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Old 11-11-2019, 11:47   #1
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Piston Ring size for replacement?

Hello all,

I received a ton of useful help from fellow sailors through this forum last time I posted my issues with a Yanmar 4jh2te.

This time around I just have 2 questions to solve my next step in the engine rebuild.

I have measured my bores after honing them to remove pitting from water damage the engine received & I'm always within 3.2283-3.2295 as the manufacturer states to be "Standard", the stated wear limit is 3.2307(82.06mm).

Yanmar sells the standard rings and the OS 0.25 Rings.

Should I install the standard ones as I'm not exceeding 3.2295?
As of my understanding, the standard rings are for bores withing the 3.2283 - 3.2295 range and the OS 0.25 for the 3.2295-3.2307 range.

Thanks again,
Isaak
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Old 11-11-2019, 12:33   #2
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Re: Piston Ring size for replacement?

I'd stay with new std. size rings. The +.25 rings would be too tight. Make sure you check the ring gap before installing on the pistons.
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Old 11-11-2019, 15:07   #3
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Re: Piston Ring size for replacement?

Yes ring gap will tell the tale, the oversize rings would probably need excessive filing.
If you put in rings that are too tight, they will break.
Sorry if I insult but you check ring gap by using a piston to push rings to near the top and then measure gap with a feeler gauge, the piston is needed to keep the rings perfectly flat.
Measure each ring in the correct hole.

There are usually two different standards for an engine, one is meant for new parts, and the other is the wear limit. You may still meet new part criteria.
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Old 11-11-2019, 19:43   #4
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Re: Piston Ring size for replacement?

Without the manual in front of me, it is difficult to tell, but I believe you are mixing apples and oranges.....

You speak of standard bore dimensions as 3.228" - 3.229"...INCHES

But you speak of the oversize piston & rings as 0.25, but you don't dimension it....is it inches or mm? Almost for sure it is not .25 inches oversize...it is more likely .25 mm which is about 0.010".

In any event, a 0.010" oversize piston ring will never work in a standard bore or even one worn one or two thousandths. For that ring to work you need to bore the cylinders 0.010" oversize.

Use standard rings in the bores which you have.

DougR
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Old 12-11-2019, 09:21   #5
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Re: Piston Ring size for replacement?

Quote:
Originally Posted by DougR View Post
Without the manual in front of me, it is difficult to tell, but I believe you are mixing apples and oranges.....

You speak of standard bore dimensions as 3.228" - 3.229"...INCHES

But you speak of the oversize piston & rings as 0.25, but you don't dimension it....is it inches or mm? Almost for sure it is not .25 inches oversize...it is more likely .25 mm which is about 0.010".

In any event, a 0.010" oversize piston ring will never work in a standard bore or even one worn one or two thousandths. For that ring to work you need to bore the cylinders 0.010" oversize.

Use standard rings in the bores which you have.

DougR
this guy got it right! LMAO
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