Many 2 cycle engines are sold with plain steel bearings instead of using stainless steel. The reason that I hear the most is that stainless steel is softer and doesn't make for as good a material for bearings. The problem is, regular steel bearings tend to corrode quickly in glow fuel applications. There are many favorite ways of tryign to prevent this using different types of after run oil etc., but I don't have much luck with this. If you live in a very humid climate and store airplanes in the basement like I do, you might have as much trouble too. If you are in a drier climate and don't have to store in a damp place, then you might get much better results.

Piston rings will eventually need replacement, but with good care in breaking in, running without setting the engine too lean and most of all, not running with corroded bearings, they should last many hundreds of flights. If you let the bearings get rusty, that stuff creates a polishing rouge when mixed with fuel and it just wears away at the piston, ring and cylinder liner (mostly the ring suffers).