Terrible vibration

[GRNOVA]

Hello all,

I started the 65 Nova and drove it again 2 weeks ago. I noticed a bad vibration when accerating, thought it was a driveline problem. But when I let off the gas ,at about 40 or so ,the vibration stops, get back in it an it starts all over till I let off the gas. I Had the trans checked nothing wrong. Also checked the flywheel notI have a mid plate and soild motor mounts. The engine is a small block chevy 383 eagle crank and rods J&E dished pistons w/ B&M 250 blower. I did a little research on the crank and it is suppose to be an internally balanced crank....But My flywheel and harmonic balancer both have big weights on them. I'm a little confused by this. What should my next move be I pulled the motor last week.

Thanks

[69LT1Nova]

I had this problem with another car. The car was originally a 400 sbc, but it was replaced with a 350. The previous owner was an idiot and re-used the balancer and flywheel from the 400 on the 350. Vibrated like all hell.

I put in a new balancer and flywheel for an INTERNALLY balanced motor, and it ran great... until 10K later. Turns out that the unbalanced rotating assembly wiped out the main bearings. Best of luck to you man, hopefully you aren't looking at a complete tear-down.

[GRNOVA]

I just got off the phone with the engine builder and he said he would run the rotating ass. on the balancer and do the work for free if there was a problem. Looks like a complete tear down is on the list of things to do tonight. He wants it Saturday morning and wants me to be there.

[Blown353]

Vibes under load only point to a drivetrain problem and I would check that before diving into the engine... I think you were a little premature pulling the engine before doing a bit more in-vehicle diagnosis.

How is the pinion angle? Did a shim slip out from between the leaf & rear end (assuming you still have the leafs) throwing the pinion angle out of whack? How are the u-joints? Any excessive play between the driveline slip yoke and the transmission tail shaft?

If it's an engine imbalance, it will vibrate under load or not so if you just free rev the motor out of gear with the car not moving it should vibrate too.

[GRNOVA]

Blown 353,
I checked the drive line when I had it at the trans shop the drive shaft still had all the weights on it. It was just made 2 months ago so I am assuming it was still balanced. The pinion angle was checked and seemed to be fine. The motor did tend to vibrate a little when revved up out of gear, to try and stablize this I installed a mid plate thinking that would correct the vibration. Nothing. I also ran the engine on the lift thinking the flywheel might be bent,again nothing. I tried to think of everything before I pulled it, but came up with nothing. So I pulled it.

[GRNOVA]

Just Brought the Engine back from the Dyno Shop. Has anyone heard of rotor phasing? Where the two purple wires on an MSD ignition should not line up, well mine did, that is the way it came out of the box. That was the problem that caused the "Vibration" Not to mention the fact that the end of the crankshaft was missing the locating pin for the Flywheel. This caused the weights from the balancer and the flywheel to be misaligned. What a day though putting the engine on the dyno was awsome I also have some video I will post later.

[TnBlkC230WZ]

I have to ask, did you put the pilot bushing in if you are running a manual?

[6'9"Witha69]

Not to mention the fact that the end of the crankshaft was missing the locating pin for the Flywheel. This caused the weights from the balancer and the flywheel to be misaligned.

Been there on my first 383 build. A mistake I have never made again.

[Doug G]

On my 406 years ago I had a similar issue. By chance I heard a pop out the exhaust every so often. I put my hand over the exhaust (duals) it would suck back every so often on one side. I pulled the valve cover and found a broken valve spring.

[GRNOVA]

opps