Gus, I don't remember the size of the bolt However, I have one of those inexpensive Air tools (Santa should bring good one) and it has worked on some and not on others. The ones it did not break it loose on we used the old breaker bar and tap the ignition trick and it works fine. Just support and maybe even pad the handle of the breaker bar and tap ignition.

The harmonic balancer needs two metric and sorry don't remember that size either. I just guessed when at the store and bought 3 sized pairs and one pair worked