engine balance

[Anonymous]

i had a stock rebuild done on my 68 200ci. it's going into a 66 mustang coupe. i pretty much have the whole engine together and a friend asked me if it was balanced. i checked with the place that rebuilt it and they said that the pistons and rods came as a matched set and that i would only have to rebalance the engine if i replaced the harmonic balancer. i assumed that by matched they meant all the pistons etc. weighed the same as each other, but i'm not sure if they weigh the same as the original parts? i've had some problems with this machine shop so i wanted to check with the group.

do need to take this engine apart and get it balanced? or is that only when performance upgrades are made and parts with none stock weights are used. i hope i don't need to balance it, that'll be a big step back. but in the end i want to do this right so...

by the way, the crank was ground down, the engine was over bored 40 mil.

thanks a lot in advance.

 

[CZLN6]

Howdy Evren:

It really depends on your intended use and your budget. If this is going to be a performance engine and see engine speeds in excess of 3,000 rpms regularly a complete static and dynamic engine balance is a good investment and cheap insurance. It this engine is going to be a low and slow commuter/cruiser, balancing may not be necessary.

Static balancing means weighing every reciprocating part and assuring that they are all the same. Rods should have both ends weighed seperately and equalized. This includes the pistons, rings, rods, bearings.

Dynamic balancing means every rotating part- from the damper to the flywheel. All parts are put on the crank, piston sets are dummied with bob weights, and the put into a lathe type fixture and spun at various speeds to determine balance, or lack of it. Weight is added to or subtracted from the
bob weights until balance is achieved.

Most shops don't have this type of equipment and it requires sending out. It costs in the $100 to $200 range for a six cylinder balance. It may cost that much for your shop to dissassemble, ship and reassemble the engine.

Choosing the right machine shop to work with is sooo important when building a performance engine.

Adios, David

 

[Lazy JW]

A stock rebuild needs no extra effort put in to balancing beyond stock specs. I have rebuilt quite a few stock engines to stock specs with no problems at all. Don't lose any sleep over this one. High performance/high speeds is another story.
Joe

 

[Anonymous]

thanks for the advice. i feel much better about it leaving it unbalanced now.