Water in Oil and a damaged exhaust valve Mercruiser 120

[ToddyPond]

Hello all,

I have a 2.5 L Mercruiser (120 hp) from 85' that I just changed the oil on before the weekend's boating and have now discovered water in the oil. Not a lot, not even enough to raise the level on the dipstick to be noticable but it was in there. over the weekend, before discovering the oil problem i ran it for three days, probably for three hours a day or so. So last night I took the head and manifold off and looked for cracks in both (none that I can see) and checked the gaskets. The head gasket looks like crap and the manifold gasket doesn't look much better. There was surface rust in the third cylinder (and about a table spoon of water on the piston) that I cleaned out with paper towels and penetrating oil.

This cylinder also has bad exhaust valve (see picture). Could the exhaust valve damage be caused by water getting in the cylinder and causing it to heat and cool to quickly or over-pressurized? I didn't see any cracks in the cylinder walls so I think I may have lucked out and the cause is the head and manifold gaskets? Compression wasn't great on this cylinder last time I checked (100 or so) while the others were 130. Could water get by the pistons at that compression?



After reading the archives I know I should have done a leak down test before tearing into the motor, but the big question I have for you now is should I pull the motor and look under pistons just to make sure the block isn't cracked below the pistons (where I can't see now), or just put back together and do a leak down test?

Thanks for your time,

-Tom

 

[HT32BSX115]

Re: Water in Oil and a damaged exhaust valve Mercruiser 120

There was surface rust in the third cylinder (and about a table spoon of water on the piston)

Howdy,


Water in the cylinder is usually caused by a leaking riser gasket or cracked/rusted thru ex-manifold/elbow.

After reading the archives I know I should have done a leak down test before tearing into the motor,

Actually you should have pressure checked the cooling system FIRST. then maybe a compression/leak-down test.

water in the cyl can be a head gasket/cracked head but it's not as common as a cracked block (from freeze damage)

Do you live in cold country (in winter?)


I would look the intake/exhaust manifold AND riser over VERY closely. if there's a question, replace the manifold and riser.

If you don't see any block cracks, (on the outside) then it's not cracked (on the outside)...........

I would put it back together (and do a cooling system pressure check).


If it holds pressure, you're probably ok for a few more seasons. (although 100 PSI compression is pretty wimpy)

If I had your boat, I would probably start looking for a 3.0L engine to rebuild and install someday.....


Cheers,


Rick

 

[ToddyPond]

Re: Water in Oil and a damaged exhaust valve Mercruiser 120

Thanks for the info Rick,

I actually took a really close look at the head and cylinders again last night. No cracks. I also can't see any in the manifold on the outside or what I can see in the ports. I also sighted down the block and head and didn't notice any warping.

I think I figured out what I did (it was my fault). I pulled the engine a month ago and removed the exhaust elbow, and then never replaced the gasket between the manifold and elbow.

I would love a 3.0 L but in seeing that I bought the boat and trailer for $200 and I'm a graduate student on limited funds I'm going to run her into the ground (or the lake I guess).

I live in Maine, so yes I am in freeze country. I did winterize it correctly though.

I'll get the new gaskets and valves and report back.

 

[joewithaboat]

Re: Water in Oil and a damaged exhaust valve Mercruiser 120

Take that head and have it magnifluxed, surfaced, valve job, seals replaced, springs checked, etc. You dont want to just simply put new valves in it.

Good luck!

 

[ToddyPond]

Re: Water in Oil and a damaged exhaust valve Mercruiser 120

Take that head and have it magnifluxed, surfaced, valve job, seals replaced, springs checked, etc. You dont want to just simply put new valves in it.

Is the concern that it won't seat right? I am ordering new valves now, and can't seem to find the right specs in the manual to confirm I am ordering the right ones.

This is the site I am buying them from http://www.psepmarineparts.biz/store/mercruiser_internal_engine_exhaust_valves.htm.

My serial number is A469319. I think I need OEM part number 85803, is this right?

There are valves with a stem diameter .3415 and .3413. I need .3415 correct?

Thanks again for the help!

-Tom