I get a lot of questions about Piston Rings and Ring Gaps. Basic rule of thumb in machinest hand book is ring gap for cast iron rings should be .001 to .0015 for engines up to 1" bore, approx .65 to .70. Above that same rule applies up to 2" bore .0015 to .0025. Cast iron is one of the least expanding & contracting metal there is so ring gaps can be kept tight as possible in all liners, ABC, Chromed, Steel. Also on a lot of old & modern engines I always remove liner, invert it upside down & lap liner top flat on 320 to 400 grit emery paper taped down to really flat surface or a fine grit Diamond Hone Stone works well too. Approx. 40 to 60 % of the liners I check are not flat and will leak past liner top which could result in poor performance. Thanks & God Bless. Frank

I use 1/2 & 1/2 castor & Syn. with good results as with most engines I vary the % of oil & nitro depending on wheather it is a BB or plain bearing engine and what kind of engine make it is. But I run the older engines in my planes like ST.40-.60, OS .15-.35S, Mc Coy .35-.40, Johnson, Fox, K&B, and many more I started to use 1/2 & 1/2 oil mixes in my combat engines with good results and less destruction on hot days in matches. Hope that answers your question. Take care, Frank

Your method is great Mike as with new rings just remove shinny surface to help seat ring. Always go around liner contouring inside, not up & down. If one has to hone inside liner to true it up, the hone job could wear first ring out after initial run in so I replace first ring with new one after 15 to 30 minutes of run time.  Thin liners usually have more issues like early ST .40-.60 and K&B .40 as they tend to distort over time and could be egg shaped. In some cases I have straightened them, & send them out for hone & chrome job. Biggest problem with auto brake cylinder hones is always use the 3 stone hone with fine stones. But if liner to piston dimension exceeds .004 or more difference, piston slap will occur & ring probably never will seat. Keep cross hatch slight as too much just wears these tiny rings out. Dark areas inside liner says egged section, toss liner or rechrome. Always check ring fit to piston groove before installing ring and check ring in liner as well. Too loose of ring wears out ring groove ans a loss of power. I set ring gap at bottom of liner & top of stroke at .001. I lap liner top flat, gap ring to liner etc if one will send P&L to me at no extra charge except postage. Hope this helps. Take Care, Frank