Oil out of exhaust?

[Harry P]

After a sail this week I was maneuvering around the pontoons in the marina and my engine, a twenty year old Yanmar 2GMF, developed a quite noticeable knocking sound. Strangely this was only in forward gear and only at higher revs, in reverse or at lower revs (forwards or backwards) this didn't happen. After tying up I tried it again with the same results. A guy who had serviced my engine in the past, looked at it the next day and couldn't get it to make the knocking sounds although he noticed the screw at the top of the secondary filter had vibrated loose and on tightening it up the engine ran smoother. He also checked the oil level, which was fine.

I went to the boat today and tried to see if I could still hear the knocking sounds, I couldn't, and it seems to be running very nicely, as always. I looked at the exhaust emissions and noticed floating in the water about a teaspoon sized glob of black oil. I hadn't seen it coming out of my exhaust but it seemed likely that's where it was from. A few minutes later there was another one but yet again I can't be 100% sure it was from my exhaust. I think the exhaust fumes are starting to appear bluer that the usual white and I think I can smell burning oil from them. Perhaps I'm getting paranoid about it.

Everything else appears normal.

Any thoughts on this?

Cheers

 

[CAPTAIN FANTASTIC]

Oil from the exhaust valve indicates that oil from the rocker head is passing through to the exhaust port either from the valve seal or stem, or valve guide/bush as result or wear and tear; not too serious, just engine getting old perhaps.

When the engine gets hot, and at higher revs, it is more likely for oil to seep through, as the bush is normally brass alloy based material with higher expansion (in general, not sure on the Yanmar)

 

[pampas]

possible oil gallery burnt though into exhaust Common fault), but check everything first

 

[Zagato]

Anything to do with the exhaust elbow corroding I wonder

Thread here for the 2GM20 exhaust elbow if it helps...

http://www.ybw.com/forums/showthread.php?t=338375

 

[pampas]

further to my reply, remove the exhaust ststem and look up the hole to see if one (Or both) are oily. where its likely to go is, on the aft cylinder, look carefully at the fwd, wall, look for any cracks , and the aft wall for the fwd, cylinder, thats the firts place I would look at,

Then a compression test. Trust this helps.

 

[pmyatt]

After a sail this week I was maneuvering around the pontoons in the marina and my engine, a twenty year old Yanmar 2GMF, developed a quite noticeable knocking sound. Strangely this was only in forward gear and only at higher revs, in reverse or at lower revs (forwards or backwards) this didn't happen. After tying up I tried it again with the same results. A guy who had serviced my engine in the past, looked at it the next day and couldn't get it to make the knocking sounds although he noticed the screw at the top of the secondary filter had vibrated loose and on tightening it up the engine ran smoother. He also checked the oil level, which was fine.

I went to the boat today and tried to see if I could still hear the knocking sounds, I couldn't, and it seems to be running very nicely, as always. I looked at the exhaust emissions and noticed floating in the water about a teaspoon sized glob of black oil. I hadn't seen it coming out of my exhaust but it seemed likely that's where it was from. A few minutes later there was another one but yet again I can't be 100% sure it was from my exhaust. I think the exhaust fumes are starting to appear bluer that the usual white and I think I can smell burning oil from them. Perhaps I'm getting paranoid about it.

Everything else appears normal.

Any thoughts on this?

Cheers

Was the engine in gear when you were doing your test? Suggest you get the engine properly warm, and then try some tests at about 3000 RPM in both ahead and astern to see what happens - a couple of minutes each way should be enough.

 

[simonfraser]

My 14 yr old mower ! blew blue smoke recently, used plenty of oil, blown head gasket.

 

[theoldsalt]

I had a knocking apparently from my engine a couple of years ago. It turned out to be a loose anode on the prop shaft. The anode was sliding along the shaft and hitting the hull when going astern and the 'P' bracket when going ahead.