First time engine start, run and vibration.

[71LS5Formula]

Hey y'all. I finally got the car going. Once I get things sorted out I'll update my car on here. It's a 71 455. Stock bottom end. It is internally balanced. Summit racing steel flywheel. Here's what's going on. I start the motor and it idles liked it should. As I bring up the rpms a vibration appears. It's a quick vibration. It does not take that many rpms to get it to do it. When I shift gears and the rpms comes up cause the fitech is still learning I can feel it. I'm leaning towards the harmonic balancer, but I would liked some advice before I pull things apart. Thanks in advance.

Ben

[gator68428]

Make sure its not something simple like a plug wire being disconnected. And make sure you got a neutral balance flywheel since bottom end is internally balanced. Not sure how harmonic balancer would cause a vib... unless the rubber is loose or something

[71LS5Formula]

Flywheel is for an internally balanced motor.

[andrewb70]

Does the vibration appear if you simply raise the RPM while not moving?

Andrew

[71LS5Formula]

Yes.

[oleyeller]

Check the flywheel for runout and wobble. I had one that did not seat on the crank, I should have noticed, cause the transmission was difficult to stab, but it shook like a beast.

[71LS5Formula]

This one isn't shaking that bad.

[TheJDMan]

Back to the harmonic balancer, is it old or new? Stock or aftermarket?

[71LS5Formula]

Looking to be the flywheel. Was sold the wrong one.