After nearly wrecking an OEM belt after 12hrs in a 300whp engine, every motor I touch gets a kevlar belt. I don't even stock/sell the OEM style belt.

I don't lack an understanding of interference vs non-interference.

Now it's quite possible I misunderstood the reason for the thread. From the original post I thought that he could not get the cam gears lined on the timing marks while installing the timing belt because of interference problems. If that were the case, my response makes complete sense.

Check your lifters/shims.

Stock isnt kevlar?

Dear mazda, why you go out of your way to buy non-standard belt thats less good than the standard belt? For modern cog belts kevlar is the standard fiber material, you have to go out of your way to order nylon, at least industrially.

Don't know, actually. All I know is that I put an OEM belt on my first built motor, purchased straight from Comp. 7400rpm, ~320whp max. When I tore it down to rebuild ~12hrs later, the belt was literally falling apart. The internal structure (metal cords IIRC) had breached the smooth outer layer in several places. I've never used another OEM belt.