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Post by MCS on Jan 20, 2010 10:55:37 GMT -5
Does anyone have a new XL-925 piston ring, part number 69452, that they could measure? I'd like to know the uncompressed diameter of a new ring. Just lay it on a table and measure.
Thanks..
Craig
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Post by sugarcreeksaws on Jan 20, 2010 11:54:11 GMT -5
I get 2.105".
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Post by mikem on Jan 31, 2010 21:48:13 GMT -5
Does anyone have a new XL-925 piston ring, part number 69452, that they could measure? I'd like to know the uncompressed diameter of a new ring. Just lay it on a table and measure. Thanks.. Craig Craig.. this could be interesting ;D Do you think there is a direct correlation between ring fatigue and compression loss ?? Mike |
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Post by MCS on Feb 1, 2010 0:02:34 GMT -5
I think fatigue is a big contributor to lost compression and much more so than wear. In this picture there is a new and old 55537 ring.  The radial thickness is .085 on both the old and new ring so there isn't a lot of wear, but the uncompressed diameter shows a big difference. The new ring measures 2.200" and the old ring measures 2.120". That's an .080" change strictly due to fatigue. Bore diameter is 2.0625". The story is even worse on the 925 with thin rings. Same bore diameter. As Joe measured, a new 925 thin ring measured out at 2.105" but I have a used 925 ring that is bore diameter - it just falls in the cylinder. Note that a new thin ring (steel) would only have to be compressed .040" to fit in the bore where the 1/16" cast iron ring would be compressed .1375" so it is quite obvious there is less wall pressure. The thin rings are .024" which is about 3/8th the thickness of the cast iron rings. |
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Post by mikevan on Feb 1, 2010 6:44:17 GMT -5
Nice investigative work MCS - As I've never seen a ring on any engine that would just slide down into a cylinder, I'd have to wonder - Did someone put the wrong ring in it years ago?
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Post by mikem on Feb 1, 2010 14:34:34 GMT -5
If wear is not a major contributing factor, then are we to assume other factors are at work here, like:
1) heat(hard use,mis-adjusted carb, wrong fuel mix or whatever)
2) age(sitting unused on a shelf)
3) inferior material in the ring.
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