crankshaft balancing

[Bain]

Is it absolutely neccesary to weigh the pistons and connecting rods seperately? If so why is that when they are going to be connected anyway while rotating? Reason I ask is I have been searching for a shop in the area to balance my new crank but had no luck so finally I decided to go have my pistons pressed on to the rods since I new someone who could do that. Then maybe twenty minutes after getting home with them I found a garage that could balance the crank and everything and the guy tells me he has to weigh each peice seperately and he isn't sure if he can press the pistons back off without damaging them so I was wandering if that is how it's always done or if it's just this guys way of doing it? Thanks

[zagrot]

the reason that the piston assembly and connecting rods are weighed seperately is because the pistons, wrist pins, rings, and the small end of the connecting rods are purely recriproating mass whereas the crank journals and the large end of the connecting rods and the bearings are rotating mass. during crankshaft ballancing each end of the connecting rod must be weighed seperately. you might want to check with a machine shop to have the wrist pins pressed out.