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Old 22-07-2015, 21:55   #1
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Will A HeadGasket Solve This Problem?

yanmar 2qm20 raw water 1979 model
I noticed a bit of oil leaking down from what seemed to be the join between head and engine – I'm now satisfied that there is a very small amount of leakage from the oil and water galleys to the exterior of the engine. I'm also pretty satisfied that there is no leakage from the cylinders. I doubt whether the head has ever been off this engine. My guess is there has been some gradual corrosion of the gasket, but i am concerned whether there is also likely to be damage to the head and block surfaces – won't know 'til i pull the head off.
I'm wondering if anyone else has had a similiar problem, particularly whether a new head gasket can compensate for damage to the surfaces in the relatively unpressurised areas around the oil and water galleys.
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Old 22-07-2015, 22:36   #2
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Re: Will A HeadGasket Solve This Problem?

Install a new gasket as soon as you can. The important part of the gasket has an extra bead around the cylinder so you have time but don't wait too long. You could get oil in the water or vise versa before the cylinder starts leaking. It takes a bunch of corrosion to damage the head or block surface. The new gasket has a good bit of crush so it can handle a bit of roughness.
It's pretty cool that you saw this.
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Old 23-07-2015, 01:48   #3
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Re: Will A HeadGasket Solve This Problem?

Yeah - I was thinking they must have made a few improvements in gasket design since the engine was made, too. I blush to admit that i've been scratching my head over this problem for a few months - because theres no water in the oil, nor any loss of oil, i couldnt really work out what was going on. But while i was installing a new starter motor recently I noticed tiny bubbles where the oil markings were, which confirmed my suspicion that the galleys were leaking outwards. Time to roll up me sleeves.
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Old 23-07-2015, 02:03   #4
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Re: Will A HeadGasket Solve This Problem?

You could try re-torquing the head.

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Old 23-07-2015, 08:41   #5
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Re: Will A HeadGasket Solve This Problem?

yeah, when i was setting the tappets awhile ago I put a torque wrench on it, didnt budge. After 35 years undisturbed I wouldnt expect it to, either.
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Old 23-07-2015, 10:14   #6
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Re: Will A HeadGasket Solve This Problem?

A head gasket alone may or may not be the solution. Once the head is removed, have it taken to a machine shop and checked. It may need to be reworked a bit. THEN put a new head gasket on.
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Old 23-07-2015, 18:28   #7
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Re: Will A HeadGasket Solve This Problem?

What I would suggest is you find the appropriate head bolt sequence, and starting with number 1 , back it off about 30 degrees and then re- torque to specifications. Go around each in turn.
You may find that on re-tightening each one that they will go just a little further, but if you don't loosen them a little first they will not budge at all.

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Old 23-07-2015, 20:16   #8
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Re: Will A HeadGasket Solve This Problem?

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Originally Posted by boden36 View Post
What I would suggest is you find the appropriate head bolt sequence, and starting with number 1 , back it off about 30 degrees and then re- torque to specifications. Go around each in turn.
You may find that on re-tightening each one that they will go just a little further, but if you don't loosen them a little first they will not budge at all.

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What he said
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Old 24-07-2015, 00:43   #9
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Re: Will A HeadGasket Solve This Problem?

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Originally Posted by charliehows View Post
yanmar 2qm20 raw water 1979 model
I noticed a bit of oil leaking down from what seemed to be the join between head and engine – I'm now satisfied that there is a very small amount of leakage from the oil and water galleys to the exterior of the engine. I'm also pretty satisfied that there is no leakage from the cylinders. I doubt whether the head has ever been off this engine. My guess is there has been some gradual corrosion of the gasket, but i am concerned whether there is also likely to be damage to the head and block surfaces – won't know 'til i pull the head off.
I'm wondering if anyone else has had a similiar problem, particularly whether a new head gasket can compensate for damage to the surfaces in the relatively unpressurised areas around the oil and water galleys.
do the job properly, remove the head and have it surface ground before fitting a new gasket. the people who say les than that will not be with you at sea when the old gasket finally blows
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Old 24-07-2015, 01:12   #10
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Re: Will A HeadGasket Solve This Problem?

The oil galleys do not pass from head to block on the GM series. Yanmar uses exterior oil lines to feed the valve tappets and the camshaft. That line is mild steel and prone to rusting out.

Of course there could still be oil leaking from around the head from the pushrod holes where the oil drains back to the oil pan or from the crankcase breather.

If the breather is clogged oil will try to leak out just about anywhere it can.
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Old 24-07-2015, 01:26   #11
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Re: Will A HeadGasket Solve This Problem?

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The oil galleys do not pass from head to block on the GM series. Yanmar uses exterior oil lines to feed the valve tappets and the camshaft. That line is mild steel and prone to rusting out.

Of course there could still be oil leaking from around the head from the pushrod holes where the oil drains back to the oil pan or from the crankcase breather.

If the breather is clogged oil will try to leak out just about anywhere it can.
its a QM - bit older but yes the rocker feed is external and i just checked it because i put a new starter on a couple of weeks ago.
BUT - i haven't checked the oil breather - thanks for that. Heads coming off anyway. I'm pretty sure the oil is leaking from the oil drains, I just dont know why - but a blocked breather could be the cause.
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Old 24-07-2015, 09:13   #12
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Re: Will A HeadGasket Solve This Problem?

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Originally Posted by yajie boy View Post
do the job properly, remove the head and have it surface ground before fitting a new gasket. the people who say les than that will not be with you at sea when the old gasket finally blows
The reason for machining a cylinder head is not for the surface finish so much as it is for the flatness of the head. If your head is within tolerance you. could put it back on without machining.
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Old 24-07-2015, 09:21   #13
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Re: Will A HeadGasket Solve This Problem?

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The reason for machining a cylinder head is not for the surface finish so much as it is for the flatness of the head. If your head is within tolerance you. could put it back on without machining.
But how would he know that? Chuck
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Old 24-07-2015, 09:24   #14
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Re: Will A HeadGasket Solve This Problem?

Doubt they'd surface grind it; just fly-cut it, if it needs it, for flatness or to clean up erosion. Might as well do a valve job while the head is off. Check bore taper and oversize.
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Old 24-07-2015, 09:44   #15
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Re: Will A HeadGasket Solve This Problem?

If leaks occur, there can often be small pitting/corrosion at the leak site. It's hard to see but looks like discoloration on the head or block surface. Once you clean it up you can feel/see it well. It may only be few thousanths of an inch deep. It should be surfaced clean, but I did assemble one with that on the block side and it was never an issue afterwards. I know that engine is still going strong 15 years later. It may depend on the gasket type.
BTW, this engine had the corrosion from a minor compression/gasket leak. I never knew it until I took the head off for other reasons.
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