First the background of the engine....

I bought it from a member on here at the beginning of '09 as a complete motor. Its a pre-86 block w/2 piece rear main seal, 2 bolt mains, and was bored 40 over. Crank is an Eagle 3.75" stroke, rods are Eagle 6" H beams, pistons were KB hypers (more on that), it had a Romac billet balancer and flexplate. Everything was balanced when the motor was first built.

When I got the engine, I pulled the heads off and found 2 cracked pistons and some knicks in the cylinder walls from those pistons. I tore the motor down completely, and had the block bored 60 over to remove the knicks. I rebuilt it with all new bearings, used the same crank and rods, but upgraded to SRP forged flat top pistons. Still have the romac billet balancer, but bolted up a neutral balance flywheel for my t-56.

Finally installed the motor last month, but it has a vibration. Of course it gets worth with increased RPMs. My question is, since it was balanced before the new pistons and flywheel, would they cause it to vibrate? Or is it just something that comes with a stroker?

I figure since the pistons aren't part of the reciprocating weight of the rotating assembly, it shouldn't have much affect, and since my flywheel is neutral balance, it shouldn't either.

Out of curiosity the other day, I pulled the Romac balancer and bolted up a stock harmonic dampener to see what would happen......it made the vibration 10Xs worse.

 

the flywheel and damper should be externally balanced. the weight of the pistons and rods affect balance.