I read a ton of postings but couldnt find exactly what I am looking for.

I recently rebuilt my SC snout and replaced the coupler due to a loud clattering noise. And of course the noise is still there. I heard about this harmonic balancer problem and also eek.. saw something about a front main bearing problem in 94 bonnevilles...ouch.

So anyway I am hoping that its the HB.

Heres what we have doctors...
The patient exhibits loud clattering, knocking, etc... coming from the belt side of the engine although even with a stethescope I cant exactly locate... while running at idle and under slight acceleration.

With a new coupler and snout rebuild with only minutes of running time:

The noise is unoticebly different with only the outside (PS, alternator, HB) belt on.

The noise is essentially the same with only the inside (SC, WP, HB, AC) belt on.

With both belts off the noise is practically gone except for like an occasional banging, ringing noise coming from the HB area...I think.

So if its the HB, can I visually see the problem??? I really cant see anything wrong with it. It doesnt wobble and no noticeable scrapes or clean metal like its hitting something.

I really hope its not the Front Main Bearing, but how can I tell... easily?

Ok, thats my dilemma, hope to get this thing fixed ASAP, I am sick of sharing the mini van with my wife, and she cant drive my beater honda cus its a stick.

I see plenty of postings for how to do these jobs, however unpleasant, but I really need help diagnosing the problem. Any ideas appreciated.

GO BADGERS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!

Does the noise go away when the engine is under load (i.e. when you give it gas)? If so it is your Harmonic Balancer.
Also, is there any fluid around the water pump? If so it is possible that the WP is the problem, but very unlikely to make that much noise. plus the WP will howl.

Good luck and let us know what you find out.

With both belts off, try to move the HB around. It shouldn't move much if it'* in good condition. You should also see the rubber backing cracking and tearing if it'* bad. As the rubber wears, it clatters against the hard stop pins. I would expect the noise to be slightly different with neither belt biasing it. This does sound typical of a HB failure, so a visual inspection on the back side should confirm it. I just went through this with my boss on his 95 Rivier L67.

Hooray, I have it fixed!!!

It was the Harmonic Balancer but not what we thought. It wasn't the backing flaking off and hitting the stops, it was the rubber center. All around the edge of the pulley it was cracked and seperated. When the power from the belts was applied it would slip and bang. When the belts were off, it was just banging around. That middle bolt was a pain to get out though. Nothing a little heat couldnt fix however, oh yeh and an air impact wrench cranked to 160 psi.

Its running great now. Lots of rubber on the pavement and since the SC was just rebuilt, it just purrs...

I do have one question however, on the little vacumm thing for the SC that is on the front of the SC that runs the SC flipper throttle thing, there are at least three vacumm lines, on the right side, as you face the engine, the one closest to the front, I cant find any line to put back on it. I dont remember taking one off but it sure looks like it should have one on it. Any ideas where i could look to figure this out. It seems to run ok but maybe a little rough at idle.

Thats it, thanks for your help guys...
I am very happy.

The bottom port on the BCS (boost control solonoid) didn't have a vacuum line. See the funny clip retainer top and bottom? It held a foam filter for the vent. No worries. Mine deteriorated years ago and still runs fine without it.

Great work on the HB. Glad you got her running again!

Glad to hear you got it fixed. The HB is a fairly common problem on the Series I L67 -my parents have done theirs 3 times -twice on their old 1992 Park Avenue Ultra and once on their 1993 Park Ultra.

Happy motoring (and boosting).

I'm still on my original HB at 110k, but probably not for long.

I would say you might as well get one now because this HB was SHOT to H@#$%!! Ive never seen one screwed up like this one was. My car has 117000 so you know youre days are numbered.

Oh one more thing, I feel ashamed to admit this and its hard for me but I had no alternative, ok, understand...I got the HB from the stealership (i stole this and i love it) and I paid, well... um, like I had to right...$237.00. Did I really get cranked or was this in line. One dealer even tried to get 269.00. What have you heard of these obviously made out of gold HB'* going for?

oh yeh, thanks for the scoop on the BCS. I was looking everywhere for a studid vacuum line.

If you have the part # available go to www.gmpartsdirect.com and compare the list price to what you paid. Then compare the discounted price to what you paid.
Hope you don't find you been suckered too bad.
I forget what my parents paid, but my sisters old 1995 Buick Riviera (supercharged 3800) had jiffy Lube drop it from the lift (don't ask) and it put a 3 inch dent in the oil pan and ruined the HB. When she went and got the price for a new one at the local Buick dealer she decided to buy a good used one -the dealer wanted something like $280 + another $200 to install it.