2 speed automatic sachs mongoose 29er 47+mph

xtsix

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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:devilish: 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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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 :(
 
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the engines are pretty rare, but they pop up on ebay every once in a while.
 
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
 
Watch out for cracking at the welds

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:devilish: 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,

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.

Chalo
 
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

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