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

They’re the same. That said, somebody correct me if I’m not thinking this through properly, but if for some reason, one wanted to reverse the running direction of the M91, it would seem all that would be necessary would be to loosen the set screw and adjust the cam timing by ninety degrees of crank rotation, so the exhaust valve is open on the other side of top dead center, and spin it the other way. With only the single valve operated by the cam, and the intake valve suction operated, I would think that is all that would be required aside from cutting a reverse angled notch in the starter pulley to grab a rope wound the other way, or flipping the pulley over.