Dear Gilly
I have read a number of post regarding harmonic balancer pulley failure leading to extensive damage to the oil pan. How can you check if the pulley is good or not. I know the location of the pulley and know how it loooks like..

The easiest way would be to watch the lower pulley (the crank pulley) with the engine running and see if it seems to not be running true (like a vibration to it).
To visually inspect you wouldn't see all that much. There is an inner "web" shaped portion and the outer pulley, with a rubber section between these 2 parts. The rubber part slips or otherwise loosens up allowing the outer part to seperate from the inner part.

Gilly

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