Harmonic Balancer Wobble
There is a fair amount of discussion in that "other" corvette forum regarding harmonic crankshaft balancer problems in C6's with LS2 engines. The problem with 2005's is covered under TSB 05-06-01-001 and is due to a loosening crankshaft pulley bolt.
There are also reports of problems with 2006's where the rubber to metal bonding in the balancer is failing early causing it to wobble and damage the serpentine belt as well as components driven by the serpentine belt (idler, tensioner, alternator). The early warning is a constant chirping noise coming from the serpentine belt system.
Well, guess what. The belt on my 06 is chirping and the balancer is wobbling! It seems that some visible wobble is acceptable - although this makes no sense to me. A device which is designed to dampen harmonic vibrations should be true! Otherwise it would generate vibrations of it's own.
So, has anyone in this forum had experience with this issue? How much is too much wobble? Is there any other way to determine if the balancer has deteriorated ie Shoud I remove the serpentine belt and feel for play in the balancer pulley?
Wobbling Crankshaft Balancer '06 C6 LS2
I knew that I would find someone with the exact problem... I noticed a faint chirping at idle on my 32k mile '06 C6 last week and popped the hood to take a look... Using a make-shift stethoscope I started probing around the Alternator, water pump, etc. and couldn't isolate the location that the sound was coming from. Then while checking the belt for abnormal wear and travel, I noticed the Crankshaft Balancer "wobbling" slightly and knew that was abnormal.
Bare in mind I have years of maintaining my 18 daily drivers and 7 different race cars in the past 35 years. But this is the 1st and only LS2 engine I've had.
So, last night I went on a internet mission to fine the answer and came-up with the same information you posted. But have yet to find a reputable source GM rep or Master Mechanic who says, without impunity, that the wobble is normal and acceptable.
I'm going to keep searching for the answer, but in the meantime I've had a racing buddy convey multiple stories of the rubber separating from the Crankshaft Balancer of the LS2's and causing a domino effect of destruction to the belted components under the hood.
Thankfully the C6 is a weekend warrior and occasional "showroom stock" road racer so I'm going to let it sit until I find a suitable answer...
I finally brought my '06 to the dealer and one look at the wobbling balancer elicited the response, "Holy crap, I've never seen that before! You've gotta get that fixed!"
Originally Posted by HDDP
So next comes the quote for $500 in parts and $800 in labour for a whopping total of...Well, you can add. And of course there's no 5yr powertrain warranty on '06's.
The car only has 40,000 km (25000 mi) on it. I don't race it. I don't even rev it over 5K rpm!!
Anyways, besides my wife killing me ("I know this car is an extravagance, Dear, but it will easily give us 10 years of troublefree fun!") , I am going to post to the Corvette Forum on the off chance that anyone there has received GM Goodwill Assistance.
A quick followup... I have discovered something VERY interesting! The part number I was given by my dealer was GM12635652. Apparently, GM Canada has ZERO inventory of this part. So I phone a dealer in Ogdensburg NY and I was quoted $230US (less than half the price quoted by my dealer - given our dollar's parity with the US this is really annoying but I digress) and guess what - GM US has ZERO inventory of this part as well!!
Originally Posted by bryan_p
This is highly suspect given that the LS2 is used in a host of vehicles including the Pontiac GTO, a number of Holden (Australia) vehicles, Cadillac CTS-V, Trailblazer and even Saab. So, either there has been a rash of repairs which has depleted inventory or GM has pulled the part off of it's shelves in order to assess their early failures. In either case this gives hope for a GM hidden warranty.
Suspicious indeed ! The only other possible scenario I can add to it's unavailability is possibly the part is mfg'd in Japan and the supply chain is temporarily broken...
Originally Posted by bryan_p
That being said, I have a speculative theory on the early and widespread failure of the part.
Based on multiple internet references from many LS2 model specific forums, the first time people notice the "balancer wobble" is when the car develops the telltale "chirping". Then, while investigating the source of the "chirp" they notice the infamous "Wobbling Crankshaft Balancer". Those who take it to the dealer for diagnosis usually end-up with a belt replacement that temporarily eliminates the "chirping" for a month or so. This "Drive Belt Chirping Diagnosis" diagnostic & repair procedure is spelled-out in vol. 2, page 6-45 of the Tech Manual.
I have also found a few anecdotal references online of switching the belts to Goodyear Gatorbacks and eliminating the problem permanently. So, this weekend I opted to experiment with the Gatorback belt replacement and this is what I found.
Based on the Tech Manual "chirping" diagnosis procedure #3, it is recommended to remove both belts and operate the engine for 30-40 seconds to determine if the chirp is eliminated. So, prior to removing the OEM belts I "scored" the face of the outer and inner mechanisms and put a dab of white paint on the rubber bushing. Then I measured the runout of the outer mechanism "balancer / pulley" at 800 RPM idle. The runout was appx. 2 mm while the inner mechanism was zero. And the "chirping" sound was still present.
I then removed the belts, started the engine and repeated the measurement with a result of appx. 4.5 mm runout on the outer mechanism and again zero on the inner. The "chirping" was eliminated completely. This was an increase of 2.5 mm's of "wobble" just by removing the OEM belts and letting the Crankshaft Balancer spin free at 800 RPM.
I then installed the Goodyear Gatorback belts which are much beefier belts than the OEM and fit much snugger than the OEM belts which had 32,500 miles on them. This is probably due to wear and stretching over the years.
Again, I fired-up the engine checked the dash for a CEL or SES light and listened for the "chirping". Thankfully it had gone. Then I examined the pulleys and belts to make sure they were seated properly and while doing so, noticed a decrease in the balancer "wobble". I measured it again and the "wobble" had been reduced to appx. 1 mm only. And almost looked like a solid crankshaft balancer.
This got me thinking about the design and assembly of the balancer and what effects tightly vs. loosely fitting belts would have on the bonding and tensile strength of the rubber bushing between the rubber to metal mechanisms.
My hypothesis is that as the OEM belts age, they stretch slowly which progressively lessens the pull / stiffness on the Crankshaft Balancer assembly. This allows the outer mechanism to float or shift on the rubber bushing due to centrifugal / torsional forces causing the rubber to soften / flex and the metal to rubber bonding to weaken from constant movement thus allowing the balancer to "wobble" which as it worsens, causes the chirping belts which eventually leads us to discover the "wobbling" balancer.
In conclusion, If the OEM belts were replaced before they stretched to the point of allowing the balancer to shift on it's rubber bushing, would this prevent the ultimate failure of the Crankshaft Balancer Assembly.
Perhaps GM should install belts that are a bit less likely to stretch in such a short period of time, or they should require the belts be changed at regular scheduled maintenance intervals before the loosened belts allow enough play for the Balancer to start softening the rubber bushing and it's bonding agent. Because I believe when the balancer gets to the point of having enough runout "wobble" to cause the belts to chirp, it has gotten to an inevitable failure state.
Very thorough diagnostic! I suspect that the problem is caused by a combination of belt stretching (length and width) and balancer rubber aging. I also wonder if the belt develops "soft spots" which allow the belt to twist in certain spots along its length. This aging is probably worsened by winter storage since the balancer is in a fixed position with tension applied in a single direction for long periods of time. Do you store your vehicle? Are you taking a wait-and-see attitude or are you pursuing a balancer replacement?
Originally Posted by HDDP
I'm going to try the Gatorback swap although I agree that the balancer failure is probably imminent. Frequent belt changes and the removal of belt tension during storage may prevent this from happening in the future.
I'm going to take a wait and see attitude for a few weeks just to quench my curiosity. But, I run the car with NASA "National Auto Sports Association" in TTU class appx. 8 weekends per year and I won't it on a road racing circuit again, until I replace the potentially faulty part. I'll probably go with the an aftermarket balancer now that I am aware of this problem.
PS: FYI the Goodyear Gatorback part #4040400 for the AC belt is wrong on Goodyear's site and many other vendors. The two belts you want are (MAIN DRIVE BELT) 4060798 and (A/C BELT) 4040410. Here's a link that explains it in detail.
Goodyear Gatorback A/C belt -Wrong Part Number - Corvette Forum
Thanks for the heads-up on the part number. I just replaced the belts last night. The Gatorbacks are definately more rigid than the oem belts. The chirping is gone, even when cold! The wobble is still there but I just want to enjoy the car so I'll keep an eye on it to make sure it doesn't get worse.
Originally Posted by HDDP
The three most popular aftermarket replacements I have seen in forums are Powerbond, SLP and ATI. The ATI is too expensive but Powerbond and SLP only offer %25 underdrive versions. My steering tends to balk under low-speed (parking lot) turning situations so I'm thinking that a stock or %10 underdrive pulley would be best for me. Powerbond makes a %10 underdrive (PBU1117-SS10) but I'm not sure it will fit the LS2 and the performance shops up here in Canada don't seem to know much about this topic. Let me know what you find.
Too bad your out of warranty. I took mine to the dealer and had it fixed. It was covered under warranty. They said it had to be obvious that it's wobbling. Mine wasn't making any noise yet but it was wobbling.
Funny thing is the one they put in replacement of the old one seems to have a small wobble to it and I'm keeping an eye on it to see if it gets worse. I should have just purchased a under drive or lightened pulley for a replacement instead...
i have the same problem and im tryng to get it fixed as we speak ! good thing is that i bought insurance for it and have a 50$ deductable. ! i took it in about 2 weeks ago and the noise was gone but for like a week. ! they balanced the pulley and it was still wobbling, the guy said it was normal on ls2 vettes?!?!?? so i took it back monday and they replaced the tensioner . and i was gonna go pick it up today and the shop said now it has a bad water pump. !
It's funny cause the mechanic and service adviser said the same thing. "It's a Chevy thing it wobbles" I also own a Acura TSX and it doesn't wobble, neither did the other 10 imports I've owned in the past. Except for that one lexus that harmonic balance pulley split apart and just came off. First domestic vehicle and it's not looking so well so far.
First, the prevelance of this condition is there.
Second, there is NO SPECIFICATION for runout on the c5 or c6 harmonic balancer.
Third, rubber isolated harmonic balancers are known to rotate at times in some applications.
The AC belt is usually the first one to make noise as it has the weakest tensioner. Excessive runout in the balancer magnifies the noise when cold.
I have also installed BRAND NEW balancers that have had wobble.
The key, is accurate tension of the belts and alignment with the other pulleys.
My rule of thumb is 1/32 inch runout maximum.
You wouldn't believe it but it's starting to wobble again! It's only been 2,000 miles since it was changed last. Heard chirping noises at high RPM and shifting into the next gear. Looks like I drive mines too hard? Going to try for a second warranty...I fear there will be a third and more....this time it's a different direction it's wobbling in...looks like a egg when the cars on, the old pulley was like a bent bicycle rim.
The purpose of the harmonic balancer is to absorb excess imbalances. These imbalances are the net of all dynamic movements of all components. Theoretically, if all moving components of the engine were made exactly to specification and all engine block mounting points were manufactured precisely to spec, there would be no imbalance. The harmonic balancer would have no imbalance-caused vibration to absorb.
Each component has its specific +- tolerance. The engine as a component has an imbalance that is the sum total of all its components' imbalances.
If the sum total of all moving and rotating components have a net out-of-spec that is greater than the harmonic balancer is designed to isolate and still remain functional, then the balancer itself can fail repeatedly. It would fail because it is performing its job. Its problem would be that it was not designed to absorb so great an imbalance -- that is, the net imbalance created by this engine.
It may be possible to isolate and identify a specific component that is so much out of balance that it causes the net imbalance to be great enough to continue to destroy GM harmonic balancers built to absorb most out of spec combinations, but not your engine's total out of spec imbalance.
Technical Writer for Internet & Print Media
Originally Posted by PeterG
First of all, though lots of people use the term, this part is not a "harmonic balancer". It is a "harmonic damper"...big difference.
If we're going to have a technical discussion of this device, we need to, first, understand it's purpose and function.
The primary purpose of a harmonic damper has nothing at all to do with engine imbalance or balance. Though some external balance engines use the damper rim for engine balance that is a secondary purpose.
The primary purpose of a harmonic damper is to damp harmonics generated in the crankshaft by the engine's firing impulses.
Without a hamonic damper, the crankshaft tends to act like a torsion bar. Firing impulses applied to the crankshaft tend to "wind" this torsion bar, which responds by unwinding then re-winding in the opposite direction. Usually, these torsional forces are damped naturally, but at certain engine speeds the impulses from the cylinder firing are in synch (or in harmony) with the crank's natural resonant frequency. At those speeds harmonic vibrations will damage the crankshaft.
In an automotive engine there is little control over operation in those rpm ranges and there will be annoying vibration as the engine is operated through such rpm ranges and usually, there are durability problems if the engine is operated for any length of time in those ranges.
The harmonic damper damps those harmonics and eliminates objectionable and potentially damaging vibration.
Now, because the damper rotates at engine speed, it must be balanced so as not to create a vibration of its own. Some external balance engines use an out-of-balance damper to balance a rotating assembly which would otherwise be out of balance, but again, the primary purpose of a harmonic damper is to damp harmonics in the crankshaft set-up by firing impulses not to dynamically balance the rotating assembly.
As for the wobbling balancer discussed by the OP..replace it.
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