Ok so here is the question.

I have 96 out back automatic wag., with a high rpm vibration. Vibrates in neutral and worse under load,say between 2500 and 4500 rev... It is definitely rev related. Not speed or drivetrain related. I coasted in neutral and is goes away. Unless torque converter,flex plate,etc. we did have a few flex plate bolts a little loose. and they are miss matched heads on the bolts. But could that be enough of a weight issue to cause this. seems unlikely to me.

 

Next issue. Had a new mechanic perform timing belt (campaign) etc, work done on front of motor. I am not sure if it had vibration prior to work done. I do know that i had him tear it down to inspect myself. He had crank on wrong mark, 3 teeth off. yeah the round mark on face of pully not the line mark on crank sensor pick up tooth. so at this point hoping valves aren't bent! At this point unsupervised by me again, he starts it up with the drivers intake 180deg out. . i get it timed up, but i don't know if he rotated one of the other cams too much during install, not to mention the other times it was out of time. Motor sounds fairly normal, no excess piston slap. No knocking. Fairly normal valve train noises. But that vibration is bad. Exhaust notes are normal , no miss fires. I have not checked compression but it cranks even though. Could bent valves make it vibrate like that? by the way it has 170k on it. yeah and no burned exhaust valves, one of the lucky ones. or unlucky.

Help

No, but a loose crank pully would. Or if he used a prybar to get the pully off and tore the bonded rubber inside of it. look at it and see if you can see it wobbling.

My experience with bent valves are no starts the motor cranks faster than normal because of no compression. Check the crank pulley like 91loyal said.

bent or damaged flexplate could cause the rpm vibration/noise......usually worse as RPM's increase......

i checked harmonic balancer, it seems straight. The rubber fill is all intact. Maybe I can double check the flex plate. thanks for the responses.

Actually, the mismatched bolts could very well be the issue. It doesn't take but an ounce or so to throw off the balace of the torque converter. You have a large diameter travelling at high speed and a small weight difference is vastly increased the further you get from the center. These items are designed for balance and the OEM bolts are matched for a reason

 

Make sure you match all of the flex plate bolts and I bet the problem goes away.