RE: Wild (possibly heretical) notion
In reply to Digital Trucker, the Cox engines' piston is reasonably light because of the ball socket design. With a conventional wrist pin type steel piston, I don't think you can make the piston as light as the ball socket type, [which really hurts rpm potential]. The glowplug would really need to be countersunk deeply, the tool to wrench it would have to be thin.