This is a great explanation. I'd add one small clarification: > Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cyc

This is a great explanation. I'd add one small clarification: > Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cycling back around The firing of other pistons helps, but really, momentum alone is sufficient. There are tons of single-cylinder, 4 stroke motorcycle, scooter, and off-highway engines out there.