2002 5.3 Crank appears to wobble at idle

[rockola1971]

I'm not following you. Are you saying that a belt slipping or falling off can cause a crankshaft on the LS engines to snap? I don't really see that happening under regular driving conditions.

On these engines the crankshafts are internally balanced to the rotating assembly. The harmonic balancer is not to balance the engine, only dampens small vibrations (or harmonics). That's why is not keyed in. The flexplate is not indexed either like some of the older engines or had a counterweight on them. Accessories are not balancing the engine either, and are usually only dragging down a small percentage of the engine power.

A lot of the 70s and 80s engines had gray cast iron cranks that were very brittle and these are times before advanced computer modeling such as Finite Element Analysis was developed. Coupled that with externally balanced design, I can see a belt coming off causing issues on those engines.

Edit: typed this last night and now see @2006Tahoe2WD Seems like we are saying the same thing about the harmonic balancer...

Not referring to a vbelt or serpentine belt. Referring to the rubber belt sandwiched in between the inner and outer portion of the harmonic balancer. You stick a severely out of a balance hunk of metal (What happens when the belt slips) onto the end of a crank and that crank will be stressed across its longitude and at the bearings. Nothing good will become of it.

Troubleshooting Harmonic Balancers • The Original Fluidampr

10 signs of stock elastomeric harmonic balancer wear. Learn why they wear down and when to upgrade to a quality viscous type harmonic balancer.

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[exp500]

Do a quick read on 3rd order harmonics, it's all about frequency. Why does a real race engine cost $100k+? It's all the little details.

 

[2006Tahoe2WD]

I'm taking the Tahoe in this morning to have the HB replaced. I'll report back. Fingers crossed. I hope it runs truer and maybe a strange noise sometimes at idle will be gone. We'll see.

I checked the new HB today and it runs truer than the old one that's for sure.
The tension pulley for the AC bounces less. It looks like there is a bump of some sort in the belt.

 

[2006Tahoe2WD]

Today I got time to check how true the new HB looks. Looks pretty good, definitely better than the original 16 year old one. It was cracked around the rubber that shows. The AC tensioner runs with less bounce. I think the bounce there is a "bump" in the AC belt. Right now I'm using the green Gates belts.

 

[rockola1971]

Today I got time to check how true the new HB looks. Looks pretty good, definitely better than the original 16 year old one. It was cracked around the rubber that shows. The AC tensioner runs with less bounce. I think the bounce there is a "bump" in the AC belt. Right now I'm using the green Gates belts.

Check to see if the front face of the inner and outer hub of the old HB are true to one another or has the outer ring moved inward or outward?

 

[2006Tahoe2WD]

Check to see if the front face of the inner and outer hub of the old HB are true to one another or has the outer ring moved inward or outward?

I didn't get a chance to do that. The old part is now gone. I assume the rubber got so old that it deformed in some manner causing the outside part to no longer be true to the inside/hub part. As mentioned the new one is running truer.

 

[2006Tahoe2WD]

At this point I'm starting to think the HB is a wear item. I'll say 100k miles. You replace the seal also.
I had a strange vibration noise before the replacement and yesterday I didn't notice it. We'll see how it goes.

 

[2006Tahoe2WD]

This is an old thread. I had the HB replaced and I still notice what looks like to much runout. I'm thinking I wonder if there is a spec. on the runout. There is! Looks like the allowed runout is 0.40mm. Measured with a dial indicator.
What do you guys think?

Here is the copy and paste....

#PIP4750E: Belt Squeak Noise And/Or Crankshaft Balancer Appears To Wobble - (Feb 10, 2012)
Subject: Belt Squeak Noise and/or Crankshaft Balancer Appears to Wobble

Models: 2010-2012 Chevrolet Camaro SS
2011-2012 Chevrolet Caprice
2009-2012 Chevrolet Corvette
2008-2009 Pontiac G8
with 6.0L 6.2L Engine (RPOs L76 L77 L99, LS3, or LS7)

--------------------------------------------------------------------------------

This PI was superseded to update recommended field. Please discard PIP4750D.


--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may complain of a belt squeak noise and/or a crankshaft balancer appears to be out of balance or wobbling while watching it with the engine running. In most cases, the wobble is an optical illusion because the design of the balancer gives the appearance that it is moving more than it actually is.

Recommendation/Instructions:
If this concern is experienced, follow the steps below:

 1. Push the crankshaft all the way to the rear of the engine.
 2. Using a magnetic base, attach a dial indicator so the measuring tip is contacting the rear of the drive belt groove.
Notice: An inaccurate reading may be obtained by measuring the face of the balancer instead of the rear of the drive belt groove.

 3. Rotate the crankshaft 360 degrees and note the total amount of crankshaft balancer run out.
◦If the balancer run out is 0.40mm (0.0157”) or less, do not replace the balancer because the run out is in specification.
◦If the balancer run out is greater than 0.40mm, replace the crankshaft balancer and perform step 3 again to confirm that the run out of the new balancer is in specification.
 4. If the customer has complained of a belt squeak, also replace the drive belt.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

 

[OR VietVet]

This is an old thread. I had the HB replaced and I still notice what looks like to much runout. I'm thinking I wonder if there is a spec. on the runout. There is! Looks like the allowed runout is 0.40mm. Measured with a dial indicator.
What do you guys think?

Here is the copy and paste....

#PIP4750E: Belt Squeak Noise And/Or Crankshaft Balancer Appears To Wobble - (Feb 10, 2012)
Subject: Belt Squeak Noise and/or Crankshaft Balancer Appears to Wobble

Models: 2010-2012 Chevrolet Camaro SS
2011-2012 Chevrolet Caprice
2009-2012 Chevrolet Corvette
2008-2009 Pontiac G8
with 6.0L 6.2L Engine (RPOs L76 L77 L99, LS3, or LS7)

--------------------------------------------------------------------------------

This PI was superseded to update recommended field. Please discard PIP4750D.


--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may complain of a belt squeak noise and/or a crankshaft balancer appears to be out of balance or wobbling while watching it with the engine running. In most cases, the wobble is an optical illusion because the design of the balancer gives the appearance that it is moving more than it actually is.

Recommendation/Instructions:
If this concern is experienced, follow the steps below:

 1. Push the crankshaft all the way to the rear of the engine.
 2. Using a magnetic base, attach a dial indicator so the measuring tip is contacting the rear of the drive belt groove.
Notice: An inaccurate reading may be obtained by measuring the face of the balancer instead of the rear of the drive belt groove.

 3. Rotate the crankshaft 360 degrees and note the total amount of crankshaft balancer run out.
◦If the balancer run out is 0.40mm (0.0157”) or less, do not replace the balancer because the run out is in specification.
◦If the balancer run out is greater than 0.40mm, replace the crankshaft balancer and perform step 3 again to confirm that the run out of the new balancer is in specification.
 4. If the customer has complained of a belt squeak, also replace the drive belt.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

You supplied all this info, great, but did not tell us what your runout is? C'mon man!

 

[2006Tahoe2WD]

You supplied all this info, great, but did not tell us what your runout is? C'mon man!

okay, okay - give me a second. I just found this today. I'm starting to plan how to hold the dial indicator as described. Please stand-by I will report findings.