The Stovebolt Site Forums The Shop Area Engine Shop Out of balance check

I have put in a new sbc, and at about 2000 rpm it starts to act out of balance. It is especially noticeable on a hard downshift. Anyway to try and determine the culprit, other than start replacing parts? I have to assume at this time that it is an external part issue. It is mated up to a 4 speed.
Thank you for your help and suggestions.

Hy SD66Burb, we need more information to make intelligent comments, Engine size and year, components used, for example clutch/flywheel, balancer?

I would look at the u joints on the driveshaft, and check the rearend pinion bearing.

Check the hanger bearing for the driveshaft if it has one.

Another thought, since you replaced the engine, did you put a pilot shaft bushing in the crankshaft?

I kept getting burnt on rebuilding the 283, so I put in a new GM 350,290hp crate motor. Gen I block, new Harmonic Balancer, Clutch Disk, Pressure Plate, Old Flywheel resurfaced. It's in a 60 vette. Rest of drive line is good. It starts to shimmy while setting still, also moving

The flywheel is believe is your problem. If your motor has the one piece rear main seal you need a flywheel to go with the external balanced motor.

No, this is still the 2 piece seal, internally balanced.

Any of those new parts could be defective or out of balance but my guess is a bad resurface job and/or lost balance weight off the flywheel. Since it does it while the car is sitting, that isolates it to something in the engine or clutch area.

Thanks guy's, just thought I might get lucky, and some one would say, just do "this". Time to start tearing things apart

Check the new front harmonic balancer FIRST.

How do you check a Harmonic Balancer? I indicated the face and OD, and it runs good.

....burb, if its true your in good shape but be sure to check it for any cracks. When it starts vibrating take it out of gear but keep the RPM's up and see if there is any difference and if so where it is the difference.
Put it on jack stands and try a few things. Could it possibly be a tire mounted incorrectly as in the tire bead is not seated properly?
Let us know what you find out. Curosity is killing me!!

AChipmunk, sorry for the delay, but I have been feverishly trying to sort this thing out. Good news is, it's gone, bad news, not sure what exactly it was. You know the old addage, if you throw enough time and money at it, it will eventually go away. I had the tranny out 3 times, and the last time I took the bell housing back off, rebalanced the flywheel and (new) pressure plate, changed pressure plate bolts, reflattened all faces of bellhousing, crank flange, etc. Vibration gone. Now I get to enjoy it.
Thanks everyone for your help.

congrats and thanks for giving everyone the heads up