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Originally Posted by millemille
Counterbalanced engines viabrate because they operate over a wide rpm range.
There will be an rpm, and multiples thereof, where viabrations do not exist. This is due to the primary balance factor used in the balance calculations - an engine can only be balanced for a set rpm, or multiples thereof (unless an engine, such as ducati 90 degree v twin, has perfect primary balance). Engine manufacturers decide during the R+D process where they believe the engine will spend the majority of time within the rpm range - the primary balance factor will then be derived to balance the engine at some point within the chosen band.
Anyone who believes otherwise is welcome to throw their hat into the ring on how to fit lighter pistons and conrods to a rotax V60 engine and retain primary balance via the two balancer shafts.....
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not to hijack a thread here but, what does RPM matter when the balancer is spinning at the same speed?
and why do you think they use the term
primary balance? Simpe, because there are secondary forces, and when you throw in a counterbalancer, it adds in its own secondary forces.....despite of what RPM youre at, no engine will ever be 100% vibration free.
Balancer isnt a good name, since they dont really balance anything, just get the vibes down to a tolerable level.
And putting lighter conrods/pistons in your aprilia should be easy, provided you know the math to figure out how much mass to reduce the counterbalancers by....reminds me of an old harley trick, guys would get an 883 sportster, bore out the cyls and put wiseco 1200 pistons in them, and it actually improved the balance because wiseco 1200 pistons are slightly lighter than stock HD 883 slugs.