Am I losing my mind, or did I hear in a video about piston rings for these engines, that they’re supposed to use two rings? I think it was an unboxing video where replacement rings from banggood.com were mentioned. Another reference to someone replacing a ring said they installed a single ring in the lower groove.
My M91 has two grooves, but came with a single ring installed in the top groove. It’s fine right now, but looking toward the day when I need to re-ring it, I want to do the best set up.
Meanwhile, before I even got the engine, and after seeing the video mentioned above, I ordered a ten pack of rings for about six cents less than banggood gets for four.
There’s nothing magical about the rings. The eachine reference, replicated all over the net in ads for eachine piston rings, mentions flourogel. That’s actually the name of an entirely different product, a laboratory gel medium. The more correct nomenclature found throughout aircraft and other industries, is fluorine rubber o rings. Google that up in the 22 x 1 mm size, you’ll get lots of results far beyond the eachine etc engine reference.
I just wish I remembered who it was said two rings, or bottom groove, and why.