Belt size for underdrive pulleys with air pump

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Mar 18, 2007 | 07:41 PM

moconnor

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Belt size for underdrive pulleys with air pump

I found lots of threads on belt sizes and a nice guide at http://www.banzai-racing.com/ that lists belt sizes for many pulley combinations.

However, I could not find a belt size for underdrive alternator and waterpump pulleys with an Unorthodox main pulley AND the stock air pump pulley. (The alternator and waterpump pulleys are from RX7Store, but I think that - with the exception of Unorthodox, which uses stock sizes - all aftermarket pulleys are pretty close in size here.)

Mar 18, 2007 | 08:10 PM

Larz

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If all else fails route string like you would the belt, tie it off and take it to an autoparts store. Get a few different belts and return the ones you don't use.

Mar 19, 2007 | 10:42 AM

moconnor

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Quote:

Originally Posted by Larz

If all else fails route string like you would the belt, tie it off and take it to an autoparts store. Get a few different belts and return the ones you don't use.

I was hoping to avoid the dozey guys at the local parts counters.

Mar 19, 2007 | 10:46 AM

Mahjik

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Just use a string/twine to trace the route of the belt then measure the length of the string. Once you have the length you need, you can see what you can find in whatever available ribs.

Mar 19, 2007 | 10:59 AM

Wargasm

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I agree with the other posters. Set the alternator to the maximum, then measure with string.. then set to the minimum and measure with string again. Get something in the middle of that range with the correct number of ribs (5 I think??).

*edit* My car uses ONE belt around the alternator/WP/eccentric. Obviously if you are trying to replace a belt that doesn't touch the alternator, you dont' need to mess with that bit! *edit*

I couldn't find a 5 rib belt in the right size for my car, so I bought a Goodyear Gatorback belt with 1 extra rib and very carefully cut one rib off with scissors. Been fine for about 3 years

Sep 18, 2008 | 10:31 PM

primerGrey

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moconner, what size belt did you end up using?

Sep 18, 2008 | 10:47 PM

moconnor

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I posted this in a thread a few months ago that got a huge amount of interest.

https://www.rx7club.com/showthread.p...ulley+air+pump

Quote:

Belt size with Unorthodox main pulley, Greddy WP and ALT pulleys, and air pump

I did lots of searching for this belt size but found nothing beyond "get some string, measure, and then go to Pep Boys". Even Banzia Racing's belt guide did not have this combination listed.

It took a few trips back and forth, but eventually I found that the 1385mm (54.5") belt did the trick. The Goodyear Gatorback part number is 5PK1385 (or 4050545). This is a 5-rib belt.

I also found that the 1000mm belt recommended by Banzai for the Unorthodox main and stock AC and PS pulleys would not fit and I needed a 1015mm belt (6PK1015, 4060400). This is a 6-rib belt. I had the idler pulley to the maximum open position too. Not sure what other peoples experiences are here.

FYI, the RX7 Store and cheapo eBay WP and ALT pulleys are the same size as the Greddys.