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Discussion Starter · #1 ·
69 chevelle 1970 396. tosses belts every time I floor it.
the crank pulley has a slight wobble. things ive added to help the belt stay on.

new harmonic balancer
new crank and water pump pulleys
new 5 inch deep groove summit alternator pulley
5 new different sized belts
new bbc alternator brackets
a flat serpentine style idler pulley in between the crank and alt.
the bottom pulley still has a wobble, the crank is not bent cause ive had 2 balancers and 2 different pulleys on it and it acts the same. I look at the balancer as its running and its dead strait. the alt is on the passenger side I don't know if that matters or not. does any one have an idea what the eff is going on? ive shimmed the alt out and in a billion times and ive seen no difference. is there somewhere I can get a v belt tensioner pulley? if I t went to a serp setup do I need a new alt and water pump? a 1970 motor shouldn't be this hard to race
 

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"the crank is not bent cause ive had 2 balancers and 2 different pulleys on it and it acts the same"-Huh? Still trying to figure that one out...

What is your tension of that alternator belt? Can you twist the belt after its all tightened up?
 

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Did you buy a new belt after it tossed it? Once a belt gets thrown off it will not stay on ever again. At least that's been my experience.


Ok just saw you have had 5 new belts....
 

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The very best alternator pulley you can use is the deep groove GM unit used on corvettes, in conjunction with that heavy duty OEM alternator fan.

Of course, things have to be lined up, but since I found one, I have not thrown belt.
 

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Discussion Starter · #6 ·
I have used new belts after ive tossed them ive also went back and picked them up off the road, either way they get thrown off as soon I a race the car on the street. I could drive half throttle all day its when I smash it they come flying out the hole in my hood
 

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Mine used to do the same thing, mine also has ac and power steering, used diesel grade belts ( I think) or at least top quality belts, solid "V" and no "cogs" on the "V", top cog OK, and I also use the short power steering belt, (from crank to power steering, not crank to water pump to power steering) and have not thrown one in over 2 years at 7000 rpm, stock pulleys. This is also with the ac belt removed for track use, I think it's just to long for 7000rpm!!!
I also run a 7 blade 10,000 rpm capable flexalite flex fan.
 

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If I can remember I will look tomorrow when I get home and get some numbers, they are either gates or dayco, does yours have power steering? I got them at local parts store.
 

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crank pulley wobble, could it be bottoming out against balancer bolt washer, or balancer itself?
 

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Dave , mine are not diesel grade, those are on another vehicle, dayco gold lable IIRC, my chevelle alt belt is dayco top cog 15456, I know you posted that you have used them, mine have been on there almost 2 years, over 150 passes at 65-7000 rpm and appx 3500 hiway miles, stock pulleys from a 1981 big block 1 ton chevy. Hope you get it figured out:thumbsup:
 

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This is how I solved throwing my belt...

I just solved this issue on my big block. It was throwing the belt at the track. I switched to pulleys that use a ribbed flat belt around the crank, water pump, and alternator. The power steering still uses a V belt. Worked great. The pulleys are from a late 80's 454 truck, such as an 87 v20 Suburban. Here's the part numbers I used...

Powermaster 114 serpentine pulley for the alternator - $23 new at Summit/Jegs/etc
ACDelco 14087537 crank pulley - $47 new at Amazon
GM 14087536 water pump pulley - I bought used on Ebay for $48. Discontinued from GM.
Dayco 5060460 or equivalent belt (46" 6 groove) $15
Reuse your power steering belt

I plan to have them chromed over the winter to make em purdy. :thumbsup:

 

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Sounds to me like the snout end of the crank - where the balancer mounts is slightly bent.

When you have the pulleys and balancer off the car, crank it over and see if it's bent. I bet it is and that really sucks.
 
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