Posted By: bonefish
balance ? - 05/07/12 02:19 PM
im going to lower comp.from 12.5 to around 10.5.can i9 just re balance the pistons?
balance ?
Posted By: MR_P_BODY
Re: balance ? - 05/07/12 02:43 PM
No... your changing the reciprocating weight so it
would MOST LIKELY end up with a different bob weight
and need to change the crank weight.... but it depends
on how much weight your talking about with the pistons...
JMO... I'm no pro
would MOST LIKELY end up with a different bob weight
and need to change the crank weight.... but it depends
on how much weight your talking about with the pistons...
JMO... I'm no pro
Posted By: CompWedgeEngines
Re: balance ? - 05/07/12 03:26 PM
Unless you KNOW the weights of the 12.5 pistons, AND can match that weight with your new pistons ( I doubt it), you'll need to rebalance. It is possibloe at time sot get pistons close, and swap wrsit pins for tool steel, and hence take out wieght of the piston assembly, but unless you know all the weights, hard to say.
Balancing is not an option on a race engine, you simply need to do it right.
Balancing is not an option on a race engine, you simply need to do it right.
Posted By: bonefish
Re: balance ? - 05/07/12 03:28 PM
i was just thinking if you balanced the pistons in relationship with on another it would be the same end result,like take the lightest piston then the second lightest and duplicate the percentage of the differance.
Posted By: MR_P_BODY
Re: balance ? - 05/07/12 04:15 PM
Quote:
i was just thinking if you balanced the pistons in relationship with on another it would be the same end result,like take the lightest piston then the second lightest and duplicate the percentage of the differance.
They/you balance the pistons to one another on any
balance job but if the weights of the pistons are greater
or lesser than the ones you have been running then
the crank needs to be changed in weight
Posted By: B G Racing
Re: balance ? - 05/07/12 04:16 PM
The piston must match the weight of the ones your replacing,don't forget to include the rings,locks and wrist pins with the total piston weight.If the new piston is a touch lighter,-1 gram you should be fine. 
Posted By: smokinwoody
Re: balance ? - 05/07/12 04:23 PM
my engine is in the shop now being rebuilt as a pump gasser...had to dish the pistons to lower the compression...the whole rotating/piston assembly is re-balanced...
Posted By: Locomotion
Re: balance ? - 05/07/12 04:50 PM
Quote:
i was just thinking if you balanced the pistons in relationship with on another it would be the same end result,like take the lightest piston then the second lightest and duplicate the percentage of the differance.
To help put it into perspective, the "counter-weights" on the crank shaft are just that - weights to "counter" the weights of the rods and pistons while everything rotates. A balance machine as well as gram weight scales are required to do it right and minimize vibrations.