Jim, specifically, in this case, we are talking about gasoline engine break-in, not glo or ABC/AAC/ringed glo motors.

Jett is correct in his assertions about the non-ringed ABC and AAC engines. They have a lot of clearance along the bore and then close up near the top for better sealing during combustion. But, remember. . these glo engines use 20%!!! oil content in the fuel, not 1-2.5% (depending on pre-mix ratio) like our gassers use. Things get a tad more critical in our case, I think.