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2009 - 2012 Corvette Z06: GM TechLink: Drive Belt Noise and Crankshaft Balancer Runout

Source: GM Techlink

Date: October 2011

Subject:  Drive Belt Noise and Crankshaft Balancer Runout

Models: 2009 - 2012 Chevrolet Corvette Z06

On some 2010-2012 Camaro SS models and 2009-2012 Corvette models equipped with the 6.2L engine (RPOs L99, LS3, LS7), a drive belt noise may be heard and a crankshaft balancer may appear to be out of balance.
 
If a crankshaft balancer appears to wobble while watching it with the engine running, it's often an optical illusion due to the design of the balancer, which gives the appearance that it is moving more than it actually is.
 
To determine if the crankshaft balancer is out of balance:
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. Measuring the face of the balancer instead of the rear of the drive belt groove will provide an inaccurate reading.
3. Rotate the crankshaft 360 degrees and note the total amount of crankshaft balancer run out.
• If the balancer runout is 0.4mm (0.0157 inches) or less, do not replace the balancer because the runout is within specification.
• If the balancer runout is greater than 0.4mm, replace the crankshaft balancer and perform the measurement again to confirm the runout of the new balancer is within specification.
4. If a belt squeak is heard, also replace the drive belt.
 
- Thanks to James Parkhurst
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