Yanmar YSE12

[Powergen75]

Hi fellow sailers, I have a Yanmar YSE12 which has a problem as follows;
Engine runs and sounds good but under higher revs and load oil is coming out of the exhaust with the cooling water and smoke. After running for some time the oil gets very hot and decides to blow out of the crankcase breather.
The yacht is new to us so the history is sketchy at best so I decided to strip the head off and take the piston out for inspection. All look in good condition as are the big end shells. The exhaust manifold looks dry of oil so my thoughts are now that oil is getting into the water system. Not sure why oil is blowing out of the crankcase breather?
I would welcome any advise or past experiences please.

Many thanks, Chris

[a64pilot]

Oil coming out of the crankcase breather almost always means excessively worn rings. It could be blow-by by excessively worn valve guides, but I've never seen that.

Almost everything your saying is classic excessive blow by the piston rings, excessive oil temp, smoke and oil in the exhaust.

Unless of course your running really very thin oil like maybe 5W-30 car oil or something

[westwinds]

Have you got any taper on the cylinder wall toward the top? It takes an inside micrometer to measure this, or is there a ridge you can feel at the top above the piston ring travel? I agree that this sounds like an excessive blow by situation where the combustion products are getting by the rings. This is caused by excessive taper in the upper cylinder wall probably caused by a bad injector putting too much diesel into the cylinder and causing excessive wear. Sounds like you have the engine out so take it to an automotive machine shop and have them measure the taper.

[a64pilot]

Could be glazed, but even a glazed cylinder usually causes worn rings, but you might get by with just a hone and new rings

Sailorchic,
You out there?

[sailorchic34]

Looks like the YSE12 is a raw water cooled engine... SO....

Most likely you have a bad head gasket, warped head or heaven forbid a cracked head. Normally oil out the breather is worn rings. But because you have oil out the exhaust too, that says you have a blown head gasket with a raw water cooled engine.

Now it could still be worn rings too. The poor girl method of checking for cylinder taper in a cylinder is to put a ring in the cylinder and measure the end gap with a feeler gauge at the top and bottom of the stroke, subtract the smaller reading from the larger then divide by PI (3.14159) and you have the taper/wear amount of the cylinder.

You check if the rings are good at bottom of bore by again measuring end gap and seeing if they are within service limit. New would be somewhere between 0.010" then 0.015", wear limit would be about 0.060" give or take a bit. Numbers are roughly correct.

But I've my money on a head gasket.

[Powergen75]

Thanks very much for your speedy replies. I'll check the bore, strip the head and get the injector tested this weekend. I'll keep you posted as to what I've found. Chris

[westwinds]

Originally Posted by sailorchic34

Looks like the YSE12 is a raw water cooled engine... SO....

Most likely you have a bad head gasket, warped head or heaven forbid a cracked head. Normally oil out the breather is worn rings. But because you have oil out the exhaust too, that says you have a blown head gasket with a raw water cooled engine... cylinder taper...But I've my money on a head gasket.

When you have the cylinder wear checked, also take the head in and have it tested for cracks. As Sailorchic points out, this is a raw water engine and so corrosion and mineral deposits are a concern. Mineral deposits cause hot spots that promote cracks. A blown head gasket happens a lot of times when the head gets warped so have them put a straight edge on it to see if it needs resurfacing. There will be some cost for head cleanup so the tests can be made, but not too much considering the cost of repairs. Have the machinist eyeball water passages for corrosion and check cylinder wear before you do any cleanup to see if you want to move forward. If there is cylinder wear requiring work, check on parts availability and costs.

[Powergen75]

Thanks again for all the advice, I'll keep you all posted on the progress, Chris