Refurb or replace anegine, or leave well alone?

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peter2407

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I have a Yanmar 3GM30 FW engine that there was an issue with year before last, which actually turned out to be a heavily coked up exhaust elbow. As part of the process of elimination, I did pressure tests that showed that the central cylinder has pressure readings of 50% of the other two, the other two reading as expected as per the spec (forget the numbers involved).

I am taking the boat out of the water to do some maintenance work, and was thinking about sorting the engine.

Other than the odd starting problem due to weak batteries, generally the engine is reliable. The reason for thinking about this is simply down to getting the most out of the time ashore.

What would you do?
 
was it rings or valve stems causing the exhaust problem or was it over cooling due to a faulty thermastat, or maybe you dont rev it hard enough
I'd do another compression test first to be sure of your figures because I'd think if one cylinder was down it would affect reliability
assertain as best as you can if its head or rings, for example a broken ring will very likely damage the bore so you'd end up having the engine rebored
if you can do the test, check results then put oil in the bore to find out if the compression goes up if it does then its rings or piston if not you have a head to sort out
 
Before taking off the head I would take off the rocker cover and slowly turn over by hand to check rockers valve springs and tappet clearances this will cost nothing and may just lead to an easy fix .
 
A starting point would be to make sure that the valve clearances were correct - a valve that is a bit tight on the central cylinder will give it a low pressure reading.

I wouldnt even contemplate a replace in the situation you describe . But personally the low reading would niggle as something that wasnt quite right so I would lift the cylinder head, an easy diy job, and do the valves and valve seals. If there was nothing obviously wrong there then its time to check the cylinder bores tro see if there is damage or maybe worn rings. Maybe all that is needed is glaze busting. Either way, remedial action will be way cheaper than replace and if you do it yourself will not be expensive at all.

Maybe its me, but I would be looking at that problem as an interesting project to brighten up the winter.
 
birdseye said:
A starting point would be to make sure that the valve clearances were correct - a valve that is a bit tight on the central cylinder will give it a low pressure reading.

I wouldnt even contemplate a replace in the situation you describe . But personally the low reading would niggle as something that wasnt quite right so I would lift the cylinder head, an easy diy job, and do the valves and valve seals. If there was nothing obviously wrong there then its time to check the cylinder bores tro see if there is damage or maybe worn rings. Maybe all that is needed is glaze busting. Either way, remedial action will be way cheaper than replace and if you do it yourself will not be expensive at all.

Maybe its me, but I would be looking at that problem as an interesting project to brighten up the winter.
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+1,but would add that if gone that far not so much more work if you can get to the sump to change the piston rings?
 
The coked up exhaust was possibly a symptom of the low compression as the engine will be exhausting unburnt fuel possibly a tight tappet but valve or seat may have suffered from running like that personally I'd take off the head & check valves & seats then if nothing obvious I'd glaze bust it & fit new rings glaze busting alone is a waste of time IMHO
A good opportunity to clean & paint the engine while its out!
 
peter2407 said:
Refurb or replace an egine, or leave well alone?
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I have had two engines refurbished.
In both cases, the refurb was about 35-40% of the cost of a new engine.
Both engines failed and were declared beyond economic repair within 4 years of the refurbishment.
Was the refurbishment value for money?
I don't feel it was.
Not going down the refurbishment road ever again.

Your 'problems' seem relatively minor and I would leave well alone.
Just my £0.02
 
OR4751 said:
I have had two engines refurbished.
In both cases, the refurb was about 35-40% of the cost of a new engine.
Both engines failed and were declared beyond economic repair within 4 years of the refurbishment.
Was the refurbishment value for money?
I don't feel it was.
Not going down the refurbishment road ever again.

Your 'problems' seem relatively minor and I would leave well alone.
Just my £0.02
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I think you were ripped off!
 
I find it hard to believe people are suggesting the op puts to sea with an engine that isn't 100%.
Can't exactly call the RAC or AA when the engine fails & your drifting onto a rocky Lee shore!
ohhh I forgot that's what the RNLI is for!!!!
If it's half broke get it fixed before your life depends on it! It isn't going to heal up
IMHO of course
 
Beamishken said:
I find it hard to believe people are suggesting the op puts to sea with an engine that isn't 100%.
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I guess it's a mindset difference between sailors and motorboaters. Even though we do tend to rely on our engines more than most will admit, most of the time if it fails (and I've experienced that at least half a dozen times) we're not left helpless in the same way as a single-engined mobo would be.

Pete
 
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