93redlt1

My friend is getting a bad vibration from his car. He has a similar setup as me but his car has forged pistons. Now the balancer shop added wieght to his crank to balance the setup. We made sure the headers are not hitting and the vibration occurs in park. The motor mounts are new stock gm pieces. Does the flywheel need to be zero balanced since this setup was had weight added to the crank. Thats the only thing i could think it could be. Any help is greatly appreciated.

Mean Green

the shop should have balanced the flywheel with the crank also. if they didn't that's most likely his problem.

93redlt1

yeah the flywheel still has the stock weights on it but i know his crank has added metal to it. so thats what i think it is. i think the wiehgts need to be knocked off the flywheel and it zero balanced.

med_reject

the shop may have added weight to the crank to balance the rotating assembly without taking the flywheel into consideration. If that is the case, then yes, the flywheel needs to be zero balanced.

SS RRR

You need to call the shop and find out if (what has already been stated) the rotating assy. was internally balanced. If it is then yes you need a zero balanced flywheel and the car should not be started again until it's installed...

SStrokerAce

BINGO! That's your problem....

Please fix this now before you keep driving on this and destroy the bearings in the motor.

Bret

MachinistOne

And you might want to point out to that shop that one piece rear main chevys are internal on the front and external on the rear.

12SCNDZ

Let me see if I understand this... I had my rotating assembly balanced for my 355 also. The shop had to add weight to the crank to balance it. It's a factory LT1 crank, Lunati 6" H-Beams, and Ross nitrous pistons with an LT1 Fluidampr. Should I also take my flexplate (auto car) to them to have it "zeroed"?

Frank

MachinistOne

Basically when chevy switched to a one-piece rear main seal, the got rid of the off-set flange on the back of the crank which made the engine internally balanced. Now the weight is added onto the flexplate. So on the front half of the motor the damper is neutral balance and the rear half the flexplate is weighted. This means that motors before '86 could be balance without the tech having the damper or the flexplate because they were "zero" and did not effect the balance. But with one-piece rear motors, the flexplate should be bolted to the end of the crank during the balance because it has off-set weight that effects the rotating assy.

So yes, the shop should have your flexplate in order to balance everything as best possible, I would assume that they have their own late model flexplate that they use for balance jobs, otherwise they would ask for you to supply it. IF they added weight to the rear to compensate for lack of weight on their flexplate, then yes, you need to have your late model flexplate balanced to "zero" like you said.(Cut the weight off and check zero)

On street motors the balance is not as close tolerance as race motors, for which we actually balance everything, damper, crank,flywheel, pressure plate, clutch disc , etc.

BTW Frank: My core tranny should arrive at your shop this week, it has C/O Cutler written on it.

93redlt1

ok guys i think i figured it out. i disconnected the flywheel from the torque converter started it up and vibration is gone so i think the converter is messed up. Can i use the stock converter on his car for now.