special potions to free piston rings?

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mattnj

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Ok. So my yanmar 3cyl is now running nicely....turned out the exhaust was totally blocked and full of carbon.
it has only run 70hours and is a 2006 engine. Done a lot of standing around.

just had it compression tested and got 600/600/350psi
so one cylinder is down. Oil and water is spotless but a fair amount coming out the breather.....

I know its been sitting for years since the exhaust was blocked so reckon the rings are gummed up on that cylinder

any crazy ideas of mixtures to pour in and leave to soak to free them up before I strip it down!
 
Always check the easy things first! Make sure the tappets are at their correct values.

Did the person doing the compression test do a second one with oil down the bores? This is standard when a low value is found: the oil provides a temporary seal at the rings, increasing the reading to somewhere closer to the correct value. If oil makes no difference the leak is in the valves, a crack, poor gasket, etc.
 
Diesel is as good as anything to try to unstick a ring..... Rill the bore, leave it for winter.... dry it out and give it a go in the spring. You could try topping up occasionally.

Failing that its a strip down job. If you are lucky, with use it will improve.
 
mattnj said:
I know its been sitting for years since the exhaust was blocked so reckon the rings are gummed up on that cylinder

any crazy ideas of mixtures to pour in and leave to soak to free them up before I strip it down!
Click to expand...

50/50 mix of engine oil and paraffin has been known to work.
 
I would do as Vyv suggests as a first step, if there was a lot of carbon in the exhaust manifold it is possible the exhaust valve on the low cylinder is also carboned up. If it is the rings put some KRoil into the cylinder and leave it for a couple of days and it will creep under the carbon deposits and loosen it.
 
vyv_cox said:
Always check the easy things first! Make sure the tappets are at their correct values.

Did the person doing the compression test do a second one with oil down the bores? This is standard when a low value is found: the oil provides a temporary seal at the rings, increasing the reading to somewhere closer to the correct value. If oil makes no difference the leak is in the valves, a crack, poor gasket, etc.
Click to expand...

Did try with oil. No noticable difference.
Its not leaking between cylinders and not into oil or water, it is puffing nicely out the breathers so must be going past rings? Unless its scored? The guy looking at it didnt think I would get 300psi if leaking past a valve.

I will stick some diesel in there for a day or so, then empty and then try ragging it hard for an hour. That is after checking the tappets.
 
If its been sitting for a long time then at least some of the valves will have been 'open' for that time. The open valves may well have got a little corrosion on the seat or valve stem causing them to stick or leak. If after the test which Vyv suggested and you followed it is unlikely to be rings/bores.
 
galadriel said:
If its been sitting for a long time then at least some of the valves will have been 'open' for that time. The open valves may well have got a little corrosion on the seat or valve stem causing them to stick or leak. If after the test which Vyv suggested and you followed it is unlikely to be rings/bores.
Click to expand...

I am a little confused...surely if a valve was leaking it would be leaking either into the exhaust or inlet manifold.....so it wouldnt be smoking out the breathers?
 
vyv_cox said:
Always check the easy things first! Make sure the tappets are at their correct values.

Did the person doing the compression test do a second one with oil down the bores? This is standard when a low value is found: the oil provides a temporary seal at the rings, increasing the reading to somewhere closer to the correct value. If oil makes no difference the leak is in the valves, a crack, poor gasket, etc.
Click to expand...

Your assumption (stuck rings) may be invalid - you need to do the checks outlined by Vyv before committing any further energy to solving the problem.
As already suggested diesel is probably the most effective degummer. but you'll probably need to have the head off. If one of the raw-water cooled 3GMs you need to check the head-gasket between #3 cylinder and the water way - it's a favourite place to go and even more likely if the engine has been run with a blocked injection elbow.
If you need a new head-gasket use Marine Power to supply - their prices aren't as crazy as most other Yanmar agents.
 
mattnj said:
I am a little confused...surely if a valve was leaking it would be leaking either into the exhaust or inlet manifold.....so it wouldnt be smoking out the breathers?
Click to expand...


Smoke or steam from the breather? Which should, incidentally, go to the inlet manifold.

Evidence increasingly pointing to gasket leak. And possible bore corrosion.

I ran a 2GM for about 1700 hours in that condition - though it wasn't producing much power at the end of its life. The cost of strip/rebore/rebuild (with new parts) was more than a replacement 3YM.
 
Last edited:
charles_reed said:
Smoke or steam from the breather? Which should, incidentally, go to the inlet manifold.

Evidence increasingly pointing to gasket leak. And possible bore corrosion.

I ran a 2GM for about 1700 hours in that condition - though it wasn't producing much power at the end of its life. The cost of strip/rebore/rebuild (with new parts) was more than a replacement 3YM.
Click to expand...

Smoke and steam from the breather can also be valve guides.
I had this on a bike, classic symptom was lots of white smoke due to oil sucked in when you shut the throttle. Obviously that won't be quite the same on a disease-all.
 
charles_reed said:
Smoke or steam from the breather? Which should, incidentally, go to the inlet manifold.

Evidence increasingly pointing to gasket leak. And possible bore corrosion.

I ran a 2GM for about 1700 hours in that condition - though it wasn't producing much power at the end of its life. The cost of strip/rebore/rebuild (with new parts) was more than a replacement 3YM.
Click to expand...

Ok, the chap tried a compression test with/without oil it was basically the same values, although I can never be 100% sure enough oil went in, I wasn't there watching!
It is white smoke from breather, not terrible, but not quite right!

The breather is off the rocker cover and goes to atmosphere (its a generator, not running in a boat cabin!)

I am still confused by the suggestions here, obviously due to my lack of knowledge....but I don't see how it can be a gasket leak? Surely it could only leak to another cylinder (that would screw up the other cylinders compression?) or to the water (not happening) or the oil (not happening) or to the outside world (I would see/hear that?) hence the reason to think rings/bore.

I have given in to the fact that it need to be stripped down, I am just looking for a few crazy ideas to try before I commit to that.
Will check the valve clearances and pour some heated diesel in the #1 cylinder next!

Thanks
 
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