Memorial Day mystery noise

Here's one that is baffling me. A couple of days ago I was in stop and go traffic and I kept hearing what sounding like a VERY noisy AC compressor, but I thought it was a car around me as my AC compressor is new. Well, traffic finally opened up and I no longer heard the noise, so again, I wrote it off as someone else's problem. Then I arrived at home, came to a stop, put it in Park and damn if the knocking did not start up again. I killed the AC so as to eliminate the compressor as the culprit. Still there. I got out and checked for anything obvious, nothing found. I tried using the old long handled screwdriver to the ear and around various areas on the engine and the various engine driven accessories, but could NOT isolate it. I found that if I idled the engine up to between 900 and 1000 RPMs the knock totally vanishes. To further isolate the problem, I pulled the serpentine belt complete off all the pulleys and balancer and then started the car, NO KNOCK. I put in drive to give it a bit of a load NO KNOCK, I tried various idle speeds, NO KNOCK. As it seemed to be something in the engine driven accessories, I started with the most likely, the tensioner pulley but that did NOT fix it. I replaced the power steering pump (factory original) but again, that did not fix it. I then replaced the entire tensioner assembly thinking that maybe it was not holding sufficient tension under load, but again, NO fix. I also installed a new serpentine belt just to ensure that it had not stretched, but again, NO fix.

When I spin the alternator it spins freely and without any hint of an issue. I can likewise do the same with the water pump. That leaves the harmonic balancer as the only culprit that MIGHT be at fault. I did tug around on the balance and it seems solid, but I know that it could still be a fault.

Again, I can pull the serpentine belt and the engine purrs like a kitten at idle or under load. Put the belt back on and at low idle it sounds like it is about to come apart.

I don't know that I want to tackle the harmonic balancer as a DIY project, but at this point, I am running out of things to throw money at. Any thoughts as to what might be causing the knock/rattle noise? (FYI, it is NOT the same sound as a rod as the frequency is wrong and it is irregular to some extent and again, without the serpentine belt the engine purrs perfectly regardless of load or rpm.

Any thought will really be appreciated

Fingers are pointing towards the harmonic balancer. The reason why the noise goes away without the belt is because the load is off it.

It's your HB. Kinda sounds like a bag of nickles in a washing machine at Idle. The only hard part is cracking the nut loose. ROJ has the procedure for using a breaker bar and the starter motor. Never worked for me but it is the simplest method. An impact gun probably won't do it either but worth a try if you have one. Go to method is add a 4 or 5 foot pipe onto the breaker bar and go for it while using a gear stop or vise grips on the flywheel to keep engine from turning.

Don't forget to change the CPS while you're in there or you'll be getting a repeat performance sooner than later. Be sure to check the clearances between the chopper rings and the CPS and tighten down too.

David,

I recognize you as a somewhat regular on this forum, I am absolutely amazed you were not aware of the near 100% failure rate of the dampers on the 3800 and the symptom of a knock at idle. Also surprised you did not post before all the work.

Remove your belt, grab the pulley on the damper and rotate it back and forth to verify your failure. It should clunk when it hits the internal stop, I have even been able to grab the belt with both hands and achieve the same results without removing belt.

Replacing the damper should be well within the DIY range if you have a good impact wrench to remove the bolt which is torqued at over 200 ft lb. I will admit that getting the damper to slide off is difficult without a special puller. I have been able to tap it with a brass drift at rear bottom of pulley and slowly work it off the crank. DO NOT SHOVE SCREWDRIVERS AND PRY BARS BEHIND PULLEY AND TRY TO PRY IT OFF!!!!!

OK, I was really leaning toward the HB as the culprit but at the same time I had ruled it out due to the fact that it was NO play in it in ANY plane of motion. Then a friend that had been out town, (retired master GM mechanic) dropped by and I let him take a look. He went thru the same process as I had done, but he was able to find the knocking noise was a bit more pronounced on ONE of the water pump bolts (long screwdriver to the ear test). He then removed the belt and turned it by hand and pronounced that it was failing due to the tension he felt on it. So back to the FLAPS for a water pump. Fifteen minutes to R&R the pump and BINGO, knocking gone. In all my years I have NEVER heard a water pump make so much racket and have NO leaks, and NO play on the shaft. I have heard motors with loose rods that made way less knocking that what I was hearing. As for replacing the other items, they were all factory original, so I just put chalk up such things as ongoing restoration as sooner or later I was going to have to replace them anyway. My buddy also looked at the HB and stated that it was the design that gave the least issue.

Thanks for all the feedback.

Well, that's a first. Never heard of a water pump failing like that before either.

Sure beats R&Ring a HB!

Well, there goes my armchair Internet diagnostic credentials

Well' date=' there goes my armchair Internet diagnostic credentials[/quote']

Mine too!!! I looked but didn't find an icon that represented "A blank stare with mouth agape"!!

All,

I too thought that the HB was the issue here.

Kinda sounds like a bag of nickles in a washing machine at Idle

I have tried to come up with words to describe the sound the HB makes when failing. This one is pretty good.

My thought was that it makes the sound of dice rattling around in the leather cup used in the game of Cribbage.

You say that there is no leather cup used. Well... there is (was) one used at Vic & Jim's tap in Loves Park, IL.

John F.

I think I may go ahead and tackle the HB in the near future as the car does have 132K miles and the balancer is original. I would rather tackle such projects on my schedule and given that these HB have such a bad history, it is only a matter of time...and as pointed out, I will replace the crankshaft sensor as well as it has been on the car for about 20 years (failed while still under extended warranty).

i would think replacing the "crankshaft balancer" (as the manual calls it) and the crank sensor is a good idea (if you have the time, etc.) - it's going to go out anyway at some point!

if you can see any crack in the rubber - front or back - that's enough to do it. mine had small chunks of rubber missing...

it's not fun to do, but between the ROJ tutorial and the FSM, it was doable for me...

My thought was that it makes the sound of dice rattling around in the leather cup used in the game of Cribbage.

I respectfully submit you must mean Backgammon, Cribbage is played with cards.

I'm experiencing this very noise. Guess I need to order a water pump. Thanks for posting.

Here it is days later and I've replaced both tensioner pulley and water pump no success so far. I'm thinking Harmonic balancer next, but it is in very good condition.

Here's what this sounds like: http://youtu.be/zByIHguMdmY