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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4725
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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2003 yamaha F90 tilt trim slowly sinks down. Have added fluid

Customer Question

2003 yamaha F90 tilt trim slowly sinks down. Have added fluid and replaced the oil seal on the resivoir bolt. Took out the Manual relfief valve, didn't really see anything (smoking gun). Not sure what a bad one looks like. No oil on top of the ram. Used only 5 years in fresh water, garage kept. The unit has no signs of any corrosion. I understand the check valves are towards the back of the unit but not sure if they can be removed without taking the pump apart. Engine still slowly sinks down and won't stay in place. looking for help finding the cause and how to repair.
Submitted: 7 years ago.
Category: Boat
Expert:  Jeff G. replied 7 years ago.
I will be happy to assist you. If you have a question or need clarification please post back at any time.
Basically you did everything you could safely do. The hydraulic system is under pressure at all times and can be very dangerous to work on without the proper tools or training. It is best left to a qualified shop. It is one of the few things I don't recommend the boat owner try to repair.
You have an internal leak in the trim system, probably the up check valve. Other than draining and refilling the trim fluid there is little you can do. To remove the check valves and work on the system the proper procedure is to remove the engine from the boat, remove the trim system and disassemble on the bench and pressure test the valving.
Sorry I can't give you much more information or encouragement. Please post back with any additional questions.
Customer: replied 7 years ago.

A few comments. The procedure for removing the Tilt trim system does not seem that daunting. Open the manual relief valve to relieve pressure, the unit is help onto the engine with pins with circle clips, pull the top pin out to expose the wiring, disconnect the neg batt cable, disconnect the wires to the T&T remove the lower clip and pin. The up valve seems to accessible from the back and help in by a slotted screw if you look at the parts diagram for this engine.

I am not sure that all of the valve will come out if I pull the slotted screw, if it does then I can purchase the entire assembly under part number 67F-43802-00-00.
Expert:  Jeff G. replied 7 years ago.
If you want to do your own repairs you will need the up and down hydraulic pressure gauges to test the system through the manual relief port to find where the problem is. Without this you will need to totally disassemble, inspect and clean the valving. The valving you will want to get to is in the hydraulic pump unit.
You can not do the job without the proper OEM Yamaha service manual.
Pulling the trim unit is not the hardest part of the job, getting everything rebuilt and back together is.
It is a daunting repair to attempt, if you want to do it I will be glad to try and answer any questions and give you guidance.
Customer: replied 7 years ago.

I have the Yamaha OEM repair manual which does not tell a heck of a lot. I have spoken to a few tech's who really don't know a lot about taking apart T&T units. I can't really find anyone who services these T&T units. I have a parts listing and think if I can look inside i might get lucky see a smoking gun that points me to the problem. The valve is only $60.00 so I would just re-place it and make sure everything is clean, put in new O rings and filters wherever I take out. Take pictures along the way, lable parts and make notes. Can't see paying $600. for someone who has never taken one of these apart themselves.

On the otherhand, i might get it open and way.....this is tooo crazy looking.
Expert:  Jeff G. replied 7 years ago.
You don't have much to lose. Any time you open it up or blow through the ports, put a rag over the port so you can't get sprayed with the fluid. Even with the manual relief valve out there is still some pressure. Just be careful and label everything Take lots of pictures.

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