Snapped Belt

[wakebrd21]

I need some help with the GT40 in my 97 Super Sport. As we accelerated away from the dock today I smelt burnt rubber coming from the engine. I stopped to investigate but didn't see anything. As I started to pull some tubers I smelt it again and then a belt snapped. My wife tried to pick up the belt and she said it was extremely hot. Obviously it got so hot that it snapped. What would have caused this. I posted a picture below of what belt it was. It's the one just dangling there. These are fairly new belts as well. Thanks for any tips.

[Woody_tobius_jr]

Anything seized? Idlers, alternator still spins? If you smelled rubber burning , chances are something isn't spinning... My .02

[ES]

Also check if any of the pulleys have any give. One of the bolts on a pulley snapped on my engine and it was enough for the pulley to oscillate while spinning and tear the belt (plus burnt rubber smell)...

[wakebrd21]

The belt that spins the alternator is the one that snapped. Does that help spin anything else?

[Woody_tobius_jr]

Sorry, I didn't notice last night, but you have a tension bracket on your alternator, so chances are you won't have a belt tensioner on that belt loop( circuit). Does the alternator pulley spin freely, maybe see if there is an idler in the loop? I'm not sure what all else could have been in the loop for that belt, whether it just comes from the crank directly or if it catches the fresh water pump or the circulation pump. If you have your owners manual, it should have a drive belt configuration diagram in it, and it may help you chase down what all was in that loop.

[wakebrd21]

I checked the alternator and it spun freely with no problems. I'm also having a hard time finding the configuration for the drive belts but I think it connects to two of the other pully's that the other belt is still connected to.

[LakeMorey]

I am trying to diagnose the same problem. GT 40, 1996 Super Sport. Belt burned off. I installed a new belt, now no voltage....thanks for your help!

[DanielC]

What kind of electrical accessories are you guys running in your boats? Do you listen to the stereo without the engine running, and drag the battery down? Are your boats moored for a period of time, and have to sit with the bilge pump on?

If your battery gets discharged, the alternator puts out a lot of current to recharge it. The alternator has to use power from the engine to create this current, and that puts a heavy load on the belt. If the belt is slightly loose, it will also slip when the alternator is trying to recharge the battery, and this will increase the wear. When the belt wears, it slips more.

V-belts can also only transfer a limited amount of power. This is why more modern engines use serpentine belts, with automatic belt tensioners. If the pulleys have rust on them, this will also accelerate belt wear.

The raw water pump belt goes closest to the engine on my 1997 GT-40. It is the longer of the two belts, the raw water pump pulley is bigger than the alternator pulley. It goes around the crankshaft pulley, the circulating water pump pulley, and the raw water pump pulley.
The alternator belt goes around the crankshaft pulley, the circulating water pump pulley, and the alternator pulley. This belt needs to be tighter than the raw water pump belt, or the raw water pump belt can be looser than the alternator belt

[jonsquatch]

If it was burning the belt and it was the correct belt in new or excellent condition and nothing was rubbing against it then it was slipping. This can only happen if something is not turning or not turning fast enough, something is out of alignment, or the belt was too loose. The alternator is used to adjust tension on the v belt in that picture. It looks to me that the head of the adjustment bolt has been rounded off a bit and it is also situation such that it is about 1/4 as tight as it could be. If it was still in the "tight" position in that picture there is not much adjustment left to get the belt on and off. If the bolt was a little loose and it had just started to slip it could have started spinning and eventually thrown the belt. Before you loosen it see if you can move the alternator and pay attention to how tight the bolt is when you do loosen it, if the bolt is rounded off to where it doesn't allow you to tighten it enough then replace it.

If your water pump and alternator turn as freely as they should (even if they turn if there is too much resistance then the belt can start to slip prematurely) and also have no play side to side and you get a new belt when you put it on make sure that it lines up nicely between all the pulleys if the bearings are starting to go or the bracket is bent on the alternator and they aren't operating in the same plane it will cause the belt to wear heavily on one side of the belt which will cause it to fail prematurely. If its due to bad bearings or a bent shaft then the offending item needs to be replaced. Sometimes you can put a straight edge across the face of the pulleys to see if they are in alignment sometimes you just have to eyeball it.

[JayG80]

A couple of weeks ago - same thing happened to me as far as black smoke goes. I stopped the engine before the belt broke. It was just loose. Tightened it up and all is well

[wakebrd21]

JayG80. What exactly did you tighten?

[JayG80]

JayG80. What exactly did you tighten?

Tightened the alternator. Alternator belt was hot. Loosened the alternator and pulley spun freely. Tightened up the belt and no problems since then.

[JayG80]

JayG80. What exactly did you tighten?

Tightened the alternator. Alternator belt was hot. Loosened the alternator and pulley spun freely. Tightened up the belt and no problems since then. I also made sure all pulleys were aligned

[wakebrd21]

Ok thanks. I ordered a new belt from nautiqueparts.com. What is the best way to put this on since a post earlier mentioned there isn't a tensioner?

[DanielC]

Loosen the top bolt on the alternator. Swing the the alternator to the engine pulleys. Put the belt on. Pry the alternator away from the engine pulleys, and while holding the alternator there, tighten the top alternator bolt.
Firm pressure in the belt between the circulating water pump pullet, and the alternator pulley should deflect the belt about 1/2 inch.
Recheck belt tension after about 10 minutes, and at the end of the first day of use.