Harmonic balancer is failing prematurely and requires renewal.... but the retention bolt fails to budge... using an 1/2" drive impact wrench rated at 600 lbs/ft in reverse failed to budge it.

Any suggestions on how to remove this bolt?

Get a 1/2" drive socket that fits the bolt (I believe this is a 17mm Allen head) and the longest breaker bar you can come up with, then use a pipe over the breaker bar. You'll need the tool to counterhold the balancer, the one that engages into the balancer spokes (webbing). In extreme cases you may need to use a torque multiplier.

Gilly

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I used the breaker bar method, except that the breaker bar was pointing downward. I placed my feet on the breaker bar and with my hands on the car frame I broke it free with my legs - It saved my back. The bolt is on very tight, I used blue thread locker on the threads when putting the bolt back on since the original bolt had blue thread locker on it.

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles

Used crank holding tool (Baum Tools, < $100) and 1/2" drive 17 mm Allen head, both equipped with breaker bars... bolt moved immediately. Renewal of pulley took less than 15 minutes.