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Old 12-29-2008, 09:09 AM
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Serpentine pulley measuring/isntalling

Got my 383 in my '70 Nova this past weekend, and am on the last few steps to getting it started up. I have a march performance electric water pump pulley set, with only the alternator running off the crank right now. (no power steering, with an electric water pump, of course.) I measured with a spare wire the length of which was needed to go around the pulley from the crank to the alternator, and came up with roughly 44 inches. That is with no tension. How do I go about selecting the right length of belt? Do I subtract a certain amount of inches from the outer diameter I measured to provide a certain amount of tension? Google searches have yielded nothing, as well as forums searching. Thanks for any help.

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Old 12-29-2008, 10:46 AM
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Belt tension is provided by either an adjustable mount on the accessory or a belt tensioner. In the case of factory serpentine belts, there is a spring-loaded pulley that provides the tension. In the case of V-belts, you loosen the alternator mount bolts, install the belt, then pull or pry out on the alternator and retighten the bolts.

But, if the alternator is in a fixed mount, you can't do it. Even if you could find the perfect length of belt (which might be 43.7754") there is no way you could install it. You must have some way of adding tension to the belt after its installed.
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Old 12-29-2008, 10:54 AM
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I have an adjustable eyelet bolt that has threaded eyelet bolts on both ends so I can adjust the slack and tighten down to get the tension just right. Here is a link to what my exact setup looks like with an image:

http://static.summitracing.com/globa...ch-22005_w.jpg

The part that is adjustable is the bottom portion that is bolted to the alternator. Since the optimum length (measured via some extra wire) is roughly 44 inches, is it safe to say I could go with around 42 inches and adjust the tension from there? How much tension is enough/too little? Thanks!
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Old 12-29-2008, 11:14 AM
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Ok, I see...

Proper tension is when you can twist the belt 90* without too much trouble. Grab it in the middle with your thumb and first finger and twist it. If you can twist it 90* (so that its straight up and down) and then it gets harder to twist it more, you have it right. Basically, let the alternator be your guide for tension. As long as its not slipping or being thrown off, there is enough tension. If you do the twist test and you can't easily twist it 90*, its too tight and you risk accelerating wear on the alternator bearings.

What I do is adjust the alternator the whole way in. Then I measure using a seamstress' tape or a wire like you did. I buy two belts; one that is that length, and one that is a half inch longer. Install the belt, then you have the maximum amount of adjustability to add the tension you need. I buy two belts because none are exactly the same and getting it home only to find its too tight to slide on is just frustrating
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Old 12-29-2008, 11:18 AM
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Thanks curtis73, will most likely be doing this tonight!
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