Trim Pump proper pressure

Riverrat8428

Seaman Apprentice
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Feb 4, 2008
Messages
37
I have a OMC trim pump that I wonder what the proper up and down trim pressure should be. I think the assembly is refered to as the Permanent magnet type electric motor with a reverseing relays that are attached to the unit. The pump has been rebuild by a hydralic company. How ever the up pressure is only 1400 psi and down 800 psi. This pump assembly was used on the smaller outboards 2 cylinder models 55 hp and down... any infor would be helpful... I reading information that says the unit should have 2000 pounds....thanks
 

RRitt

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Joined
Mar 30, 2006
Messages
3,319
Re: Trim Pump proper pressure

it varies by year and design. You did not provide enough information to know either.

if it delivers and holds 1400psi then it should be good. by the time 2w motors with relays were introduced evinrude was all low pressure-high volume designs. gravity pulls the engine down and very little pressure is needed - only enough to prevent engine from kicking up in reverse.
 

Riverrat8428

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Feb 4, 2008
Messages
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Re: Trim Pump proper pressure

I do not know if you are familar with the racing motors that were built by omc in the mid 80s refered to as the SSt 45 engines they were two cylinder engines for an APBA tunnel boat class. The trim pumps that we used are now longer available but when they are working correctly they are fast and they index (no run on like the Mercury induction type motors) this makes a pricise adjustment on the trip, important for the diver. We had a leak down problem at the last race of the season and I wanted to know the proper pressure of the manufactures design. Here is what the pump looks like and I think I can remember other racers calling the pump a cobra pump. 986280%202.jpg 986280 OMC Cobra Stern Drive 4.3 5.0 5.8 Trim Tilt Motor Pump
 

RRitt

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Joined
Mar 30, 2006
Messages
3,319
Re: Trim Pump proper pressure

I am not familiar with specialty pumps. reverse engineering a hydraulic system and documenting a repair process is a significant undertaking. It takes a lot of rebuilds before you recoup the initial time and expense.

Nonetheless, pump pressure is set more or less the same as on an air compressor. the pump just pumps at full speed until a relief valve kicks open. The relief valve is almost always a precision chrome ball and a spring on a brass or aluminum seat. In a few cases it is a needle and a spring on a steel seat. There is usually a set screw that adjust the break open pressure. If not, you can often shim the spring. If you want to jack up the pressure, then go into the pump and find the relief valve. tighten up the spring to increase pressure. however, before going over 1500PSI you should make sure the fittings and hoses can take it.
 

Riverrat8428

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Feb 4, 2008
Messages
37
Re: Trim Pump proper pressure

Ok thanks for your responce... I will pass your information on to the hydralics people and see what they have to say. thanks again for your time.....Bill Hesson
 
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