Going from a flywheel to a flexplate

If you have a balanced motor can you change the flywheel to a flexplate? Wouldnt this cause it to be overbalanced. Would you have to rebalance it?
396

Balance has nothing to do with what the total weight is on the back or front of the crank. It is where the weight is distributed in relation to counterweights, etc. If a motor is internally balanced, swap away! No problem, if the motor is externally balanced, problem. The problem is the manufacturers tolerances. We had a customer with a 454 in a dragster and due to his own stubbornness he ruined 7 flexplates, since we built the motor we rebalanced every one of them to the original offset weight. They were all SFI approved and of 3 different manufacturers. The weights were off by as much as 11 degrees and 24 grams at 6". It would have shaken with all but one of them. The manufacturers half-ass balance to somewhere near zero, and then just weld on the weight with a fixture for the externally balanced stuff, they don't check the offset weight after they are done. The same holds true for Chrysler torque convertors which have the offset weight on them. Any competant shop can balance the flywheel to the flexplate or the other way. All it takes is a computerized balancer. About 10% of the balancers in the area can do it. The others have old-type units. We charge about $20-25, depending on how long it takes. TIMINATOR

soooo....the bottom line here is...if u have an external balanced eng (new)...u need to have the flexplate balanced along with all the other parts when its put together...correct???
fastrat

soooo....the bottom line here is...if u have an external balanced eng (new)...u need to have the flexplate balanced along with all the other parts when its put together...correct???
fastrat
Yes, and the harmonic balancer. On the other hand, as stated above, even on an internally balanced engine, you might want to check the flexplate just to make sure that it is really a neutral balance. Many are just welded and assumed to be close enough. I have seen quite a few out of the box that weren't even particularly flat. Had one that was so bad that it nicked the starter housing.

You should balance all engines, the factory kinda balances their engines but they do it as an assembly, after it is in shortblock form. If you dissemble a factory motor you need to put the same piston/rod combo back in the same cylinder or a shake is probable. The Olds motor in the upcoming article had rod weights off as much as 22 grams. We balance every motor we build. Only after balancing everything and then spinning up the crank with the bobweights on it, can you tell if it would have shaken from imbalance. We have had 2 in the past 10 years or so that would have been OK. Since we have done about 500 motors+ in that time, the odds aren't too good. A local high volume builder lowered their balance warrenty claims by matching the total rod weights, that lowered claims to I believe they said 6%. Any shaking engines were then balanced and resold. They said it was cheaper in the long run to do it that way. They are out of business. So are their other competitor that did things the same way. They both sold about 50 motors a day to the discount stores. TIMINATOR

. . .and any SFI flexplate with a cat stamped on the wheel as a logo stay away from.

I'll second that! Worst runout I've ever seen! TIMINATOR