Harmonic Balancer

[SIXt7]

I'm getting a vibration, especially noticeable on the inside rear view mirror, when I rev the engine while in neutral. Motor mounts are tight and look ok. Is this normal or is it perhaps the harmonic balancer? If it is the balancer, how difficult is it to replace...better to get new or rebuilt? Engine is 1967 327/350, completely stock, no power steering, no air ,about 48,000 miles. Vibration is intermittent while cruising but noticeable when it gets the gas. Also, I plan to replace the water pump..top pulley is wobbly at idle...any connection to vibration? Thanks.

 

[WayneC]

Easy to find out... replace the water pump before the fan goes through the radiator, then see if you still have a vibration.

Vibration could be due to an imbalance in the flywheel, a slight miss in one cylinder, bad motor mounts, fraying or loose belt, bad bearings on an alternator/accessory, etc. Frankly I'm not sure how you'd determine a balancer is bad unless you can see that the outer ring has slipped on the rubber, either rotationally (throwing timing mark off), or it's moved forward or rearward. The balancer doesn't actually eliminate vibration, just reduces/softens it.

A replacement balancer is #3817173 ($77 at gmpartsdirect), or you can have the original one rebuilt. To remove the old one you will likely need to remove the radiator to gain working space from below the car, then remove a crankshaft bolt and the pulley(s), then a puller is required to remove the balancer from the interference fit on the crank.

 

[JohnZ]

Take the fan belt off and fire it up to eliminate accessories as a possible source of the vibration - takes about two minutes.