My son's BBC Chevelle has developed a habit of tossing the v-belt when he spins it over 6,000 RPM. It is a very basic, stock-style setup circa 1970 - Non-A/C car, has only 2 belts, P/S pump belt stays put just fine, but the Alt/Water Pump belt is the one that he keeps losing when he revs it past 6K. (Normally shifts it at 5800 and belt stays on). He says he has tried running it loose, tight, very tight, no matter. Crank pulley is aftermarket aluminum billet. Stock Water Pump pulley. Alternator has a larger diameter (5"?) Moroso deep groove aluminum pulley on it. I went over and eyeballed it, pulled out a long straightedge, and everything seems to be lined up perfectly, along all 3 "sides" of the belt "triangle". Had him run it, and didn't see any runout or wobble on any of the 3 pulleys. I jokingly told him "just keep it below 5800", which he did not find humorous.
Car never had this problem before, could it be a sign of other troubles? (Damper, crankshaft, bearings in pump or alt, etc)? He said it ruins the belt whenever it gets tossed, they get a permanent kink or bend in them, won't stay on at all after that. Also said he has tried 3 different brands, and even going to a 1.5" shorter length to bring the pulleys closer together.
I don't know what else to advise him, other than put an electric water pump on it...
I still have most all the same parts from my old setup, which I spun to 6800 thousands of times, I guess we could swap things out and see if it cures the issue. What would you change out first? Alt, Bracket, pump pulley, crank pulley, then pump? (Order of easiest to hardest), Or swap out everything all at once?
(Or - ?)

Thanks in advance.

This message has been edited. Last edited by: FootbrakeJim,

Pulley alignment, belt to wide for pulley, alt. mounting brackets not strong enough, non deep grove pulleys are all causes! Also use a smooth belt in the inside of it, no steps.

Years ago NAPA had a premium, I'm thinking deep groove, V-belt you might explore.

I suggest a narrower belt so it fits inside the pulleys ,that's the route I took never lost a belt

Start changing parts one at a time. Start with the oldest first.

Something is ****ed a little. I'd put your old brackets on it and check for cracked/bent brackets.

Mount a camera under the hood to watch the belt and see why/when the belt gets tossed.

My bracketry is all home made. I spin the engine to 7600 and have never lost a v-belt. I also used a straight edge to make sure all the pulleys were square while I was fabricating.

Try a Top Cog Belt. Frequently solves the problem.

It throws belts with the Moroso alternator pulley installed?! Jeez! I would suggest not tightening the belt quite so tight, that might help (oddly enough). I also agree with trying to find a premium quality belt. Once you find one that stays put, buy at least two more of them. Seems like whenever I find one that works, they discontinue it. Take care. Tom Worthington

Went thru this on my small block camaro. I got rid of the aluminum crank pulley and went back to the stock steel one. I used the largest moroso alternator pulley a narrow belt to ride lower in the pulley groove. Then still had to reinforce the alternator brackets because ultimately that was what was flexing ever so slightly, but enough to toss the belt. Like his one time and belt was done.

quote:

Originally posted by SS427IMP:
Try a Top Cog Belt. Frequently solves the problem.

Top cog belt solved tossing the belt on my wifes Nova.

Had a similar problem years ago. BB Mopar stuff. Stock brackets made for a long belt. I noticed the belt had a lot of bounce to it going from wide open to off throttle. Also, the bracket moved/bent very slightly as the rpm went up, I assume as engine speed increases, so does stress on the alternator/bracket assembly. Top Cog belts were better, but still came off on occasion. Ultimately, I made up my own bracketry to shorten belt and make a more stable assembly. No more problems after that.

I'm curious if you could find a place to put a tensioner on it. May allow for less belt movement and keep better contact on pulleys.

This is a really old trick but it normally works. You will need a long bolt and matching nut, you might also have to fab a bracket but I doubt it. Somewhere along the longest span of the belt, see if you can get the long bolt into an accessory hole near the belt. The side of the bolt will be contacting the belt during operation and the nut is to tighten the bolt in place as a locknut. It doesn't have to be touching the belt when idling but it should be within an inch of it. As the engine and belt spins up RPM, the belt will flex and move outward, the long bolt will keep it from going to far and coming off the pulleys. I used to run this setup in our '55 Chevy S/S and my '66 Chevy bracket car. Never lost a belt after putting the bolt in place.

If you're tossing the belt with a deep Moroso pulley you have something flexing. How far is that belt sitting down inside the Moroso pulley?

quote:

Originally posted by Bruce Williams:

quote:

Originally posted by SS427IMP:
Try a Top Cog Belt. Frequently solves the problem.

Top cog belt solved tossing the belt on my wifes Nova.

I decided to change the 10 year old top cog belt on my Vega. I put a (different brand) belt on it. It threw the new belt off on the first run. I put the old Dayco belt back on. It was still on several years later when I sold the car.

quote:

Originally posted by SS427IMP:
Try a Top Cog Belt. Frequently solves the problem.

The Top Cog belt helped me too. I had such a problem for awhile there I actually bent a piece of flat aluminum strap into a hook and mounted it to catch the belt if/when it flew off.

I had the same problem a while back. When I switch to a cog belt, it would break the case of the alternator.

Does the alternator bracket use two long water pump bolts to mount?

I finally figured out that those bolts were flexing, so I made a bracket that allowed me to bolt that the alternator directly to the water pump. Further, I added a tab to the spacer that goes between the alternator and the head to bolt to the back of the alternator. Haven't had any issues since.

I would bet your setup is flexing, can you post some pictures of what your working with?

The threaded rod I used for the pump standoff is grade 5.

Did you add that 4th bolt in there? I think that helps.

The problem with the standouts is that when a long bolt gets hot, it expands more than a shorter bolt and it loosens. This is the same reason why many don't recommend the drive mandrals with the long bolts.

So when it gets hot, the bolts loosen a bit and allow things to rock back and forth. It would flex enough to allow the belt to come off.

Mine would also break those bolts. Bolts provide a clamping for and are not ment to take side to side forces. Just like your wheel studs. What happens when your lugs aren't tight enough, the studs flex back and forth until they break. . If using the long bolts, you need a bracket that mitigates the side to side forces on the bolts. The longer the standout, the force has more leverage to work the bolt back and forth.

Mine started tossing belt recently. I think the bracket may have bent a little or something but it was not perfectly straight. I put one thin washer between one of the brackets to fine tune it and make it perfectly straight. Problem resolved.