1992 LT1 Wobble problem

Reply Subscribe

Thread Tools

Search this Thread

Dec 22, 2019 | 07:11 AM

Dan Reed

Thread Starter

Cruising

Joined: Feb 2019

Posts: 11

Likes: 6

1992 LT1 Wobble problem

I know there have been quite a few wobble threads (and I think I’ve read them at least twice), but I still have a couple of questions. I recently had my 92 LT1 rebuilt by a reputable shop and they replaced the crank in the process. After putting around three hundred miles on it, it started a pretty bad belt chirp. I could see the crank pulley wobble, removed it, and decided the rubber was in bad enough shape to replace it. I checked the torque on the crank hub bolt (70 ft/lbs by the FSM), and installed a new pulley. I started the engine without the serpentine belt and the new pulley still wobbled. Exchanged the new pulley for another one, installed the second new pulley, and had the same wobble. Re-verified the torque on the crank hub bolt, and it was good. I made sure that the cast arrow on the hub was at the 12 o’clock position with the number one piston at TDC and matched the arrow on the new pulley to that one. As far as I can tell, the crank hub looks like it’s seated on the crank snout. Is there a way to check the hub, or should I be worried about the rebuild/new crank?

Dec 22, 2019 | 09:39 AM

C409

Le Mans Master

Joined: Feb 2005

Posts: 6,479

Likes: 565

From: Clearwater Florida

..... The only diagnostic that I see here would be to remove the pulley and hub and possibly the timing cover and put a dial indicator on the crank snout and actually measure it for run-out … if so , then you got a bum crank …..

Dec 22, 2019 | 12:01 PM

Kevova

Le Mans Master

Joined: Sep 2013

Posts: 6,192

Likes: 750

From: near the thumb in the mitten

Sometimes the ears on the hub can be damaged by "a man and a big hammer" trying to knock it loose without a puller. Additionally to C409's check hub run out. A magnetic base dial indicator kit required.

Dec 22, 2019 | 12:39 PM

dizwiz24

Race Director

Joined: Sep 2001

Posts: 14,674

Likes: 751

From: NEwhere Ohio

Yeah i agree with the others.

dont ‘throw the baby out with the bath water just yet’ and say you got a bad crank.

im trying to remember, is there a bolt on fork at the end of the balancer (holding the balancer)that could be bolted on lopsided ? And is an easy fix ?

is it possible there is just a clearance issue between the hub and crank ? Isnt it press fit?
Are you tapping the hub on 360 degrees around and not just going gorilla on one side of it (which could get it started lop sided?)

I know this isnt your issue, but I would ‘key’ the balancer to the crank. There was an unused woodruff keyway in the sbc crank that i put a key in to my ati superdamper (its driving a supercharger which is why i was worried about harmonic balancer slip).

Last edited by dizwiz24; Dec 22, 2019 at 12:40 PM.

Dec 22, 2019 | 01:26 PM

C409

Le Mans Master

Joined: Feb 2005

Posts: 6,479

Likes: 565

From: Clearwater Florida

..... FYI … You should never tap a hub or harmonic balancer onto the crank snout … buy an installation tool or use a succession of long to shorter 7/16" fine thread Grade 8 bolts and a thick balancer washer to push it on …..

Last edited by C409; Dec 22, 2019 at 01:27 PM.

Dec 22, 2019 | 05:31 PM

Dan Reed

Thread Starter

Cruising

Joined: Feb 2019

Posts: 11

Likes: 6

Thanks for the quick responses! The balancer isn't press fit on this model, just bolted on with three bolts and torqued to 60 ft/lbs. Comes on and off pretty easily (once you figure it out, that is). There is a cast arrow on both the hub and balancer aligned with TDC of the #1 piston. I think I'll try to rotate the balancer 90 degrees, even though its supposed to be neutral balanced, just to see if it makes a difference. If that has no effect, then I'll probably pull the hub too and try to see if the "big hammer" thing happened, and try to find a dial indicator to check the crank snout. I have a puller, and while I most definitely appreciate the persuasive effect of the big hammer, I agree that this isn't the place to use it.

Thanks again, and I'll follow up when I know more.

Dec 23, 2019 | 08:12 PM

Dan Reed

Thread Starter

Cruising

Joined: Feb 2019

Posts: 11

Likes: 6

I took the balancer off and measured the distance from the frame rail to the hub ears and found that one was different enough from the other two to think about taking the hub off. So........ turns out you CAN remove the crank hub with the engine still in the car (at least on the 92 model). Is it fun? Nope. Not even close. But the only other thing I took out to get to it was the balancer, so you kind of get what you pay for, if you know what I mean. I'll measure the hub ears again, now that it's off and I can be a little more accurate, and probably wind up replacing it. I'll also check the runout on the crank snout and see what I can see (hopefully nothing out of the ordinary). Thanks again for the help, and I'll follow up with the outcome.

Dec 27, 2019 | 07:31 PM

Dan Reed

Thread Starter

Cruising

Joined: Feb 2019

Posts: 11

Likes: 6

Final update. I used an inspection camera to check out the crank snout and found my problem. I'm not sure who did it, or when, but whoever did it used the wrong key when replacing or re-installing the crank sprocket. From what I now understand, the 92-95 models LT1's use a deeper cutback cutaway key (that sits flush with the forward edge of the sprocket) and the 96 and 97's use a "normal" cutback key which sticks out from the sprocket, which the crank position sensor uses as an index. The back side of the hub had an indent in it from being forced onto the key. I'm assuming the hub wasn't sitting completely flush, which caused the wobble. I notched the back edge of the hub to accommodate the key, and reinstalled the hub. It goes on MUCH easier than it comes off, by the way. NO hammers required. Runs like a champ now.