[millemille]

If the issue of balancing a v60 Rotax engine after changing piston and/or rod weight was easy it would have been done many times succesfully - do you know how many times it has done, other than by the aprilia factory, succesfully? (quantify succesfully - retaining same levels of viabration and reliability as oem)Simple answer - never. Only aprilia/rotax know the pbf needed for calculations to remove weight from the crank and/or the balancer shafts. No one, other than aprilia/rotax, actually knows definitively what the two balancer shafts in the V60 engine actually do in relation to the dynamic forces of the reciprocating components of the crank assembly- the primary balance shaft every one is pretty much agreed balances primary forces generated by the crank components - though whether material needs removing from this or the crank to reatin oem primary balance after fitment of lighter compoentns is unknown, and as for the secondary balance shaft in the rear cylinder... does this balance the rear cylinder assembly, come into efect at higher rpm to balance the crank components or is it even there to balance forces created by the primary balancer? This subject is a great debate on numerous threads on Aprilia websites - people such as jet turbine engineers, formula 1 engine tuners, mechanical engineers (such as myself) and intuitively clever back yard tinkerers are all coming at this from different angles ('scuse the pun) with no solid conclusions or solutions.

Balancers only work for certain rpms and multiples thereof because the dynamic forces generated by the crank components vary with rpm - the higher the rpm the greater the force, don't even begin to factor harmonics. The mass of the balancer shafts is fixed therefore the effect of the balancer shaft is fixed. If you were building a racing only engine you would have the balancer shaft mass set to nullify the crank forces at a higher rpm than a road engine.