Alternator Belt Keeps Breaking?? WTF??

So I've gone through 2 brand new alternator belts in the last 2 months. Boat is a '97 Nautique Super Sport with the fuel injected 351. The alternator and water pump spin freely and there is no play in the pulleys at all. Visually, the alternator/pulley seem to be in proper alignment. But every so often (maybe once in every 4 outings) you can smell smoke coming from the belt squealing. Turn off the boat, let it sit for a minute, start it up again and it's fine. This weekend we went through 5 sets, then I was riding with my buddy driving and he stopped because he smelled smoke. Turns out we snapped the alternator belt again? I'm not sure what is going on? Anybody have any advice? Is there a clutch on the alternator that I don't know about?

I had this exact same problem with the same motor on my 97 SunSport. I was breaking a belt pretty much everytime I went out. It needs to be installed as tight as you can get it by pulling on the alternator and then tightening it up. I know this is contrary to how you would usually install a belt but when I was on belt number three I launched and the belt started to squeal so I stopped and got it as tight as I could by hand it hasnt slipped since.

(Message edited by maxx_wake on August 25, 2008)

Are you running the stock alternator or have you upgraded to a larger unit?

If you have installed a much larger alternator then it might simply be the case that the single belt is not sufficient. Going past 100 amps on a single belt is risky.

If your alternator is less than 100 amps then I would guess that you have a bearing going out, either on the alternator or on the water pump. I would guess water pump. By chance, is there a water leaking from the pump? Note that this would be the circulation pump, above the main crank pulley, not the raw water pump which would be mounted lower and driven off a separate belt.


Rod

J was that you out on Sammamish on Saturday up at the north end?

Check your alternator pulley for rust. I just had a belt break after 20 hours on my 97 sport w/ the 351. Was getting a lot of belt dust.

I noticed rust on the alternator pulley. Just smoothed it out w/ 600 grit wet sandpaper. Hope that fixes it.

I had this issue when my impeller was so bad and stiff it wouldn't spin in the housing. Did you check the impeller to make sure it's good.

The other time that happens is when the alternator is not in alignment. Did you put in a new alterantor?

Brett -
yeah that was me...really enjoyed the giant rollers you kept throwing me while I was getting burned trying to re-install the impeller belt which flew off when the alternator belt broke

That was you in the Mobias correct?

And as far as I know, that is the stock alternator on there. And there is a little rust but hardly any.

put a str8 edge on the pulley, to make sure the pulley are close to each other, and not to over tight on the belts. feel each pulley on the outter edge to ck for anything sharp. Kenny.

There was a supply of pulleys that were manufactured with the wrong off-set specification. The measurement was only .5mm, but it shredded belts on the 315 hp Mercs. You may have a similar issue. If there is even a slight mis-alignment, you will have your problem.

^^^^yep... i still get centurion with that problem.