Has anyone heard of a serpentine belt just breaking on an 03 MCS, this happened to me last thursday on my way to work. All of the sudden I'm cruisin, then no power, hit the hazards, and moved to the shoulder. A good thing that I was only about 1.5 miles from work, and I had buddies that could help me, tow it to a repair shop, they charged me $130 to replace the serpentine belt. I thought that was a good price considering the alternative of having it towed to Mini, and them bending me over the table to be raped. The repair shop said that I shouldn't have broken, due to the car only had 28K. I told him that car is 5 yrs old, and the belt is stressed from the supercharger. The serpentine belt has never been changed. Since I have a 15% SC pulley, could the belt tensioner be a likely cause? Not exerting enough tension on the Serpentine belt. My car has alot of performance work done to it. I think that the belt broke due to stress and old age. tell me what you think? If you are ever in Dumfries VA and need a belt replaced on your Mini, then Daniel's Auto Care on Rt 1 is the place. Good work cheap price.

 

It's not uncommon. I replaced my belt around 65k and found a giant chunk out of it but I didn't have a reduction pulley. With a reduction pulley there is going to be more stress on the belt. Many people put on the JCW belt as it is better matched with a reduction pulley than the standard belt with a reduction pulley. Alta has smaller belts as well as a belt tensioner stop as a safeguard to prevent damage to the idler in case the belt snaps again. It does happen and that's why companies make products to try to minimize the damage if it occurs which it will. If you do a search you'll find a lot on the subject. As long as the shop said the belt tensioner is fine, you should be ok for another 30-60k. If stock the dealership would have replaced the belt at 60k, but it should be done sooner if you have engine mods and drive more aggressively. My belt looked like this when I took it off at 65k:

 

Thank you brother for your insite. The idler pulley is fine just a little nicked up when the belt broke. I will use your advice. And thanks again.

 

Why would a smaller reduction pulley put more stress on the belt? The belt is not moving any faster is it? If you put a different crank pulley on it then the belt would be moving faster. The only thing moving faster is the supercharger.

 

The belt wraps at its most severe angle around the SC pulley. A smaller SC pulley forces the belt to bend at tighter angle... which will wear/age/stress the belt faster, even though the belt itself isn't moving any faster. It's well documented that 19% pulleys eat belts faster than 15% pulleys....

Many folks with reduction pulleys replace their belts proactively ever year or two... regardless of mileage...

 

Blimey's got it right. Another reason is that although the original belt tensioner should keep the belt taut even with a reduction pulley some people have had the belt "walk" across the pulley or slip a bit when turning causing greater friction or wear. A shorter belt would alleviate the angle issue the Blimey described as well as allow the tensioner to work as it was designed and have the belt be better seated on the SC pulley. You're running with a belt that is longer than the distance it was designed to travel and the tensioner should compensate but its best to just put on the right belt.