2 speed automatic sachs mongoose 29er 47+mph

Discussion in 'Frame Mounted Engines' started by xtsix, Jul 13, 2011.

  1. xtsix

    xtsix New Member

    well i went to walmart and bought a mongoose 29er the othe night, it was a pretty nice bike, full disc brakes, aluminum frame, decent wheels. and took it home, stripped it and took the bandsaw to it:evilgrin: chopped the downtube and flipped it to clear the crank case, and notched it to clear the exhaust. kicked out the head tube 1.5* to give it better high speed handling, and welded it all back together. couldnt find any tanks i liked, so i built my own from an old aluminum road sign, and a filler neck from a 1930s evinrude outboard tank, the engine its self is from a artic cat minibike, its a 47cc 3hp 2 stroke 2 speed automatic, 1st gear is 22.1:1 and second is 11.5:1, with a 12 tooth front sprocket and 26 tooth rear, mounted to the hub with the rotor. im running avid elixer hydro brakes with hayes 203mm rotors,it pulls hard off the line and shifts into second at 23mph, i am hitting 47.6 mph in top gear but im pretty shure with a bit of jetting i can get to 50 all i have left is to finish the tank and mount the new brakes:helmet::devilish:

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    Last edited: Jul 13, 2011

  2. HeadSmess

    HeadSmess Well-Known Member

    thats a nasty gear change!

    like...wow. nasty. be nice to tune that engine in more!

    i want one of those sachs instead of my lousy wankel that doesnt even run :(
    Last edited: Jul 14, 2011
  3. xtsix

    xtsix New Member

    the engines are pretty rare, but they pop up on ebay every once in a while.
  4. Happy Valley

    Happy Valley Active Member

    Where do you live, I want to move next door to you and your tig welder, lol.
    You are one creative little devil aren't you? :devilish: Please ride that thing safely, you are definitely pushing some envelope there. :D
  5. Chalo

    Chalo Member

    Watch out for cracking at the welds

    That frame is probably made from 7005 aluminum alloy, which is used for bikes because it does its own initial heat treatment at air cooling rates, and only needs a simple bake afterwards to yield adequate strength. 6061 alloy, which is more common for structural work other than bikes, must be brought up to almost its melting point and held there for some time, then quenched, then baked at a lower temperature (artificially aged).

    The point is that welding aluminum isn't like welding steel. The as-welded properties of aluminum are a lot weaker than its full strength-- like less than a quarter as strong. And strange things happen at the welds when you mix unrelated alloys, like what's in a typical bike and what's in a typical street sign.

    Keep a close eye on it for signs of cracking, is all, and don't expect it to hold up to the same stress that it would have before you welded it.

  6. Happy Valley

    Happy Valley Active Member

    Yup, all true and good info on what to watch out for on al tubing. The Mongoose Deception is made from 6061 btw...........so I don't mean to be negative OP because maybe you're aware of all this and you obviously got talent, hence my comment about pushing the envelope and riding safe. :D
  7. xtsix

    xtsix New Member

    I annealed The frame before I welded it and stress tested it after re hardening. My tig. Was in the shop so I just used my spool gun. Im not too worried about cracking, the engine is rubber mounted and I reinforced every joint with 1/8 plate. The only thing im worried about are the tires at this kind of speed
  8. Trix

    Trix New Member

    I luv to see a video.....:idea:
  9. 5-7HEAVEN

    5-7HEAVEN Active Member

  10. HeadSmess

    HeadSmess Well-Known Member

    hey! you still have the rear disc on! even with the sprocket....closeup! now!
  11. xtsix

    xtsix New Member

    im running avid juicy 3 calipers, 203mm rotors and a custom built 27 tooth sprocket. stops on a dime and gives change! the only complaint i have is that i really need to balence the wheels, the viberation at 50 is really annoying:cool:

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