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Thread: Help! underdrive crank pulley bolt info request

  1. #1

    Default Help! underdrive crank pulley bolt info request

    I've got one of those underdriven crank pulleys made by Unorthodox Racing that I was going to throw on during a timing belt swap. However, it didn't come with the 4 replacement bolts. I've been told on the pointy board that the bolts need to be longer but I don't remember the specs and the pointy board is down.

    Anyone know the specs of the new bolts I need? (size, thread pitch, length, etc.)


    Also, anyone happen to know what size fan belt I need?

  2. #2

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    I have no ideal, does the supplier know, I think I'd go that route.

    http://www.unorthodoxracing.com


    Purdy!

  3. #3

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    The stock bolts are M6x1.00x15. I found that an additional 5mm was all that's necessary.

    By the way, the stock pulley weighed in at 56.4 oz and the UR pulley weighs 14.6 oz.

    The replacement belt sizes that UR lists for the Miata are not all accurate. I used a 880mm belt for the water pump/alternator. My power steering belt was 830mm. This is for a '96 w/o AC.

    Good luck!

    You know not to use these with forced induction, right?
    What's left of a '96 Miata with stock clutch.
    My car exceeds my driving ability. That's the only possible explanation.

  4. #4
    Shallow and Pedantic Majik's Avatar
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    Mark, did you notice a diffrence at all?

  5. #5

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    Quote Originally Posted by Majik
    Mark, did you notice a diffrence at all?
    A little bit, not nearly as dramatic as the lightweight flywheel though. I think UR's horsepower gain claim is a bit high, but then it's really hard to tell anything with the butt-dyno. Overall, I'm happy with it.
    What's left of a '96 Miata with stock clutch.
    My car exceeds my driving ability. That's the only possible explanation.

  6. #6
    Obnoxious at any speed altiain's Avatar
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    Speaking of horsepower... are you going to bring that car out to the ATS dyno day, mark52? I'd be curious to see how it does.
    Iain

    "We don't stop playing because we grow old, we grow old because we stop playing." - George Bernard Shaw

  7. #7

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    The tech guys at Unorthodox are useless. They told me to just use the stock bolts. After I take everything apart, they're clearly too short. I've temporarily used the stock ones, by removing the little plate that goes between bolts and the underdrive crank pulley and using loctite. Hopefully it'll hold for the next few days.

    I did that and a lightweight flywheel at the same time. Definitely a noticeable difference!

  8. #8

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    Quote Originally Posted by altiain
    Speaking of horsepower... are you going to bring that car out to the ATS dyno day, mark52? I'd be curious to see how it does.
    Wish I could, but I'll be moving my daughter back up to OSU that weekend.
    What's left of a '96 Miata with stock clutch.
    My car exceeds my driving ability. That's the only possible explanation.

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