[694X4]

OK this has stumped. i put a 406 small block in my truck and it had a vibration. well the thrust was out of it so i pulled i got a deal on a 383 short block fully balanced rotating assembly. every thing new. so i put my top end on this block eldy heads and manifold holly truck avenger 670. the heads only got around 5k the carb not sure bought it used. put new com roller cam,lifters and rocker on. it seems to run perfect but still has the same vibration. been thinking it might be the motor mounts they are round Polly bushings like in the end of a leaf spring. would you feel more Thur these types of bushings? has to be that or some thing that came off the other engine. the ignition was new with the heads msd pro billet dis,6a, blaster2, 8.5 wires. i all ready unbolted the torque con and eliminated that. it feels most strong at around 2500 rpm. any advice on this would be greatly appreciated

[S10 Racer]

Are you sure you have the correct harmonic balancer & flywheel on it? The harmonic balancer may have slipped. I had this happen on a 93 GT Mustang once and it shook terrible until I replaced the harmonic balancer. The outer ring had spun around the inner hub and put it out of balance. Check that first.

[694X4]

the balancer was balanced with the crank shaft and if it spun the timing mark would be off and is all good

[DoubleVision]

Was the crank externally balanced or internally? Is it a one or two piece rear main seal?

[694X4]

it is a one piece rear main and it is externally balanced.the rotating assembly came from a place out of Spokane computer balanced to .02 grams