A wobbly balancer can be a cause or effect

Question:

In the letter from M. Scott Smith in your December issue, he discussed the various things he investigated to locate the source of a vibration.

One item he mentioned was a wobbly harmonic balancer. I have a slight vibration on my small block Chevy engine at certain mid-range speeds. I recently noticed that at low speeds (idle), the harmonic balancer was wobbly, but as soon as the engine speed increased it smoothed out.

Why would a wobbly harmonic balancer indicate a vibration problem?

If it needs to be replaced, can you please offer any tips to make the project go smoothly?

Answer:

A wobbly harmonic balancer can both be the cause of a speed-dependent engine vibration and the result of one. Either way, the balancer should not wobble.

As a preliminary step, you should determine why the balancer is wobbling. The center section of the balancer should be a press fit on the crankshaft snout. If it’s a sloppy fit, it will wobble and poses a serious safety risk. If the crank snout is damaged then you have a much bigger problem than a bad balancer. A good machinist may be able to fix the damaged crank or you may need to replace it.

The wobble in the balancer can also be due to looseness or misalignment between the balancer’s inner hub and outer ring.

The hub and ring should each be securely adhered to the thin rubber ring between them but sometimes they loosen.

When this happens, the outer ring can shift and wobble. At high engine speed it may even break away from the hub and it can do a great deal of damage if this should happen.

The trick to replacing the balancer with minimal pain is to employ the correct tools. Use a balancer puller to remove the old balancer and a balancer installation tool to install the new one.