Need help with 7.4 alternator belt

1997 7.4L Bravo 1. This model has 3 v-belts, not a serpantine belt. Last year, I had to change my sea water belt. When I did this, I decided tp replace all 3 belts since I was in that deep. After a few trips out this year, the alternator belt completely came apart. I replaced the belt again with a new one from Mercruiser, adjusted the tension per specification, and began using again. Within a few hours of operation, it began squealing and I adjusted the tension (tighten). It helped for a bit but it continued to squeal at a fast idle. Went out yesterday and the belt broke again. There is less than 10 operatng hours on the new belt....probably similar to the previous belt. Bottom line, 2 new belts have broken within a few hours of operation. Here is what I've done so far. I have spun the alternator and it seems to spin freely. I have also visually looked at the pulleys and they seem to be aligned. Also, the alternator pulley looks "OK". There is some rust on the pulley but it is not excessive.

The alternator is the original one (1997) but works properly when it is being driven by the v belt. I new one is $256 and I'm not even sure if that comes with new pulleys.

I hate to re-install another one without knowing what the source of this issue is. Although replacing the belts is pretty straight forward, getting to them is a pain.

I am open for any ideas/suggestions.

An alt squeal is indicative of a high charge rate and a belt sitting too deep in the pully

If the problem is the alternator (dragging bearings) you can get it rebuilt for a fraction of that astronomic cost.

Jeff

if there's any roughness on the driven faces of the pulley, the belt doesn't stand a chance....and you're better off using a straightedge to ensure alignment as that will kill a belt in short order, too...

Thanks for the help, all. I have checked the bearings on the alternator and they appear/sound to be fine. I have removed the alternator and dropped it off at a shop this morning. The broken belt is much thinner than it was originally and l'm not sure if it was due to an issue with the alternator or potentially the pulley since it does have some rust on the driven faces. Either way, I will not put the original alternator/pulley back in the boat since it is a pain to do.

I will keep this group informed and thanks for the help.

Ayuh,.... It don't take much rust on a pulley to tear a belt to dust in No time flat,.....

A good paintin' with an industrial enamel, like Rustoleum helps,.... let it dry, 'n harden good,...

Try aligning the pulleys with a straight edge rather than your eyeballs.