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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3730
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Looking with a tilt cylinder on a Mercury outboard motor. It

Customer Question

Looking for whelp with a tilt cylinder on a Mercury outboard motor. It is a 2006 Mercury 150 hp Optimax. The cylinder was leaking from the bottom somewhere but after replacing the six o rings linking the tilt cylinder to the trim cylinders it was discovered the leak was coming out a hole at the bottom of the cylinder (it appears to be a vent or bleed hole but shouldnt be leaking fluid into the water at any case). Replaced the o rings in the tilt cylinder and still the fluid is running out the bottom of the cylinder.
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you today.

Is your engine a Pro XS or a regular Optimax?

Customer: replied 1 year ago.
It's a regular optimax
Expert:  Charles replied 1 year ago.


Would you say that the leak in located at the bottom of cylinder 11?

Customer: replied 1 year ago.
it is the tilt cylinder #11. If you look at the diagram it indicates a passage way from top to bottom. The bottom is apparently open and is leaking or venting air with fluid in it
Expert:  Charles replied 1 year ago.


What you are looking at is actually a milling passage during the manufacture of the cylinder, not a vent. The trim system is totally closed due to it being under water most of the time. Your cylinder is missing the little BB, that is normally in that hole. You can try to remove the cylinder, sand of the paint around the hole, get it really clean using acetone, then use a product called Marine-Tex to try and get the cylinder to seal up. The system produces over 1500 PSI when going up, so the repair may not hold. If it does not, you will need a new cylinder.

Customer: replied 1 year ago.
Is it possible that the BB could come out through the bottom due to pressure? It was leaking bad previously but worked fine until the fluid all went away. Is the BB available as a part number and then have the marine tex seal it in?
Expert:  Charles replied 1 year ago.

It is possible that just over time the BB was either knocked loose, corrosion got in the paint and ate the metal away, it was not installed totally when manufactured and just worked itself loose over the years.

There is no part number for it, even at my day job in a shop, we could not get this. I would either need to locate a BB and then try to use the Marine-Tex to hold it in, or replace the cylinder.

Customer: replied 1 year ago.
How far does the BB go in and how much Marine Tex do I use? Afraid to plug the passage other than the end which is leaking
Expert:  Charles replied 1 year ago.

The bb is just right there at the end. There are others on the system that you can see as well. Al you need to do is cover the end of the hole well to stop the leak.

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