Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

With my M90 running so nominally about 30 hits/min with long coasting time & not exhibiting any frictional binding, tightness or squeaks, I'm reluctant to disturb it's current o-rings fitting...With such a close (prob < 0.001") piston to cyl bore clearance, an unfortunate "stack up" of production fitting tolerances could produce the occasional "tight" engine & with it's extremely hard steel cylinder liner & piston material used, a normal running wear self break-in won't happen. When/if O-ring replacement is needed, I'll sure try the single O-ring upgrade.