy relief valve. The original 1991 should measure 1800-2400psi depending upon version. If the set screw has been overtightened then the seat might be damaged. I've had valve bodies that could not go over 500psi due to damaged seats. So as regards your existing valve body. if it lifts and holds without drifting down but can not hold trim then there is something wrong with the relief circuit.

The aftermarket valve bodies I have tested put out 1200psi. The pressure is adjusted by shims. I don't think you can increase the pressure by adding any more shims. It already has six in a design meant for three. If you change the spring then I think that will backfire on you too. The check valves are also patched to compensate for sloppy tolerances. I think if you jack up the psi then your check valves might burst.

what you need to do is get a 5000psi hydraulic gauge and hook it up to your trim up port. then run the system up and see how much psi you are getting. everything else is just throwing darts with a blindfold.
 
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