R56 Fraying belts after alternator replacement
 

Long story, but I'll try to keep it short. 2008 Mini Cooper (base) with only 57k miles. Multiple issues in last 8 months of ownership. Latest was bad alternator, which also toasted the battery (over voltage). I replaced both. I replaced the alternator with re-manufactured unit by Pure Energy (they claim it is a 120 amp Valeo model), which corrected the voltage problem. While in there, I decided to also replace the belt as it had some cracking in the ribs. I used a Gates belt. It shredded badly in less than 10 miles. I got a replacement, and it lasted less than 20 miles.

Both belts were installed properly on the pulleys and tensioners. Both tensioners look OK visually. I cleaned the pulleys (what I could get to anyway). Visually, the alignment looks OK, but it is hard to tell for sure. The spacing of the ribs on the belt is correct. The ribs on the new belt are not quite as tall as the original belt, but they seem OK to me.

I am a DIY, with a bit of experience, but relatively new to Mini's. I'm not sure where to go from here. Any advice will be appreciated.