OMC Cobra Lower Unit Will Not Stay in the Up Position

[JJBoatr]

Tech info...1992 Four Winns, 190 Horizon, OMC Cobra 5.0/HO Ford(502APRAMK), Volvo SX style trim pump.

Bought the boat knowing that the starboard trim cylinder had a leak. Rebuilt both cylinders with genuine BRP seal kits. I thought this would fix the issue but it did not. The manual relief valve is tight, the system is free of air and the fluid is at the proper level. I also haven't found any other leaks. I have a seal kit on order for the valve body as this to me is the only logical next step. However, I have never had this problem and was wondering if anyone on here could share any applicable experience. I have heard that you shouldn't attempt the valve body rebuild because of complexity. If anyone has done this is this a true statement? Hydraulics are not complicated as long as you go slow and don't forget where to put check valve springs etc. I have some experience with rebuilding hydraulic components but it was for a fighter aircraft. So too Summarize:

Q1 - Any tips or pointers for this task?
Q2 - Is there another step in troubleshooting I should take before the valve body rebuild?
Q3 - Is it really as complex as some have said in other places?

All help will be appreciated on. Thank you

Mods...I realize there is another recent post that is similar in nature to mine and my intention is not to duplicate effort on this issue. However, I am further along in the trouble shooting and repair of this malfunction and if this post is effectively answered it will inform the other.

 

[JJBoatr]

Update...

I rebuilt the pump manifold and the lower unit is still slowly dropping on its own. The only position it will hold is full up. I'm at a loss. Where do I go next? Could one of the cylinders be bad despite having new seals in them? Could the manifold be worn beyond rebuilding fixing the problem? I rebuilt both the pump assembly and cylinders per my Seloc Manual. I cycled the system and I am 99% sure that the air has been bleed out. I really need some help as I don't want to guess at which component is bad when the pump assembly is $400 and cylinders are around $125 each.

 

[JJBoatr]

Update...

I performed a cylinder leak test by disconnecting the down lines(aft) on the cylinders while the leg was in the half up position. The starboard cylinder produced a drop of fluid about every 5 seconds. The port cylinder didn't drip at all. So after all of this it ended up being a bad cylinder even after rebuilding it. This is the same cylinder that had a leak when I got the boat. My assumption would be that it sucked some crud into the cylinder and it scored the cylinder and/or piston on the inside. Hope this thread can help someone out.

 

[ron3033]

JJ I wanted to PM you but don't know how. I just read your post on Volvo leak down of trim cylinders. I need to understand how you isolated the cylinders to see which was culprit. "I performed a cylinder leak test by disconnecting the down lines(aft) on the cylinders while the leg was in the half up position. " which is the down line the one on the back of the cylinder or the one under the plastic cover close to the silver rod?

My issue:1995 Four Winns 200 Horizon, 5 litre Ford, carb, Volvo Penta SX Cobra outdrive (light grey) The tag riveted on the drive says OMC Cobra Prod. No. 3868156 and Ratio 1.66.
This was about the time of OMC & Volvo Penta merger... I believe.
My outdrive sags down on the trailer about 2 inches in 4 to 5 days. I have no external leaks at the hose fittings or on the piston rods.
I have the old style pump (3855745 # 3855745 - interchanges with 3854030/3855744/3855334/986914/3587079 For most OMC/Volvo SX-Cobra Applications 1993 - 1998) looks like two cans stacked together with no plastic reservoir.
I bought a set of the new bi directional seals for the pistions. They are suppose to be better than the split seal set (Seal Kit; Tilt and Trim OMC Part Number 0985060)
I have been told it is the pump not the pistons, others say pistons not pump?? How can I determine which is the problem?
The place I bought the boat new from, changed owners & the new owners eventually lost the Four Winns dealership and their track record is horrible and there is a lot of unhappy folks. The boat is showroom condition, I was asked if it was a new boat last year. Unfortunately I Have not had it in the water this season due to surgery, but am hoping to get a bit of use here in our short summer season.
How can I determine the problem, as I do not have the $$$ to even chance the former dealer repair facility, nor feel comfortable. I do not have pressure guages, but have heard about capping lines?? To run the outdrive fully down, I need to get the trailer wheels up on wood planks to give it more clearance.
Thanks
ron3033

 

[GA_Boater]

JJBoatr

Ron, you should start a new thread.

Closed.