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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3977
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Pearl. Kate here. I believe I may have a vapor lock in my

Customer Question

Hi Pearl. Kate here. I believe I may have a vapor lock in my trim system (1999 Yamaha 90 hp - C90 TLRX). I had to replace a wiper seal the other day and decided to go ahead and replace the o-rings as well. The motor raises fine. I have manually lowered and bled the system 100 times but it still has air at the very bottom when coming down. When trying to use the switch to lower it, it does fine until it gets to the trim pistons. They won't budge, even when applying pressure. You have to use the manual releif screw to get it to lower. I have opened them back up, removed all the fluid and replaced then closed it back up according to Yamaha's procedure. It still does the same thing. Any thoughts?
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Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.
Hello Kate, my name is***** will assist you.How have you checked the fluid level in the trim system?Does the trim system seem to bog down when it hits the trim pistons?
Customer: replied 1 year ago.
I check the fluid level by removing the reservoir cap and filling while holding the trim switch in the UP position until fluid starts to run out of the revservoir hole and the trim motor binds in the UP position. It does bog down as it hits the pistons and it won't budge them.
Expert:  Charles replied 1 year ago.
Ok, When you use the manual valve, will the motor come all the way to the bottom of the travel, or will it just hold on the tilt rams?Will the trim hold the motor in the up position while just sitting for a while?
Customer: replied 1 year ago.
Yes. It comes completely down when using the manual relief screw. Pushes the pistons right down but you can hear it gurgle still when it hits the bottom. The motor has been in the UP position without the lock on since yesterday and it is still holding fine today.
Expert:  Charles replied 1 year ago.
Ok, have you tried to lower the motor all the way down then hold the down trim button and see if the motor will load up or will it just continue to run?Did you have the pump removed when you did the work on the system?
Customer: replied 1 year ago.
I have tried that Charles. The motor just sits there and runs. I've even done it until the motor was getting pretty warm and I had to stop and let it cool off. The motor itself was never taken off.
Customer: replied 1 year ago.
To be clear... I can manually lower the motor, close off the relief and the motor raises right up like it should. I have also tried lowering it with the switch and holding the switch on after it hits the pistons and stops to no avail. It comes down fine until it hits the pistons
Expert:  Charles replied 1 year ago.
Did you remove the internal pistons from all 3 rods?
Customer: replied 1 year ago.
Not the tilt rod and piston. Just the two smaller trim pistons
Customer: replied 1 year ago.
Again, to be clear... I removed the two trim cylinders and rods to replace the o-rings on the cylinders. I did not take the cylinders off of the rods however.
Expert:  Charles replied 1 year ago.
Ok, the issue is going to be that one of those O-rings or the Teflon wiper somehow was pinched and is allowing the pressurized fluid to get past it. This is why you cant trim down, yet it will hold in the up position.
Customer: replied 1 year ago.
I kind of thought the same thing. That is why I took it completely back apart, inspected the wipers and the o-rings (all looked fine with no disfiguring like they had been pinched up), removed all of the fluid and replaced with fresh (LOTS of small bubbles). It did exactly the same thing. Stopped at the pistons.
Expert:  Charles replied 1 year ago.
Did you ever have the main piston out of the cylinder?Did you totally remove the manual relief valve?
Customer: replied 1 year ago.
Main piston? Not the TILT piston in the center if thats what you mean. I took the two trim cylinders and rods out of the port and starboard sides.The manual releif screw has never been out during this process (or as long as I have owned the motor-12 years)
Expert:  Charles replied 1 year ago.
And valve 39 did not come out?http://www.boats.net/parts/search/Yamaha/Outboard/1999/C90TLRX/POWER%20TRIM%20TILT%20ASSEMBLY/parts.htmlWere the parts Yamaha parts or aftermarket?
Customer: replied 1 year ago.
No sir. 39 did not come out. The parts were original Yamaha parts. I have to drive 40 minutes to the nearest Yamaha dealer to get them.
Expert:  Charles replied 1 year ago.
when you removed the tilt rods, did they slide on through the wiper seals easily or were they hard to get through?
Customer: replied 1 year ago.
A little pressure was needed but I wouldn't say it was hard to get them through. Just enough pressure that they would do there job correctly I would assume.
Expert:  Charles replied 1 year ago.
Was there any water in the system? Was the oil milky?
Customer: replied 1 year ago.
No. I had just taken it off the hose after changing the gear oil and water pump when I noticed there was a little oil around the wiper. Thought I woulkd address it while it was out of the water.
Customer: replied 1 year ago.
Have you ever heard of a trim system getting a vapor lock in it? I know its frustrating you. I've been going through everything for days now.
Expert:  Charles replied 1 year ago.
That is great maintenance. Can you trim it all the way up, put it on the lock. Then remove the snap ring from the end of the manual release, and take the manual release screw all the way out. Have your oil pan under it as it is going to lose some oil.No, I have never had a system lock in this way. There has to be a blown, pinched, o-ring or some debris in the system. We just need to find it.
Customer: replied 1 year ago.
I can give it a shot. I've never taken a relief screw all the way out so this will be a new one for me. LOL Its at my shop across the street. What should I do when I get the screw out?
Expert:  Charles replied 1 year ago.
Inspect everything for debris or cracked O-rings.
Customer: replied 1 year ago.
Will do. I'll report back shortly
Expert:  Charles replied 1 year ago.
Sounds good. Ill be here all day.
Expert:  Charles replied 1 year ago.
You can also upload pics of it here as well.
Customer: replied 1 year ago.
Hey Charles. Well, I have yet to get the snap ring off the relief screw. Its waaay up in there and it looks like I'm going to have to drill the motor mount out a little bit to be able to get the sr pliers in there. I did notice that the little taper screw that sits on the horizontal surface between the two trim cylinders had a tiny bit of oil around it. I cleaned it off well and trimmed the motor up and let it down manually a few times. The oil came back. I removed the screw and replaced the o-ring (which looked okay). Its not leaking any oil at all now and the gurgle has gotten less but its still there. I started watching it and listening closely for where it was coming from. I think its coming from the center tilt cylinder. Its not leaking anything at the wiper but could that be it? I never opened that one up but I guess the change in pressure after the new parts were put on the front two may have messed up an o-ring in there. I can get the yamaha parts for it tomorrow and take it apart. I probably have an aftermarket around here that would fit it but I'm not sure I want to chance it and mess it up worse.
Expert:  Charles replied 1 year ago.
Hello again Kate. With the screw i the center leaking, it could have also sucking air in the cylinder. I would not chance it with after market parts. There is a lot of pressure that is generated inside the cylinders. I dont think that a non Yamaha part would hold up.
Customer: replied 1 year ago.
I will bleed it a few more times and see if that helps then. I'll still try to get the relief screw out but wow! They make it tough! And I will get the parts for the tilt cylinder tomorrow and change it out. I will let you know how it goes. Thanks for your help.
Expert:  Charles replied 1 year ago.
Your very welcome. I should be on here all day tomorrow as well.