So for the fourth time in a year, my alternator v-belt came off while I was driving and my engine overheated, though briefly.

I had a mechanic at an Exxon install the alt - 100 amp chrome silver bullet. Only 3 weeks after it was installed, the belt started squeaking – then last Friday it snapped off. When I first heard the squeaking, I checked the belt and it looked fine - no wear, and it was still tight.

After I pulled over Friday, the belt somehow managed to hang on and it looked like it had been cut crosswise with a pair of scissors - almost a clean break. Further, there was no obvious sign of wear on the belt and I dont remember seeing any belt shavings/dust like I had last time but I do remember smelling an odd burning smell before it came off - when I saw the engine temp shoot up.

It was raining and the pulley is chrome and thus likely got very slippery. I havent trusted the alt since I bought it as the pulley groove is very shallow and the belt sticks up about 2mm from the top of the pulley groove. I tried multiple belts and none would fit all the way into the groove as the belt angle would have needed to be 40 degrees (and v belts only come as 36 or 38 degrees). I saw pics online of installed silver bullet alts and they all showed the belt sticking up like mine so I thought it was ok.

But I cant find a single other person on the internet using a silver bullet alt that has mentioned ever having had any problems with it. Seems to just be me.

Did the rain cause it to slip off, is the alt pulley just not safe to use, or was it the belt I was using (it was a 36” belt). In order for the belt to be properly tightened with the brackets I was using, I had to buy a 36inch belt – 40 inch ones were way too loose. Any ideas?

 

how tight do you have it? i think with the stock alternator it should have an inch of up and down movement.

 

I had it tightened to 1/2 an inch. Like I said above, I really am starting to think that it was the rain as the pulley - even the inside groove - is covered in chrome making it really slick. Plus no belts would fit all the way down into the pulley and the night it came off it was raining - so I'm thinking it had at least something to do with the rain. I'm changing it and putting on another 1 -wire, 100amp alt, but with a pulley the same size, design and material as a stock one.

 

Put a straight edge against the front of the pulleys to see if they line up. They may be a little off line.

 

Seems likely to be the problem. With good alignment, you can run even the wrong size belt for years.

 

I had a similar issue like that with my 1971 Grande. After replacing the altenator, the belt snapped within 100 miles. Turns out that with the new altenater, the belt was aprox 5mm out of linement.

 

see if the belt lines up (as above). for tighteness is good when you can twist the belt around it's own axis by 90 degrees max with thumb and index finger

instead of chaning the alt, try changing the pulley to stock one. Slippery will cause belt to squeak, but not to break

 

I can imagine in my head that a slick pulley COULD cause the belt to break...

Imagine the belt slipping over the slick wet pulley until the heat from the friction (a lot of heat real fast) flash boils the water, the hot (and now sticky) belt suddenly catches HARD and SNAP...

I could see this happening even more with a big electric fan or a thumping stereo loading up the alternator, and even more so if the belt is not riding on the shoulders of the sheave.

 

I can imagine it as well. But Occam's Razor would suggest the misaligned pulley, which is the first thing i'd check.

 

The pulleys are out of alignment. Having the belt a little out of the top of the pulley groove doesn't matter. They do that on my racing pulleys and I turn them to 8,000RPM without issue, but a little misalignment will chuck a belt off faster than anything. I do about 1/2" of flex in the belt tension for a race car, could get away with a little more on the street, never an inch, thats too much.