machining help for a homemade chainsaw bike!

[milkcratemotorer]

hello everybody! built prototype number one and trying to address some of the shortcomings with a new build. the motors im using are tonka chainsaw motors, 33cc i think, i got four of them, so trying to make them work for not too much money. the setup now is direct drive with a bmx peg, no clutch. want to be able to turn the motor off and pedal relativly normally at a moments notice, (as to not draw attention to myself if certain public servents drive by). anyways, had two ideas to maybe make this work, but dont know if there even possible. the first is to use the clutch the saw already has (its one where the chain drive is on the inside) by taking the drum to the local machien shop, having them grind, or remove the chainsaw sproket, and attach one that i bought. this would require keeping some of the metal from the original sproket and boring the new sproket to match, since there is a beiring in there the clutch drum rides on. the other idea i had was to by a short shaft that is the same diameter of a gocart clutch, and have the machine shop bore a hole in the shaft with reverse threads (to match the shaft of the chainsaw)esentially making an adapter. the chain would drive a roller, not like the current stanton drives

heres a picture of my first build, only got about 15 miles on it, worked pretty good, except for no clutch, got up to almost 30 mph with just a little peddling, but would pretty much hold that speed. the nut holding the peg came loose, since its a standard thread reverse nut instead of the metric one that i think i need, altho i could be wrong about that too, do chainsaws have some kind of special thread pitch?

 

[milkcratemotorer]

after looking at my thread, looks like i really didnt ask a question! I guess im just asking someone that has experience machining stuff if these ideas are in the relm of a machine shop doing the work for a reasonable price (say under 50 bucks). I know ive brought automotive cylinder heads to automotive machine shops and am usually surprised at the quaility of work they do for not too much money, but thats about as far as my machining experience goes.

 

[professor]

Don't know about the machining, can you just get a sprocket that fits on the side of the clutch orig. sprocket and weld it on? Gotta keep it straight though.
That sprocket needs to go to an intermediate shaft (a jackshaft) to gear down a lot more before going to the back wheel. Think about a ratio around twenty to one to start with. Each set of sprocket's ratios are multiplied by the ones that follow.
So, a 5:1 goes to 4:1 giving 20 to one overall.

 

[milkcratemotorer]

theres not really room unless the original sprocket was machined down. the gearing will be close to one to one, got the figures on a scrap pies of paper, but going to use a 2 1/8 inch roller to get the rpms down a little bit, like a 10 tooth drive and 15ish load sproket

 

[loquin]

2-1/8 inch???

Chain saw engines rev very fast...

But, even if it were the same as a TLE43 2-stroke mitsubishi (which tops out in the 8000 RPM range from the factory) ...

8000 RPM and a 2-1/8 inch roller equals 50+ MPH.

 

[milkcratemotorer]

yeah, but its going to have a geard reducion, the bearings im using are only rated for 5,000 rpm, so using a larger roller to get the speed down, even tho it will still probly be spinning a little faster than 5,000

 

[loquin]

5000 RPM, 2.125 roller, and you're looking at a max speed of almost 32 mph.