i was wondering if anyone has any advice about balancing a 3.75 scat cast stroker crank it is setup from scat for external ballance but i talked to a machine shop guy and he said that if i don't ballance the motor it will have enormous vibrations i am wondering what to do for it i have arp reconditioned rods a set of kieth black hyp pistons THANKS

 

take it to a shop and have them balance it, otherwise the motor will vibrate itself apart. Im pretty sure you might need some special equipment for balancing.

 

Geez id kill for a stroker eng for my 88,
intrnal balance like mentioned,worth it

 

Internal/external balance isn't the same as having the rotating assembly balanced. All internal or external balanced cranks mean is where the mass of the weight is located. Externally balanced cranks don't have the extra mass in the counterweights so it's added in the balancer and flexplate/flywheel.

The crank counterweights are at an estimate weight. To properly balance the weights, the machine shop needs balancer and flexplate/flywheel (if externally balanced), con rods with bolts, pistons, rings and rod bearings. All these are weighed and the crank's counterweights are balanced to compensate for the weight of the rotating assembly. All the rods are adjusted to the same weight and so are the pistons. Knowing where to remove excess weight is part of balancing.

Because of different piston and rod weights, a crankshaft is never properly balanced. Unless you're building a stock engine with stock components, an engine should always be balanced.

When I had my 540 balanced, I got an internally balanced crank. All 454+ cranks are normally externally balanced. Because of the lightweight rods and pistons in my engine, the machine shop had to fill one of the factory balance holes in the crank.

If a rotating assembly isn't balanced, an imbalance can hammer out the crank bearings especially at high rpm. The weight of the rods, pistons etc need to balance out the counterweights on the crank.

 

why do they seel it as a externaly ballanced crank then do they intend for people not to have to ballance it

 

They don't. An externally balanced crank will have less mass on the counterweights, in the expectation that it wil be use with a weighted flywheel and balancer. If you add weight to it, it can be internally balanced as well. The same goes for a crank sold as internally balanced, it will have more mass on the counterweights, but by removing that weight it can be externally balanced as well.

 

they don't what ?

 

oh ok

 

Either way, a new crank will need to be balanced.

 

well thanks for the info on this and for clearing it up