John, the damper may not be valid. Under the presence of ozone, gas, oil and grease, the elastomeric material that separates the inner hub from the outer ring will begin to break down. When this happens, the outer ring can slip in relation to the inner hub. When this happens, the slot in the outer ring is no longer clocked to the keyway cut in the inner hub and your TDC is no longer valid. Mr. Pope is saying that you can verify that the timing on the damper is about right by timing the motor by ear, then verifying the timing with a light to see if the damper is valid.