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Senior Charter Member
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Discussion Starter · #1 ·
I have a V-belt set up on a 402ci engine.

Starts up fine, battery charging well...

When the rad fan kicks on or if I turn it on manually when the car is running, the belt is squealing. I have 10,000 miles on the belt so I will pit a new one in. Is it just loose?

How tight should the belt be?...I may have a little more than an inch of play in the belt...

What else do I look for?

Thanks

Marc
 

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Junior Charter Member
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2,071 Posts
I have a V-belt set up on a 402ci engine.

Starts up fine, battery charging well...

When the rad fan kicks on or if I turn it on manually when the car is running, the belt is squealing. I have 10,000 miles on the belt so I will pit a new one in. Is it just loose?

How tight should the belt be?...I may have a little more than an inch of play in the belt...

What else do I look for?

Thanks

Marc
Marc:

Usually, once a belt starts to squeal, it developes a glaze from the heat and hardening on the pulley surface which pretty much means they become a spare. On "V" belts, I usually like to see no more than a half inch deflection on the longest run to prevent the belt from slipping. Don't overtighten the belt, though as the bearings in the alternator and pump can suffer.

Ron
 

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1,218 Posts
If your alternator has a fan behind pulley, try to spin with pushing on blade as hard as you can with thumb. If it spins under belt it is to loose. An inch deflection on a v-belt it to much.
 

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FFCobra Craftsman
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25,991 Posts
I agree the belt is too loose.When that fan kicks on it is drawing at least 15 amps, and maybe more right at startup, so that is a huge sudden load on the alt.
 

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Cobra Colorist
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5,632 Posts
On a V belt you should pinch with your thumb and forefinger and be able to twist a 1/4 turn. You can try scuffing the sides of the belt with 80 grit to deglaze.
 

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What kind of pulleys?

As V belts age, they get narrower - falling down further into the groove until they bottom out. As pulleys age, they get wider, allowing the belt to slip lower and loosen.

Once the belt is riding in the bottom of the groove, tighten all you want - it cannot develop enough friction.

What the pulleys are made of makes a difference - steel pulleys last hundreds of thousands of miles. Aluminum do not - they can wear in as little as 10,000 miles if they are unhardened billet aluminum.

How much wrap you have on the belt may also be limited using a V belt pulley on a late model 100+ amp alternator. A serpentine could wrap up to 180 degrees, but a V belt pulley arrangement rarely more than 100. You may need to go to dual V belt for enough friction to get a high amp alternator to keep turning. Most of the over the road diesel trucks with 100+ amp alternators use dual V belt or 6+ rib serpentine with more than 90 degrees wrap.

Make sure the new belt fits no more than flush with the top of the pulley, not down in the groove. If it does, one or the other isn't right.
 

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Discussion Starter · #9 ·
Thanks for all the great info...

I'll try changing the belt first...as I recall it seemed flush with the pulley as it is so hopefully pulleys are still good. ...belt could be tighter...I can spin the fins on the alt. pretty easily.

I'll have a look at the double V belt option when I pick up a new belt.

Thanks Again!

Marc
 

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Senior Charter Member
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If you are just running alternator and H20 pump on that belt a single v-belt should be more than adequate. Like I posted earlier you should nut be able to spin alternator by blade under belt. Belt being flush with pulley isn't bad, its when it is below pulley groove is where a problem may result. If you are thinking about changing to dual v, why not just convert to serpentine? They tend not to stretch and you have way more contact surface. Also stay away from any belt dressings or you may as well pick up 2 belts
 

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Discussion Starter · #11 ·
Picked up a new V Belt today. Same NAPA part number as the last one but the measurements are a little different...Not sure why???(13/32 instead of 7/16 width).

So new belt a a little tighter install...see what happens.

Marc
 

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Junior Charter Member
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Belt width

Picked up a new V Belt today. Same NAPA part number as the last one but the measurements are a little different...Not sure why???(13/32 instead of 7/16 width).

So new belt a a little tighter install...see what happens.

Marc
Marc:

That new belt is somewhat narrower than the first one, so make sure it is not bottoming in the groove.

Ron
 
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