This was one of those projects I couldn't get out of my head. I had seen, on the internet and in person, the small 2-stroke engine powered scooters which were becoming increasingly popular. Naturally I wanted one, but I'm not the type that would just buy a commercially available scooter that will work well and last for years and be happy about it: I would have to build my own.

This was also a project that kept changing. The initial design worked, but not very well (or for very long.) I kept redesigning as I went along, tweaking the bike for more reliable use. In its current condition it is quite effective at moving someone around and makes for a quick and easy to build project. My initial build lasted about 8 hours over one day. When I hopped on the thing and went flying down the road at speed, I was very thrilled and surprised to have gotten that much of a result out of one day of bodging. While you view this project, please keep in mind that some major improvements could be made to my design to fix various safety and performance issues. If you plan on building a similar design, make sure check out the lessons learned step before you build.

For more info about this project and a bunch of others, check out my website: thewidgetforge.com

Step 1: Design

First, a quick disclaimer about the design: Since there is a lot of variation between different bikes and small engines, this design will likely need to be adapted to fit your equipment. It's important to figure out what you have before you commit to an engine or bike since some types won't work very well.

The design was constrained most by the motors available to me at the time and my lack of welding capabilities. I wanted to use my all-terrain style 12 inch tire scooter along with a clutch but I couldn't come up with the necessary equipment. My searches of local (and on trip that was not so local) yard sales and eBay returned few useful motors. Mounting the motor without welding also posed a challenge since that was the efficient and obvious way to fix everything together.

When I couldn't get a motor with a clutch, I got frustrated enough to haul off and improvise a spindle driven design for my bike from 5th grade. The bike is quite small for me, but still allows pedal starts and has coaster brakes which frees the handle bars for the gas and kill switch. I decided to make it front wheel drive for ease of construction: there's a lot more free room up front.

For the engine, I used a small 26cc McCullough engine which came from a hand-held leaf-blower. It is a half shaft motor (only one side of the crankshaft is supported) without a clutch, but it had a threaded shaft which allowed for easy attachment of the spindle so I was happy.

I initially went very simple with the design: just make some brackets and bolt it on. That worked for a few miles when the engine mounts loosened up and the spindle stopped transferring power. I eventually modified the bike to include a spring tensioning system to keep the motor firmly on the tire.
<p>I made a bet with a mate, who could make the fastest motor powered bicycle by the end of the year. I'm losing at the moment, with him having completed his build using a chainsaw motor and with me having not started yet, but i think i think i can leave him in the dust (literally) with this build. Thank you so much man, you have blown new life into a bet i would have lost and given me a fighting chance. now all i need to do is find a bike, motor, assorted bolts, nuts, springs and god knows what else, but at least i have a reference. thanks again bro, heaps of respect.</p>
<p>cool, are you still alive?</p>
<p>Yes... it isn't that dangerous ;)</p>
<p>Well where's the fun in that then!!?</p>
<p>good if you only make right turns</p>
<p>BTW it look unsafe because the blower is on one side and it will be heavy on the left so you will fall just saying because I just saw the picture.</p>
I made few of them using weed wacker engine way back 1996, mounted on the rear using a converted bike rear rack hinging the engine so you can have a clutch. I used hard small diameter skateboard wheel as a driver on the shaft. We mounted them on our mountain bikes and had lots of fun.
I think you did great ! Ya lots of bugs to work out when building like this. <br>But, man that is half the fun. I would try mounting on the rear of the bike. <br>Most engines run the same direction. That is why mini bikes use a jackshaft <br>to run the chain on the other side. As a rear mount, do a jack shaft or make a lever <br>to pull the engine off the tire. The spring to keep tension is a must. <br>If useing a jackshaft, you could use the rear gears. But, I'm sure that will <br>open a hole mew set of bugs to work out. lol <br> <br>All in all, Great job....
You said you hit 29mph? My pedal bike speedometer says I've gone 168 km/h...No joke! I didn't do anything at all. Its set for the correct size tire and everything...I know when it happened, but I didn't think I was going that fast...That was a bigger hill then I expected! If you don't believe me look at the photos!
I think what the bottom number is, is <em>the total</em> distance you have travelled.<br/>I may be wrong, but that is how mine used to work.<br/>
Ya cause my max speed is 0! WTF! no the odometer reads 600km. The top number is always the speed you are currently traveling. the bottom number is whatever the letters next to it say. If you look it says Mx for max. and if you press the button again it goes to Average which is 20km/h then it changes to calories and so on. That is the actual Max. speed!
So what you're saying is that on a mountain bike you have gone faster than world record holders:<br> Sam Whittingham 2009 133.28 km/h (83 mph) Flat surface, unpaced, (recumbent) and<br> Markus St&ouml;ckl &nbsp; &nbsp; &nbsp;2011 164.95 km/h (102.50 mph) Downhill on a volcano, on a serial production bicycle.*<br> <br> I agree that your speedo shows a max of 168.4, but I'd say it wasn't reading right. Still, I'm open to being wrong - you should perhaps look at having a go at the world record particularly for &quot;downhill on a volcano, unpaced, serial production, upright&quot;.&nbsp;<br> <br> *For other speeds see:&nbsp;<a href="http://en.wikipedia.org/wiki/Cycling_records" rel="nofollow">http://en.wikipedia.org/wiki/Cycling_records</a>&nbsp;
Guess so! Haha! I don't think it was reading properly. I know that I have hit 100km/h on that bike, downhill, as it is calibrated properly for tire size and it is fairly accurate, but something must have gone wrong to get 168km/h. That and I have hit 170km/h on my motorbike, and I can tell that I have not hit that on a pedal bike. If my some amazing chance I have and didn't notice/realize, I hope I could figure out how to do it again! Wouldn't mind holding a world record really...
I'd say re-calibrate that sucker!
Never had to, after seeing that I got a friend on my bike (motorcycle) to ride next to me at 10, 20 and 30 km/h to see if she was off, was dead on. I think what it is, since it works off a magnet on the rim that goes past a reed switch or coil of wire on the forks, my best guess is at high speed there isn't enough time between one pass of the magnet and the next and the computer goes nuts and gives you monstrously high value for speed.
I believe you. I've hit 45 MPH on a mountain bike when i was 13 years old. Could've gone faster, but the hill was really windy.
i notice from your pics that you didn't reattatch the pull starter. To start it you just pedal until the engine turns over?
Yeah, no pull starter. A few quick pedals and the motor starts and at about 12mph I stop pedaling and let the motor take over.
will it go up hill
no, once the engine tilts above three degr- YES IT GOES UP HILLS YOU TARD ITS AN ENGINE NOT LARGE ROCK
<em>buffersam says: Nov 28, 2010. 12:00 PMReply Bwah Ha Ha Ha Ha - still laughing after reading this post - love the &quot;YOU TARD&quot; reference............... :D </em><br> Yeah me too! :] &nbsp; I especially like the way you interrupted yourself at &quot;degr-&quot;. You are one funny guy!!<br> With due respect to dragonsniper, of course, the engine may not have been powerful enough to pull uphill...
Bwah Ha Ha Ha Ha - still laughing after reading this post - love the &quot;YOU TARD&quot; reference............... :D
Yes, you do need more to do, ha ha. It's a legitimate question. There are no shiftable gears and the engine used to move air, not a person. <br>Anyways, in step 7 he says it will and you can always help it out by pedaling. <br><br>Nice instructable Jnkyrdguy! I have been wanting to do this for years now, but my designs always involved attaching something to the spokes and using a belt or chain drive which is more difficult. This seems like a good solution.
I think he means how much horse power.
Did you have trouble getting the spindle centered? i stuck a peg on with a washer inside the peg as well and it is about estimated 1mm off center. i started it without putting it on the bike and it vibrated like crazy.
I got lucky! The spindle I used had the same threads as the shaft on the motor so it's just bolted on. Otherwise, I'm not sure how I would have attached it without welding or somesuch.
I got the metal peg on but it was too big (1.25) and had no torque so i finally ended up using this pvc pipe. i also stuck a bearing in the far end of the pipe and attached it from the side opposite of the engine. Haven't gotten a throttle to stay attached though :(
Forgot the Pics :o
I hope to make something along the lines of thsi if i have any questions could i email you? if you want check out my blog at www.projectpai.blogspot.com
You can PM me on here if you have a question and I'll try my best!
cool thx <br>
do you think its possible with the housing still on<br>
ya, i see that your mount is burnt
I made it just about the same way as you, except for instead of brackets i used zipties andl screw locks(not sure if thats the name), but my spindle keeps slipping on the tire. Please help.
I had the same problem with mine until I added the spring to hold the spindle down to the tire. Otherwise the brackets would loosen up and the spindle would loose grip over time. If you already tried a spring, maybe changing its position or adding a heavier spring could help
I meant do all gas motors spin in the same direction because i dont know which side to mount the motor on
does the gas motor always spin in the same direction?
when the engine is on idle doesn't it still spin? because if you want to stop you have to shut it off!
Yes, you have to shut it off to stop! It's not convenient, but it works
well thanks for replying!
Very cool, I wonder if this would work slightly better with a smoother road tire versus a knobby tire? Once you buy yourself a welder, you will truly free up your future builds. You can pick up 110 stick welders on sale for less then 59$ and wire-feed welders for under 100$ Go for the wire-feed, sure everyone will say to buy the full MIG kit, but if your starting out flux-wire is still awesome. Later if you want to go full MIG, you will still have a nice portable welder that works well even in high wind. Often place like harbor freight in the States or Princess auto in Canada will also put on the the auto darkening helmets for 40$ at the same time the wire-feed welders go on sale, usually 4 times a year. Enough prattle about welders though, great build!
It would work a lot better with smooth road tires! The knobby tires mean lots of vibration and worse contact with the spindle, but that's all I had available at the time... If I ever get back into this sort of thing I'll definitely have to grab a welder.. thanks for the tips!
would this thing go a mile with some pedal help
I've gone about three miles on an 8th tank of gas, so you could get a lot farther than a mile if you fill her up.
have you done any tests regarding the fuel economy of this build?
I haven't done any careful tests, but it could probably do more than 80 mpg pretty easily based on my above comment. I think the tank is about a quart in total volume.
What with the engine stops at top speed you flying foword!
Could you put this motor on the back of a mountain bike?

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