Alternator belt keeps breaking

I need some help. The belt driving my alternator keeps breaking and I cant figure out why. I have gone through three belts in the last 2 weeks. Everything appears to be inline but that is just from a visual inspection. The boat is a 97 Supra with a PCM 351 HO. Basically the belt that keeps breaking only goes over the two large pulleys in the center and then over to the alternator. I did notice some melted rubber on the top most pulley in the center (oil circulation pump?) but I am not sure what this means. The raw water pump belt goes over these same two pulleys and it has not had any problems. They are both V belts.

Chris,
Check the belt tensioner my bet it is not adjusted properly, or it could be your pulley may be out of balance, my suggestion is to take it to your nearest boat shop and they should be able to correct it in a matter of a few seconds

since your other belt is not breaking I'm going to guess that your alternator shaft is bent or you are severely over tightening your belt

I think you might be right about the shaft being slightly bent. The last belt was a clean break but the whole belt felt like it was stiff and brittle. This makes me think it was stretching and contracting a lot which would be indicative of a bent shaft. Is that something that can be fixed or will I need a new/rebuilt alternator?

How does your groove the belt sits in of look and feel on your alternator? For some reason, my cousin's old Sport Nautique had an alternator pulley that rusted frequently. He had to sand it down or it would eat alternator belts.

You can check for a bent alternator shaft using a dial indicator. I don't know what range would be considered OK though. You can get a new shaft but you need some special tools. By the time you get the shaft and tools, you might as well have someone rebuild it.

I worked in a shop that repairs alternators and starters through college and replaced repaired 100's of alternators. Never saw a bent rotor. The rotor shaft is very short, supported on both ends with bearings. No way to bend it in the boat. I saw numerous times where bearings fail and allow the rotor to rub inside the alternator against the stator causing the alternator to be hard to turn and destroy the rotor and stator.

Either alignment, rust, tight bearings, or over tight belt is causing the problem.

When you have the belts off does the alternator spin freely? The water circulation pump (top pulley)?

Are the grooves clean on all of the pullys?

(Message edited by mobv on August 04, 2008)