Noisey '92 Bonneville - I'm getting worried

The idler pully is the most likely suspect. Pull the belt back off and spin the idler and check it for wobbling or side-play.

Hi Jack check the idler and tensioner pullys could be bad bearings or weak or broken tensioner spring.

Jim.J

"Jknomail" wrote

You may have a harmonic balancer that is coming apart.

Ian

Sorry. I left that off the list of stuff I already replaced. I replaced it, and the noise didn't change, so it's back in the box to be returned.

JK

Can you explain a little more? I've never heard of a harmonic balancer coming apart. Would that explain the lack of noise when the belt is off?

Still searching...

Jack

Mine came apart a month ago. It is an expensive piece (~ 420 dollars tax included plus labor about 80 dollars). You should hear a clunk noise when you start the engine and it will rattle at idling. Increase idling to about

1200 rpm or more, the noise should be less. You can verify this by using work light with a mirror to check for rubber crack along the puller and rubber. Or remove the belts and try to rotate the pulley both direction. If it turns, it's broken. Check the picture enclosed. If it is the harmonic (pulley) problem, limit your driving or driving as slow as soon as possible to prevent engine damage. As for water pump. You should hear a rolling (grinding noise) not rattle.

Cheers, Paul

One common problem is the Harmonic Balancer coming apart due to being oil soaked from the fron crank seal & therefore detoriating the rubber material of the Balancer causing a vibration.

Another possiblity could be your Belt Tensioner &/or Idler Pulley. I've seen both of these bearings make a noise when their live's have ended.

"Jknomail" wrote

Most harmonic balancers have an inner and outer section that are held together by a rubber section. When that rubber section breaks....you can get a lot of noise. It's not real common, but it was common enough on the 3800 to tell you that you may want to check that before you replace a bunch of other parts.

Ian

I think the rubber is deteriate due to life in service and heat. When I replaced mine about a month ago. There was no engine oil both outside and inside of the pulley.

mental note to self : Check Harmonic Balancer Pulley.

========= Harryface =========

1991 Pontiac Bonneville LE, 3800 V6 _~_~_~_~276,100 miles_~_~_ ~_~_

That's it! I took the belt off, and I was able to turn part of the balancer. It even made the same rattling sound when I turned it by hand. I'm picking up the part today, and I should be much quieter by this afternoon. Now, why would anyone make a harmonic balancer out of anything but solid steel? Making one half out of rubber just doesn't make sense to me.

Anyway, thanks to all of you. This NG rocks!

Jack

When I looked in my pontiac manual, it has a section for diagnosing engine noise in the valve train. It describes the noise exactly, and how the noise will diminish when the rpm's increase to 1500 or more. Then it says "The problem is not in the valve train. Replace the balancer." I just don't understand why any balancer would be made partly out of rubber, except maybe so they can sell you a $100 part later on.

Thanks again!

Ever stop to think that maybe it has to do with dampening vibrations so your engine doesnt shake apart? They have been doing them that way for for a very long long time.

"Jknomail" wrote

Because the balancer is designed to dampen vibrations from your engine. Most of them are designed this way. Some engine lines have almost no failures with harmonic balancers, the 3800 just happens to be one that does have the occasional failure. We all get old you know.

Ian

I know what the balancer is for. I've just never seen one made with rubber. I guess I've been out of the field for a while. The harmonic balancers I remember were always steel, and were made specifically for that engine as it was built. I guess I'm showing my age...

Jack

Right again, Ian - I mean about the age thing :)

The balancer wasn't too difficult to replace. The hardest part was turning the bolt on the puller, while crouching in the wheel-well. The rest was a breeze.

Thanks again for your help!

Jack Bass Wishes from South Florida Jack

Reply by email to k a z e e jk at ay-oh-well dot com. Just remove the spaces, fix the last part, and so on.

Here is a brief description from the internet.

Crankshafts vibrate with a twisting motion due the torque variation that results as each cylinder fires. This vibration is at its worst at some critical RPM. On a V8, this RPM is typically in the 4-5000 RPM range. If you operate the engine at this critical RPM without a harmonic balancer excessive vibration will eventually BREAK THE CRANKSHAFT. DON'T LEAVE IT OFF.

A harmonic balancer modifies the vibration characteristics of the crankshaft and flywheel assembly. They are made from of a heavy steel ring mounted over a thin layer of rubber on the outside of a center hub. The rubber acts as a spring. The ring twists on the rubber to cancel out crankshaft torsional vibration. Some energy is removed as heat in the rubber but the balancer's primary function is to store energy and return it to the crankshaft at just the right time to suppress vibration.

Paul

Thanks, Paul. I guess this "new" way of making harmonic balancers does make sense. You don't have to make one specifically for each engine as it's built, and the rubber's ability to store and release energy has to work better than a hunk of steel. By the way, my Bonnie is purring like a kitten with her new balancer. I think it must have been going for a while, but just started the loud clattering. Maybe it's in my head, but I swear the accelleration feels much smoother.

Jack