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  1. #1
    Wrench Savant balindamood's Avatar
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    Retapping French threaded cranks

    Has anyone ever tried re-tapping french pedal threaded cranks to english (using actual taps, not pedals)? This may have been covered, but search does not work well on my Blackberry.

    Thanks
    "Where you come from is gone;
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    Senior Member Capecodder's Avatar
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    The French threads are 14 X 1.25mm and can be retapped using a 9/16" X 20tpi tap with no issue.
    Amy, I'll always remember you...... I miss you so much, for you filled my days with so much joy.

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    Yes, it's pretty straight forward. You'll want to use sharp taps, not ones that have been used to chase threads for years. Most important part is to go in square or you'll end up with a wobbly feeling pedal. Check it with a good square on all sides as you start, having the arm clamped to a flat surface will help as well.

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    no one cares -holiday76's Avatar
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    Just did this 45 minutes ago. Use oil, it's easy. Be careful to get the tap in straight. I did it on stronglight 93's.
    Mmmm, bicycles.

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    Senior Member Grand Bois's Avatar
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    You just missed a discussion:

    http://www.bikeforums.net/showthread...Threaded-Crank

    Someone has retapped French cranks using pedals?

  6. #6
    Knotty Guy Anthropy's Avatar
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    Regular threads are not intended to cut material, so I do not believe that un-modified threads would stand a chance. It is possible to take a hack saw and file to the pedal threads and modify them. Take a look at a self tapping screw to see what needs to be done. However, it would be a large pain in the butt and much easier to simply buy the taps. You could also explore sending them off to have them done (local bike shop?)

    Tom

  7. #7
    Senior Member randyjawa's Avatar
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    Someone has retapped French cranks using pedals?
    In a pinch, you can use a hard bolt, by comparison, to chase, not cut, threads in a softer metal.

    Take and old left pedal and an old right pedal, ones that you will not use again. Using a very find blade hacksaw, cut a slot or two or three equal distance from each other. The slots run parallel to the center line of the bolt.

    Now, using lots of lubricant, thread the correct pedal spindle into the correct crank arm. In a wee bit, back out to clear the groove, and in a wee bit more.

    That's how one chases threads when there is no proper thread chaser, or tap(s) to be had.
    Learn how to find, restore and maintain vintage road bicycles at... MY "TEN SPEEDS"

  8. #8
    Senior Member Capecodder's Avatar
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    ^^^^^ This is old school for sure.... Being an automotive technician by trade, I've done this many times in the past 35 years when at a loss for a needed tap, and it works. I do however suggest a practice run on something other than your cranks before diving in to your beloved crank using this method. This is how us old guys did things back in the day......
    Amy, I'll always remember you...... I miss you so much, for you filled my days with so much joy.

  9. #9
    Senior Member Grand Bois's Avatar
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    You won't find a bolt with the correct 9/16" X 20 threads. You'll only find bolts with 9/16' X 18 threads. Pedal threads have a unique pitch, so what are you talking about?

  10. #10
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Grand Bois View Post
    You won't find a bolt with the correct 9/16" X 20 threads. You'll only find bolts with 9/16' X 18 threads. Pedal threads have a unique pitch, so what are you talking about?
    Perhaps a sacrificial spindle from another pedal?

  11. #11
    Senior Member Capecodder's Avatar
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    You use a pair of old pedals as the self made tap..... Everyone has a pair of junk pedals lying around.

    Quote Originally Posted by Grand Bois View Post
    You won't find a bolt with the correct 9/16" X 20 threads. You'll only find bolts with 9/16' X 18 threads. Pedal threads have a unique pitch, so what are you talking about?
    Amy, I'll always remember you...... I miss you so much, for you filled my days with so much joy.

  12. #12
    Senior Member Grand Bois's Avatar
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    Using pedal taps is the only correct way to do it. They're not that expensive and you can help out your friends. I've tapped more of other people's cranks than my own.

  13. #13
    Wrench Savant balindamood's Avatar
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    Have taps
    Have cutting oil (aluminum even)
    Have machinist square
    Have vice with leather jaw covers
    Have Stronglight cranks with french threads
    Have a white Ford Econoline Van name "Vincent" (van go...spelled per my 4-year-old)
    DO NOT have french threadded pedals I care to use on the Mercian build

    One of these things in not important
    "Where you come from is gone;
    where you are headed weren't never there;
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    Senior Member Grand Bois's Avatar
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    I don't think you could get the tap started crooked even if you tried really hard. It threads right in and just removes a little bit of material. Fourteen millimeters and 9/16" are very close. You don't need special cutting oil for this. Any oil will do. In fact, no oil at all will do.

  15. #15
    rhm
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    multimodal commuter rhm's Avatar
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    [QUOTE=Grand Bois;12258007Any oil will do. In fact, no oil at all will do.[/QUOTE]
    True, dish soap will do. That said, use oil.

  16. #16
    Senior Member randyjawa's Avatar
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    Perhaps a sacrificial spindle from another pedal?
    Two sacrificial spindles, one right hand thread and one left, right? And that is exactly what I meant, except in industry, I rarely had to chase the threads on a bicycle pedal.
    Learn how to find, restore and maintain vintage road bicycles at... MY "TEN SPEEDS"

  17. #17
    十人十色 Dawes-man's Avatar
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    Quote Originally Posted by Grand Bois View Post
    I don't think you could get the tap started crooked even if you tried really hard. It threads right in and just removes a little bit of material. Fourteen millimeters and 9/16" are very close. You don't need special cutting oil for this. Any oil will do. In fact, no oil at all will do.
    I'm afraid you're wrong there, old boy. I managed to do exactly that on a 1950s NOS Stronglight 49D. The crank side worked fine. I still regret it. The local engineering shop says they can repair it for $60 but I'm hesitating...
    "I bet you'd do the same if they was you." F. Zappa

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