Engine Vibration - 3K RPM

[SSL]

I'm having a engine vibration at 3000 RPM and haven't been able to diagnose the problem. After about 300 miles of use, the vibration started and seems to be engine related.

Drivetrain Details:
- ZZ502, Fluidamper, Holley 850, MSD Digital6, March serpentine with AC
- T-56, Centerforce DF, Scattershield (indexed)
- Hydroboost brakes

Items looked at so far:
- Vibration occurs when:
- Moving and sitting still
- Clutch engaged or disengaged
- Trans in gear and out of gear

- Plugs and wires checked - plugs clean, gap correct
- Replaced waterpump

Any ideas on what to look at next?



Thanks,
Steve

[bbcc]

Internal or external balance? If its external check to see that 1) the dampener hasn't rotated on the shear pin 2) the weight is still fastened to the dampener 3) the weights are still fastened to the flywheel 4) there arn't any teeth missing or big gouges on the flywheel. If its internaly balanaced check for the same things, but if nothing is found you are going to have to drop the pan and inspect the bottom end. Also check the distributor and/or ignition box. Maybe swap these items with some known good ones.

Good luck bbcc

[jamieg285]

I had a similar problem with my 400sbc, although the vibration was at about 2K. I pulled the engine and put a different one in(no re-used parts) and the vibration is still there.

Being as it happens in or out of gear (auto), I now assume that it is the convertor or trans that is causing it.

[molyorange 77]

Is the Flywheel correct for that engine. I think those engines are externally balanced.

[Jim Nilsen]

Check your valve springs, if you have broken an inner spring it might do this. Just a thought that is a bit out there but it seems like you need to look everywhere you can that is easy first.

[SSL]

Finally figured out the problem...

Bent alternator shaft. Took the belts off and all is well. I'm relieved that it's not internal engine or trans related. Thanks for all who pitched in to help!

Steve