I just recently put a high dollar ( to me anyway) supercharged 355 in my 68 Malibu. It has all of the stock pulleys that the original 307 with PS and AC came with. Every time I twist the motor over 6000 rpm it throws off the belts. Yesterday it took out the blower belt and trashed the idler in the process, a $240 expense not to mention the embarrasement and headache! I know deep groove alternator pulleys are available but what about water pump, power steering pump,a/c compressor and crankshaft pulleys? I've used new belts and everything looks in alignment but this is still happening. Any ideas? Thanks, Bob

Trash those pulleys and get a set of pulleys from March Performance! Your belt throwing problem WILL BE SOLVED!

Does March carry all of the pulleys I listed?

Bob,
We fought this problem on my son's car and decided to change all the pulleys. Rather than go to the expense of changing all 3 at once we started with the alternator first. Just changing the alternator pulley cured the problem. We have tried, very hard, to throw the belt, and it just WILL NOT come off! This is a deep groove pulley and the part number is 3829387 from GM and it's about $21 (if you can get a discount at your Chev parts dept). We also did not have to go to a longer belt.

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I had the same problem with my 454 tried aftermarket alt pulley and it helped alot but anything above 6800rpm I sill would throw a belt finally went to a march crank pulley as well .... problem gone I'll twist it up to 7500rpm+ now with no problem except for the large grin on my face but as long as my big block holds together I'll be ok good luck.....Manuel

they've got everything you need Bob!

Bob,

I had this problem also. My alternator belt would fly off around 4500 rpm. I fixed the problem by putting the shortest possible belt on. Now I carry it to 6000 rpm without any problems at all. I hope this helps.

Get rid of those cheap belts that have those treads on them and get some belts from GM. Their made by Gates. Also try some deep groove pulleys.

Mark

Dayco "top cog" work good too, there notched on the outside and solid on the inside. did the that swap on a couple of cars and have'nt thrown one since.

Are the puleys new?
Is there paint in the grooves where the belts ride??
sound crazy?
Check the pulleys, if there is paint in the grooves, clean it off all of them, or drive a little easier until the belt wears off the paint in the groove. If the belts are straight and tightened properly when the pulleys shine where the belts ride, they will no longer throw.

Sean

Those Dayco Top Cog belts are the ones that my car would throw off at 5,000 rpm. I replaced them with some thick solid Texaco belts and the problem went away. The Moroso or GM alt. pulley will also help a lot.

Thanks for all of the advice. I've used NAPA and Gates belts and it throws 'em all. I think I may initally change the crankshaft pulleys first since all three belts come off.