The alt belt blows off everytime I wind up the R's. It's a brand spankin' new belt, and is lined up great. I know I should probably upgrade to a serp system, but the cash isn't there for that rigt now. Any ideas to help keep the belt on the pullies where it belongs??? :-(

Are you sure the tension is correct? You can have them too tight which can cause it to be thrown. Also are you using the correct belt? If it's not fitting into the grove of the pulley correctly that will do it also. A few things to check.

I had a Nova WAY BACK in high school that used to do that. Turned out I had the wrong series belt, example if you are running a 13580 try running a 15580. Increase the first 2 digits of the belt number by 2 and see what happens, you may to get a longer belt also because with the thicker series your gonna lose some adjustment rearward.

Yeah, pretty positive those items are correct. It'll throw the belt around 5500rpm.

Did you always have this problem or did it start after you changed something? Are the belts lined up correctly? A v-belt drive maynot be high tech but there is no reason why you can't keep the belt on at 5500rpm; I have a big block Chevy in my '55 that regularly turns 7500rpm with no thrown belts. By the way it is essential that the belt does't reverse direction once it has been installed and run. If the belt was thrown off and you reused it but installed it so it's turning in the reverse direction that could be a problem. I always install new belts so that whatever wording/numbers on the belt is facing the front of the vehicle so I can reinstall the belts the same way.

I had this problem on my 71 w/a 350, could not figure out the problem. My husband finally figured out that the lower alternator mount that comes off of the water pump has slightly over sized holes in it, so by holding up on the alternator while tightening these two bolts first then the through bolt to the head eliminated throwing belts. Not holding it up let the alternator drop just enough to put the pulley out of line and throw the belt when revving the engine.
Hope this helps.
PS, this is a chrome aftermarket mount (MR Gasket I think)

align the pulleys

As far as I can tell by looking straight down the pullies, they are aligned. My PS pully is bent and wobbles noticably and that belt stays put :?

Many, many years ago, I owned a car that regularly threw belts. Never did find out why, but did find a fix. I put wire centered belts on that sucker and never threw another one.

Ok man let me share my experiences with you. On my 78 elco i would either toss or snap the belts everytime i got on it.... i mean 5200 rpm and the lights dimmed out and i would get a thrashing sound under the hood. I tried every freaking belt that auto zone, pep boys and o'reilly's sales. It got to the point where I would just carry 3 spares with me at all times lol. I can change a belt in about 4 minutes.

I checked belt alignment.... I tried new pulley's.... I took it to dif people for them to look at... you named it and I tried it.

Okay so no more suspense... what was the prob you ask? The stupid alternator mounting bracket. It was 20 years old and it would flex and allow the alternator to hop when the strain got on it. I went to the dealer and bought the chrome version. It is twice as thick and twice as strong... prob cost me $20 and i can't toss a belt to save my butt.

I have fixed this same prob on two other small blocks and both of them had the same prob and both of them fixed with replacing the stupid bracket lol!

Take care...

Morris

Good tip. Thanks.

Great info guys, thanks!!!!