Engine Balancing

Does a motor have to be balanced with everything from the balancer to the flywheel to be correct? I mean, if for some reason you have to replace one or both ends @ some point, would you have to rebalance the whole rotating assembly including the rods/pistons/crank? How does that work? The reason I ask, my bother just had a motor built for his El Camino. I know, I know it's not Ford, but he's my little brother and I'm trying to help him out. The engine shop finished the bottom end and told him he'd need a balancer, since the original is missing. They went ahead and finished the motor and just need to put a new balancer and pulleys on it. I thought I heard somewhere that you have to have everything in the rotating assembly balanced together, and slapping on a harmonic balancer after the fact will make the motor run like crap.

Scott Williams '66 High Country Special

If you are building an engine, you SHOULD have the pistons weight matched, the rods weight matched, and the entire rotating assembly (crank, flywheel, damper, rod, and piston) precision balanced.

If you don't supply the actual damper and flywheel you'll be using, the machine shop will balance the engine with a standard damper and flywheel. You MUST make sure that you install the same type (not brand) of damper and flywheel the machine shop used to balance the engine. If the engine is internally balanced, then a balancer and flywheel with NO counterweight MUST be used. If the engine is externally balanced you MUST use a damper and flywheel the has the same counterweight the machine shop used (in Ford land this is either 28oz or 50oz).

Balancing the rotating assembly without the actual damper and flywheel you'll be using is not as precise but it's a standard practice and will cause no problems. Having the entire rotating assembly precision balanced is desireable and will yield the finest balance and the smoothest reving engine. When the balance is right, it is stunning how refined a high horsepower 5.0 feels.

LJH

95GT (331 stroker, precision balanced)