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  1. #1
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    S-Works Crankset Hirth Extension

    Like a few others out there I have an S-Works carbon crankset that won't work in our existing BB68/73 frames and looking for an extension piece. Saw a few posts including the one with proof it is possible but I had already contacted a machine shop that does Hirth work regularly to see what was possible.

    $170 for a single 20mm extension to let me use the road cranks in my BB73 frame but the price comes down to $75/each if I order 10. Told me the length can be customized for each one at no extra charge so checking to see if there was enough interest to spin up an order. Also checking with Mattias to see where he is at in the process as I don't want to take any business from him.

  2. #2
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    A 32mm extension would be nice to fit a fat bike.

  3. #3
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    I would buy one for $75.
    I hope we can get a few more people interested.

  4. #4
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    We are off to a good start, only been a day and have several nibbles... I will probably get 2 so I can use it in either a 68 or 73 mm shell with external cups so only need 7 more.

  5. #5
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    Perhaps this thread could be of help...?

    Tuning guarnitura Sworks per telao SCOTT PF29

  6. #6
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    Mattias was looking at doing these for much less than $75.00. I had emailed him requesting one, but never heard back from him - this is going back at least 1 year ago. I never found another source.

  7. #7
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    You will also need to source / manf a new bolt, the existing one is not long enough for anything more than a few mm spacer.

  8. #8
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    It is always cheaper if you can find a fellow hobbyist with the right equipment to do the task so if he is capable then I will gladly give him my money too. I have a friend with a small CNC machine I am trying to see if he can make the part but for now the real machine shop is my best source. They have to make a profit so I don't begrudge them the cost even though I am still trying to reduce the per unit price...

  9. #9
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    I'm interested in 1, or perhaps even 2. Probably just very short ones (like 3mm) to allow mtn cranks on 73mm BSA.
    This hasn't been done very often before, though I guess Lightning does it on all their mtn cranks - does anyone have any concerns that a slight inaccuracy in the machining would lead to a more sizeable misalignment of the cranks and therefore bearing drag or creaking?

  10. #10
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    Not sure how short it can be made but I will check with the machinist to see if there is a limit.

    I am sure if the machining were inaccurate it would cause a problem but the shop I am dealing with does some very high tolerance work so this is pretty easy for them.

  11. #11
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    Thanks NITF.
    BTW, can anyone confirm whether the road and mtn cranks are identical aside from the spindle length? So a road crank spaced to have the same axle length as a mtn crank (with a longer hirth extension) would have the same spider position (ie chain line) and Q-factor...?

  12. #12
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    I would buy one too

  13. #13
    L3X
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    I would buy one it this allows me to run a Specialized crank on my 68mm threaded SL3 $75 seems fair too.

  14. #14
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    That is what I want to do with mine so that is the plan. Looks like there is enough interest so I will start moving forward with the machine shop, once I get things finalized I will get confirmations and preferably deposits from those that are ordering one.

  15. #15
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    Making the bolt is not easy - I made one for a 26mm extension a few years ago. I have been waiting for Mattias to make the spacer for me ever since. It has a strange fine pitch thread and you need some way to make the allen key hole. I had to form the hexagonal hole so I could only make the screw out of aluminium - which may not hold up (needs testing). as such I think the bolt alone will cost you at least $50


    S-Works Crankset Hirth Extension-photo-16-06-2013-18-16-47.jpgS-Works Crankset Hirth Extension-photo-16-06-2013-18-19-19.jpg

  16. #16
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    I would be interested in one that would allow the MTB crank to work on a 73mm shell. I'm a bit worried about the bolt though, as mentioned.

  17. #17
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    Looking into the bolt now. It is an M12x1.0 bolt. It is not very common but still a standard thread so there might be a chance. I will check with the same machine shop and see how much it would add to make a matched set with the spacer and the bolt. Will post back as soon as I get some more information.

  18. #18
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    Hi NITF,

    I'm interested in getting one for $75.
    As for the 73mm BB shell, I thought Niner Air9 RDO frames have 73mm shells and have seen Specialized MTN cranks mounted on that frame.
    I'm interested in placing my cranks on a Scott Pro HT frame (92mm) BB.

    Dave

  19. #19
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    Quick update...

    The machine shop can make the bolt as well but have gotten busy at the end of the year so I will post more after the holidays. I was able to negotiate a lower price on the extension but by adding the bolt into the order it will probably go back to the original price of $75 including a matching extension and bolt set.

  20. #20
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    Hey NITF,

    I'm definitely in for one of them.
    Thanks for looking into it for us S-Works crank owners.

    Dave

  21. #21
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    Quote Originally Posted by NITF View Post
    Quick update...

    The machine shop can make the bolt as well but have gotten busy at the end of the year so I will post more after the holidays. I was able to negotiate a lower price on the extension but by adding the bolt into the order it will probably go back to the original price of $75 including a matching extension and bolt set.

    can you do a 5mm extension with matching bolt like on the italian weight weenies
    link above?

  22. #22
    Cassoulet forever !
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    Would be interested in a 5.8mm extension + bolt like on the italian forum
    Frenchspeaking 29"ers community site http://VingtNeuf.org

  23. #23
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    What width space would be needed to put road cranks on a standard bb30 frame?

  24. #24
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    Precisely none

    They are BB30 spaced.

  25. #25
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    Yes, but the Q is far too narrow for an MTB. I guess you could space it to clear the stays and then add equal spacers outside the bearings.

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