Idler pulleys question

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potshotscott

Registered User
Well the old girl is 25 years old and needs new idler pulleys. They're shot and I'd like new ones. Here's the thing. I've read most of the threads in the forums and seem to believe that all three pulleys should be 76mm. I have two 76mm pulleys and one that is 70mm. The 70mm pulley is on the idler next to the AC pump (SC loop). I'm starting to think I have a larger than stock SC pulley. I see a lot of threads talk about pulley percentages but have found one thread here that might suggest that 89-93 model SC pulleys are larger. Is this true? The second post in thread below might suggest why I have a 70mm pulley on the SC belt loop

http://www.sccoa.com/forums/showthread.php?64213-Early-model-SC-pulley-on-a-94&highlight=sc+pulley
 
Yes, early SC pulleys are a different size and can bump later model's boost.

When juggling SC pulleys, I've found you can juggle belts or juggle idler pulleys to make up the difference. Also depends if the jackshaft pulley is a different size too.

Keep tabs on the tensioner range gauges to judge when to replace belts, other than if they look sad, of course.
 
potshotscott said:
Well the old girl is 25 years old and needs new idler pulleys. They're shot and I'd like new ones. Here's the thing. I've read most of the threads in the forums and seem to believe that all three pulleys should be 76mm. I have two 76mm pulleys and one that is 70mm. The 70mm pulley is on the idler next to the AC pump (SC loop). I'm starting to think I have a larger than stock SC pulley. I see a lot of threads talk about pulley percentages but have found one thread here that might suggest that 89-93 model SC pulleys are larger. Is this true? The second post in thread below might suggest why I have a 70mm pulley on the SC belt loop

http://www.sccoa.com/forums/showthread.php?64213-Early-model-SC-pulley-on-a-94&highlight=sc+pulley
Click to expand...

Sounds like you have a 2 part question.

First part on the tensioner pulleys you are describing, they are factory sized - 2 are 76mm and 1 is 70mm ... they offer both sized pulleys on Rockauto.com and the 70mm is even referenced to the A/C - https://www.rockauto.com/en/catalog...ged,1140578,belt+drive,tensioner+pulley,10346

Second part - the SC pulley as mention by KMT is smaller on the 89-93 M90s. I want to say the difference in pulley size is equal to a 2-3% OD over the 94/95 pulley. It's not a vast difference but it is there.

Hope that helps.

-Tim
 
Thanks Tim - the main reason I asked the question is I received my order from Rockauto that was based solely on year and engine in the car (not sizes) and I received the wrong parts. 2 90mm pulleys and a 76mm ribbed pulley. Bummed. They were legit Motorcraft parts too. The search continues. Great to get a conformation that the supercharger pulley has been hopped up.
 
I currently run a 7% SC pulley.

My idlers at this time are 70mm & 76mm (Dayco 231016 all metal). I'd think with just a change to an early SC pulley the stock belt would still fit. I elected to swap mine out to keep the tensioner in range and be able to install it.

I have also run a 5% jackshaft AI pulley, but not for the last 2 years. Running 13# as it is, even w/better exhaust.
 
Thread update. The Gates 38023 pulley (found at O'Reilly's) is doing the deed for me. Ordered two of them and ended up finding a solution at "gates dot com". They're search engine (by attribute) is a little clunky but does work.
 
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