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Piston ring gap

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AJW28/02/2019 12:51:08
288 forum posts
117 photos

I shall be fitting the rings to my Centaur engine shortly and am wondering about the gap that I should aim for as the construction drawings don't give this a mention.

It's only got two compression rings in a 1.5 inch bore, is there a recommended figure?


MichaelR28/02/2019 14:13:24
370 forum posts
75 photos

I gave the rings on my Centaur a gap of 0.002 the engine runs well with this gap. Mike.

Howard Lewis28/02/2019 15:41:22
3149 forum posts
2 photos

On the basis of 0.001" per inch of diameter, 0.0015" to 0.002" should be correct.

Wider gaps will increase blowby, and tend to reduce compression, particularly when starting ( When time for leakage is greatest ). Don't go below the minimum,or the ring ends may butt. That will lead to broken rings and bore damage.

Try to make the rings a snug, sliding fit in the grooves, again, to reduce leakage and blowby.

Things will improve as the rings bed to the bores and the ring grooves.After a couple of minutes, gradually increase the load on the engine, to help the rings to bed.

Don't let it run fast, off load,, for long periods. This will tend to glaze the bores and rings, which will cause oil carry over into the exhaust, and blowby.



AJW28/02/2019 19:27:08
288 forum posts
117 photos

Thanks for the info, I thought I had read a thou per inch bore but couldn't find it.

I cheated and bought my rings but for a 38mm bore, I think they were for a chainsaw engine so my Centaur was bored 38mm instead of 1 1/2 inch to suit.

When fitting the rings this afternoon I found the that without touching them gave a 0.010 gap! Not quite what I had in mind.

I have assembled the engine with the (large) gaps opposite each other and will see what happens.

I guess the rings I got hold of are 'plug and go'!?

Might have to find some others or make my own.


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