Loose crank pulley

A spot to watch on these, probably already mentioned on this site in the past, but I'm new here.....

I was doing an oil change on my S/C XR-7. I had noticed a knocking sound at idle a few days prior to this.
My mechanic looked at it and suggested that I remove the accesory belt and wobble pulleys to check for bad bearings.
I found nothing. I started the car without the accesory belt and it was worse!
Fearing the worst (broken crank) I removed the other two belts.
It was then that I discovered I could wobble the crank pulley on the balancer!
I reached into the crank pulley to feel for missing bolts and they were there, but the were broken and I pulled them out by hand!
The pulley was hanging there by a couple of threads!
I had to remove the balancer, drill into each of the four bolts, and using a Snap-On thread extractor set, I carefully got them out. It was tough getting grade 8 steel bolts out of an aluminum balancer but I did it.
I had to go to a machine shop and get grade 8 allen head cap screws to replace the rotten bolts. I reassembled it with lock washers and red Loctite. I haven't had aby trouble with it since. I have had it apart once after that, so the red Loctite isn't too tough for this application.

I was very close to a major meltdown!

Unfortunately a somewhat common occurence on the 3.8 SC motor. You were lucky in a way to catch it when you did, many people have them come right off ! Had to relpace the damper on my 95 about 14 months ago for a wobble, it hadn't started making noises or busting bolts yet. We had the engine running checking something else, and one of the techs here at the shop pointed it out .... D'OH !!


cheers
Ed Nicholson
SCCoO

So what are some of the other symptoms, besides "wobble", of a failing HB or crank? Can a HB be shot, but still show no discernable wobble?

The only other symptom that I can think of is a strike/rub damaged crank sensor. But if the HB moves enough to strike or rub the crank sensor then the crank bolt is probably broken.

so to sum it up:
wobble in the main pulley
broken or missing crank bolt
strike damage to the crank sensor

Aaron

Thanks

Crank Pulley

i had the same thing happen to mine but 3 of the 4 heads of the bolts that held it on were sheared off. i couldnt belive the belt didnt shred. but it was really easy to fix. just went to the local auto parts store and got the same type of bolts and replaced them.