I have 12 rib M3's. I would think these belts are very sensitive to walking over the edge?? When do I stop tinkering and fire it up? Is 1/16th close enough?

anyone?,,anyone??

If it's not perfect it might not jump but it sure will make alot of rubber "dust" in the engine compart.ment

I had the same problem. Twin engines and one belt kept jumping and destroying the belt. I put a straight
edge from the drive pulley to the driven pulley and found
one engine off about a 16th . I cut the back face of the driven pulley. problem fixed ( or you can add a shim)

stock heads and the spacers were the length ATI said but it was way off,,so was the shim they sent for the lower pulley. The instructions were almost useless and even refered to diagrams that were not there. Bought the kits used so I guess that's part of my savings ,,If I can get it running right I'll be very happy. To remove the drive pulley do I need to put a piece of ?? in the rear impellor to stop it??Thanks,Allen

Hey Cooltoys. I had to take the pulley off mine the other day and I just used an electric impact wrench to take the bolt out of the blower shaft. That way you don't need to hold anything. Just remember to use some locktite on the threads when you screw it back in.
I didn't realize that there was a problem with alignment. I have an aftermarket block and heads (Merlin). I guess I had better check that too.
I agree that the instructions are crappy. (Bad black and white photos of a black merc. engine tends to not be the greatest illustrative tool!)