When I first figured out how a 360 motor worked I was kinda surprised too. I mean it seems like an awefull lot of reciprocating mass to be jumping around together! But that's how it is... There is a separate coutnerbalance shaft rotating (opposite direction I believe...) with some offset mass on it to quell the vibs. Check out the old bonnies and nortons at idle that didn't have that! The front wheel almost hopped off the ground
