Balance shaft A shaft designed so that, as it rotates, it vibrates in a way that reduces or cancels some of the vibration produced by an engine. Not essential to an engine's operation, balance shafts are nonetheless becoming increasingly common as a means of engine refinement. Balance-shafted four-cylinder engines use two shafts turning in opposite directions on either side of the engine's crankshaft. A single balance shaft is used when fitted to three-cylinder and V-6 engines.
Sorry, Ninjabeater but you re wrong here.ninjabeater said:A 90 degree twin has perfect balance of the pistons because they are moving opposite of eachother. They do not need a counterweight on the crankshaft.
Andy I'm glad you liked this question This subject can easily last for ages you know...Andy said:Aris,
Your question "why are 90 degree twins perfectly balanced" is a good one.
However, on a 90 degree twin, the second piston balances the counter weight even when it is at a 90 degree angle to the first piston.
Hi Aris,ariszr7 said:
The 6 inline on the other hand, is free of 1st AND 2nd order harmonic vibrations!