Home Forums 2-Cycle Racing Jackshaft considerations for reeds

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    • #17957
      Kasper Kowalski

      I’ve got some TM K11B’s collecting dust since my local track put in a clutched karts only rule :(

      Putting a clutch on them was not an option without putting in a JICA crank half. Then I stumbled upon the jackshaft… all problems potentially solved.

      Though I have some questions on the best way to go about it.

      I normally run 10t front and 80-85t rear. My first thought was put 10t either side of the jackshaft, but this would result in the clutch running at up to 20,000rpm! So I was wondering, should I gear it down to reduce the clutch rpm?

      A lot of people run Yamaha KT100s here, so a clutch to suit one of these would probably be best for replacement parts¬†… most are centrifugal, though there is also the Tomar (have never used such a clutch so no idea if they are suitable for 15000rpm+).

      Anyone have an idea on the best approach for implementing a jackshaft on a high-rpm motor?

    • #17978
      James McMahon

      They put in a ***kin’ what rule!?!

    • #17979
      James McMahon

      OK now that I’ve calmed down. The irony is that with a good clutch setup you wont have to spin those RPM’s on the top, rather you will be slipping the clutch at the bottom end. It might even be worth changing your pipe to suit. It goes against the direct drive mantra, but overall it will be faster.

      Go to the two stroke section on 4cycle.com and ask about jackshafts and clutches. You could probably pickup a suitable combo under the classifieds, used for about $300.

      Nice motor by the way :)

    • #17987
      Walt Gifford

      What you do is gear down the jackshaft and run a 4 stroke type clutch mounted to the jack shaft. Get with the dirt dogs over at bob’s 4 cycle.


      FAA certified jet engine and aircraft technician,
      Nicholson Speedway class champion 2001,
      Yamaha KT100 Service Center,
      41 years karting experience

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