@paul-wannenburg Paul, An "out of Balance" situation with your current pistons would be unusual. One of them could have had a piece break off but this is unlikely. If the pistons were replaced and one of them was heavy or light, you could have this result. But again, this is not likely. 

You have not told us what engine you have so maybe that info would be helpful.

Mike

@paul-wannenburg

Hi Paul

As Mike said, we need to know what engine you are working on.

If you are working on an in-line six cylinder engine, they are said to be naturally balanced, which is kind of true, but really this in regard to "static" balancing.

Using aluminum in place of cast iron will definitely throw out "dynamic" balancing, but I doubt old Chev sixes were dynamically balanced, and doubt it makes as much difference on an in-line six anyway.

It should make more of a difference on all other engine configurations.

I do know for example that styled AR John Deere's were dynamically balanced, and early ones used cast iron pistons while later ones used aluminum.

Someone I know replaced the older cast iron with the newer aluminum and the difference was definitely noticeable.

Thanks for replies. Motor is a 216. i balanced flywheel,clutch and pressure plate. Opened ball joint behind gearbox to inspect universal. Trying to locate vibration at about 2000 rpm. Jacked up rear axle on stands and ran engine. Balanced rear tyres. Removed sump and saw it had aluminum pistons. All that is left now is to remove drive shaft. Thats a big job.

When I had the engine in my 38 rebuilt, I replaced the pistons with aluminum and noticed no difference in vibration. Is it possible the balancer got positioned wrong?

@paul-wannenburg Do you have the vibration when in gear and driving only or also when running the engine in neutral? If when driving and you shift to neutral does the vibration go away? Aluminum pistons in place of iron will not affect performance .

@steve-d Thanks Steve. there was vibration while coasting. I removed the crown wheel in the rear axle and removed the drive shaft. There was 2 indentations in the shaft near the pinion end. Looks like the marks were vice assisted. So a new shaft to be made up.Dont put that welded pipe shaft in a vice folks.

@paul-wannenburg The driveline shops I am familiar with can cut the old tube out and re-use the end yokes and then balance the shaft. I would ask them to check your shaft prior to having it repaired or replaced to verify that is the issue.