Originally Posted by JKinTX
It's mainly to seat the ring(s). I got this from a guy that flew Rat in Texas a lot back in the 60's on into the early '70s. Wrap some electrical tape or masking tape around the crank threads before you chuck it up, take out the glow plug also. I used Marvel Mystery oil from the auto parts place to lube. It usually takes about 20 minutes or so on average.
Thanks for the Mystery Oil tip, JKinTX. Interesting that one takes the plug out. I thought it was the compression that splayed the ring out to wear in. However, that it works is the main thing. I have a drill press stand for an electric drill. I could rig something to gently hold engines still while running them. Come to think of it, I have a few other lapped piston motors needing break in. This sounds like a great and convenient way to break in, and be flight ready sooner.