i put this motor together on a stand and got the pullies all lined up as close to perfect as possible.the belt stays on drivin around and revin it, but at around 5grand you can see the belt bow down right under the alt pully.then the more you rev it the more it bows till it just flies off.it,s a 440 with alt,w/pump and crank pully.i cant even make a 1/8 mi. pass. THANKS,AJ

Can you post a pic of the belt setup?

IF you are re-using the belt, toss it and get a new one. It seems once they "twist" and come off, they will do it again! I am sure others here will agree.

Is the alt in the stock location... try to get it closer
and down lower so you can run a shorter belt.. but
your belt is shot... its twisted... also make sure
the alt is square with the crank and pump.. if its
slightly off square it will bend the belt and you will
see it just laying it on a flat surface

Just for the heck of it, get some small angle & recheck all ur grooves for alignment.

Assuming the pulleys are parallel and inline. Run a smooth bolt or piece of tubing outside the long side of the belt. Place it 90* to the belt. When the belt expands it contacts the tube. Stock mid 70's Corvettes had a similar set-up. Notice the tab in upper left corner.
Doug

we make an alternator only serpentine belt kit that eliminates this problem once and for all. we add a spring loaded tensioner into the mix and throwing belts is a thing of the past.

My hemi would throw or break belts until I changed them over to Dayco Top Cog belts. No problems in over 3 years up to 7500 rpms. They run them on Nascar motors. I think you can get them at advance auto. I bought a bunch off Amazon that were extras from a race team and they only cost about $2.99 each plus 1 shipping charge of ten bucks. Cured my problem.

i'll drop some pics in this thread in the morning. or send me an email to jerry@sdconcepts.com

I had this same issue a few years ago when I went to an electric water pump and switched to just having the belt run from the balancer to the alternator...it would throw the belt EVERY SINGLE PASS down the drag strip. I tried aligning pulleys on it for hours...didn't help. When I would race I would have to bring at least 3 extra belts, because sometimes I would be able to retrieve the belt when it flew off, other times it would be gone or destroyed by getting stuck between the balancer and the timing chain cover.

Long story short, I solved the problem by going to a wider and stiffer belt. The belt does not fully sit down in the groove now, but it does not twist and fly off either. If I recall correctly, I had to go with either a 1.0cm or a 1.2cm wide belt to make it work (I started with a 0.8cm wide belt). Good luck.

I've always made my pulleys and made them a bit deeper
so if it stretches it still cant get out of the V
plus I use short belts... its been over 15 years since
I lost a belt

You HAVE to be able to if the alternator is cocked or misalignned

here is the alternator only kit. we are starting to offer billet pulley upgrades as well, and we can anodize the brackets any color you want to match your engine scheme.

i guess I should add that if someone wanted to add other accessories to the kit we could do that as well? say you need a vacuum pump, oil pump or fuel pump, these could all be added onto the belt drive