Need to rebalance rotating assembly?

[JTGS850GL]

I've noticed that almost no one had the rotating assembly rebalanced after replacing pistons with overbore pistons. Is this normal? Do people notice any increase in vibration after the rebuild? A little surprised about this since it was normal on cars to do the rebalancing and I figured it would even more critical since these engines pull more RPMs.

[blowerbike]

balance the pistons and be happy.
if the crank was a part you could balance the rods...that's as much as you can do on a press pin engine.

[JTGS850GL]

Really? Then there's no way to add/remove weight from the crank based on the static weight of the pistons? I would have thought there would be a way to compensate for more rotating mass. I guess I was wrong.

[Steve]

Oh, there is probably a way, but the only way to balance a crank properly is to SPIN it.

Since the rods are one-piece affairs, they will be spinning along with the crank.

Yeah, you could take the crank apart to take the rods off, then put the crank back together to balance it, then take it apart again to put the rods back on, then HOPE it's still balanced.

There is enough weight in the crank that the slight extra weight of the pistons will not matter all that much.

.

[JTGS850GL]

So, has anyone noticed any significant increase in engine vibration after installing a big bore kit on their engine?

[sparki]

no - but you can weigh each piston if you like and check they're all the same...

[stetracer]

I am a firm believer in making all the pistons weigh the same. Weigh the pistons on a triple beam scale leave the lightest one alone and make the other three weigh the same. I put the rings and wrist pin with the cir clips on the scale with the pistons when I weigh them.

[JTGS850GL]

Where and how do you relieve the pistons to reduce the weight to match the lightest one?

[rapidray]

I take weight from the underside of the pistons when I am balancing. If the weights are WAY off, I have even taken weight out of the pins if needed.
Ray.