My timing belt has 24k plus miles on it. I have carried a spare belt and the tools to change it for 3 years now. I have a Confederate motorcycles clear cover and the belt still looks good. I have to wonder about the wide differences in longevity. S&S recommends a change at 30k.
I believe the differences come down to heat. When my first died, without benefit of the cooling gap in the cover, it showed definite symptoms of blistering on the back of the belt where it would stop on the main crank shaft when the engine stopped. They always stop in the same place just like any 4, 6, or 8 cylinder block. That place was were my belt parted. Ever since I've had the gapped cover there has been no sign of blistering and this belt has outlasted the first by a significant margin.
