piston ring sizing

country boy 01 · Jan 20, 2011

ok i am currently working on a b-125 Allis Chalmers power unit now on this sit theres to different sizes of piston ring sizes 3 3/8 and 3 7/16 the size of the cylinder is 3 3/8 i am not new to rebuilding motors but i am a bit confused any help will be grateful

Anonymous-0 · Jan 20, 2011

Measure the cylinder is the first option, using telescoping piston gauges. Also clean off the top of the piston, and see if there is a 10, 20, or 30, stamped in the top of the piston. You might need the bigger ring, to make up for an over sized bore. If all else fails, order the bigger rings, and fit them by grinding the proper end gap clearance.

old · Jan 20, 2011

Are yo just putting in new rings or are you doing a total rebuild?? The way I understand it the 3-3/8 is the standard bore size of that engine and the 3-7/16 is the over bore size and that also means you need new sleeves to do that so if your keeping your old sleeves you need the smaller size rings if I understand your question right

rustred · Jan 20, 2011

your making me confused. what are you asking, if the 3 7/16 will fit in the 3 3/8 hole? i dont think so , so that just leaves whats left the 3 3/8. BUT it is possible to install the smaller rings on the bigger piston. AND i have seen it done on a 900 case tractor. the guy had to pull start it and it had blowby like crazy. found this out when i overhauled it. sounds like your on the green side so be careful.

country boy 01 · Jan 20, 2011

i plan on using the same sleeves and yes thats the size of cylinder 3 3/8

rustred · Jan 20, 2011

ya, you said that in your first post, that its 3 3/8, just dont know what your confused about.

Errin OH · Jan 20, 2011

If your planning on using the old sleeves you might find you can not gap standard rings properly as the wear in the cylinder is to much (low compression due to excessive end gap).

The 1/16th of an inch difference equates to roughly to .060 or 60 over. Bit much to be cheating with but do-able. I have bought 60 over rings and gap them in old cylinders before with good results (cheap fix).

Most enines that wear to the point they need rings usally go 30 over in the rebuild process.

Your call

country boy 01 · Jan 20, 2011

ok i figured it out just a dumb moment thanks

piston ring sizing

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