belt throwing

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360duster

360duster

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Hi Guys,

i have a mixed set of pulley on my engine, don´t even know where these are from originally. The alignment is good, but it keeps throwing the belt over 5000 rpm....no fun at all.

the lower pulley does not run perfectly, it has got a slight "shake", don´t exactly know how to explain. the belt is around 47" long.

can this cause the problem? How long is the water pump / alternator belt originally?

Michael
 
Oklacarcollecto said:
If all the pulleys are aligned correctly then it is most likely caused by the crank pulley shake.
Click to expand...

I concur with Mr. OK. Also, if the belt is not very stiff (i.e. can be easily twisted), then it is much easier for the pulleys to throw it off. Try to get a heavy duty stiff belt of the same size and make sure you get it tensioned correctly.
 
What engine are you using? And what style pulley system?
 
engine is a Stroker SB, pulley system is the same layout as the stock one...it seems that the crank pulley is from AC-car (3 groove), i adjusted the alternator to be in line with it.....

Michael
 
How is your alternator mounted? Is there any flex to it? Short of a bent pulley, I would suspect a bracket flex. Also check HOW your belt is riding in the grooves. If it is riding high, it is much more likely to get tossed.
 
Thanks guys, i´ll try to get a matching set of pulleys from a non ac car and the factory Alternator brackets. Hope this will cure the problem.

Can someone tell me the specs for the original belt?

Michael
 
Had a 340 years ago that did the same thing. Aligned pulleys heaps of times, ended up being a birdcage alternator that had a slightly bent shaft and would throw belts off at high revs. Can be numerous things but might be worth a look.
 
Having had more belts thrown in the past year than most folks will see in there life time, I'll throw in my 2 cents. After checking your pulley alignment, also check that the alternator is square to the crank pulley (part of my cars issue). My small block stroker would toss belts almost every single round of racing. Lots of times I would just remount the belt, other times it would loose it completely or chew it up. I always kept 3 spares in my trunk (no joke)....and some races I needed ALL of them. For my car, the best way to keep the belt on was:

1. Run the belt between 3 points instead of 2 (water pump, balancer, alternator). I was just running a belt from the balancer to the alternator and using an electric water pump, but this made the belt throwing worse.
2. Use the widest, stiffest best you can fit.

The belt that I use now that stays on about 95% of the time, and it is actually wider than the grove on the pulley (it sits a bit out of the groove, but its only 5 bucks from Autozone). I believe the part number is 17465. The 15465 works well too, but I have had better luck with the wider one (17465). I also found a nice thick one at NAPA that worked great, but it was close to 30 bucks.

By the way, my car might be a bit of an extreme example because I race it a LOT...probably 80-90% race, the rest street.
 
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