Engine vibrations…..

[HotRodder Glenn]

I have a 460 and a C6 in my 70 F100. I bought it this way so I know little about it. What I do know is the motor has been rebuilt at some point, and the previous owner said he had the C6 rebuilt in the spring.

At idle I barely feel it, but as you go up in RPM (just above 1000) the vibration gets pretty severe. This all running but in park sitting still. Once the RPM's get up high enough (over 3500) the vibrations seem to lesson. While driving I also feel it, but again, if you get above say 3k rpm it seems to smooth out. Maybe not completely, but not anywhere as noticeable.

Any suggestions? Things I can look at easily to try and eliminate the cause? I have read harmonic balancer, flex plate and also maybe a bad plug or wire. The truck does have plenty of power for what it's worth.

Thanks for any help,

Glenn

[tnlprt]

You might need to drop the oil pan and get the numbers off of the crank to see which balance it has

Does the Flywheel have a counter weight welded on it