Another Smoking & Cruising Question

[Chief Engineer]

Originally Posted by Chief Engineer

We are not talking valve guides....but valve guide seals

I'll try to post a picture/diagram.

Valve Stem Seals

http://sagaforumet.com/yanmar-manual...JH3-manual.pdf

[Chief Engineer]

Valve Stem Seals

Originally Posted by Chief Engineer

Ther should be a hose running from the Valve Cover to the intake.....disconnect the hose from the air intake....start the engine......there is normally some internal pressure which will produce a small amount of vapour. If it is blowing out with force let me know and I will post the possible causes for that.

[Dockhead]

Originally Posted by Boracay

Given some indications that a PO may have not treated the engine right is it not possible that the bores have glazed?

My (internet expert!) research suggests that a turbocharged engine idled for a long time with the wrong oil would be a likely candidate...

I've thought about that. But glazed bores reduce compression besides allowing oil to get past the rings, right. I don't have the slightest sign of reduced compression; yesterday cranked her up with a brief flick of the key in 5 degrees C weather and no glow plug/air heater. Besides that, the boat has a generator and central heating, so not much reason for anyone to idle the main engine (charging batteries or making hot water for showers).

But still, I certainly can't afford to leave any stone unturned. How to check for glazed bores?

[Dockhead]

Originally Posted by Chief Engineer

Valve Stem Seals

I just performed this test.

Air (?) comes out of the valve cover when I take the hose off. A good flow of it. But it is not smoky and does not stink. What do you think about that? Wouldn't blow-by be combustion products -- smoky?

[Ex-Calif]

I don't think a leaky valve stem will necessarily pressurize the crankcase. There is positive pressure in the crankcase and a leaky stem would allow intake valve stem leaks to leak into the intake and then the cylinder. An exhaust valve stem leak would leak directly into the exhaust gas.

[Chief Engineer]

OK....I just did a Yanmar 2GM that had leaking valve seals.....it smoked like crazy because thee was way too much Crankcase Pressure. Re-did the seals. voila..no smoke....

[Dockhead]

Originally Posted by Chief Engineer

OK....I just did a Yanmar 2GM that had leaking valve seals.....it smoked like crazy because thee was way too much Crankcase Pressure. Re-did the seals. voila..no smoke....

OK, that's really interesting. How old was the 2GM? Hours?

I did as you suggested and pulled off the breather hose to check for gas and/or smoke. No smoke, but there was a pretty good flow of gas. What I didn't check was whether the engine was smoking when the hose was off (no crankcase pressure). My head was down below in the engine space, not at the exhaust. Maybe I'll try that next.

I guess you must have had bad valve guides? And not just seals? Otherwise how could a significant amount of gas get into the crankcase that way? Besides, the valve guides themselve are not subject to much pressure because they are not inside the combustion chamber -- only as much as there is exhaust back-pressure, which will be not too much when there's no turbo boost. Hmmm.

[Ex-Calif]

Correct and a non-turbo intake should be below ambient pressure.

I don't doubt the Chief's experience at all. He's got way more grease under his fingernails than me.

I also wouldn't bet the farm on valve seals but we do know that oil level is down, the engine is smoking and the oil has to be going somewhere.

There is no water in the oil or oil in the water. This should rule out head cracks and leaks, pump & engine mechanical seals, the heat exchanger and anywhere water and oil come together.

So where can oil get into the gas path? The head and valve train is the most obvious.

I skimmed the manual that Chief posted and did not see a wobble check. A wobble check is where you pull the valve cover, unload the valves and measure side to side play of the valves in the guides. The manual does provide valve to guide clearance but this can't be done with the cylinder head on the boat as the valve stems and the valve guides have to be measured separately.

A missing valve guide seal should be obvious once the cover is off and if it were me that's what I would be looking at soon.

[Sailmonkey]

I just have to ask, Is the smoke under load, at low idle, at high idle, or all three???

[Dockhead]

Originally Posted by Sailmonkey

I just have to ask, Is the smoke under load, at low idle, at high idle, or all three???

Right -- it smokes like a barbecue on startup, smokes at idle; smokes less when fully warmed up and under load.

We just tried it again with jury-rigged fuel, clean white diesel from a filling station out of a jerry can. It definitely smokes less. It seems almost normal now under load and fully warmed up.

This adds yet another twist.

[Chief Engineer]

Not necessarily compustion product...atomised oil

Originally Posted by Dockhead

I just performed this test.

Air (?) comes out of the valve cover when I take the hose off. A good flow of it. But it is not smoky and does not stink. What do you think about that? Wouldn't blow-by be combustion products -- smoky?

[S/V Antares]

New Fuel = Better? Sounds like someone may have accidently put some petrol (Gasoline) in the tank or seriously over used some alge or water/stabilizer. This would cause much earlier compustion than good ol' #2. and incomplete combustion and smoke. It does not take much. Sounds like you might want to get rid of the onboard fuel altogether or at least have it tested if there is a large quantity. IT is not uncommon for waste oil to be mixed in with the bunker fuel on large engines. This would not be good for a small diesel.

[Sailmonkey]

I'm out of ideas other than someone mixing motor oil in with the fuel............good luck

[Dockhead]

Originally Posted by Chief Engineer

Not necessarily compustion product...atomised oil

Is that what I'm looking for? Atomized from leaking valve stem seals? Seems to be clean air to me, but maybe I'll try holding some paper in the air stream.

[Chief Engineer]

Revisiting an old thread