Motorized Bicycle

[JB Weld]

Starting a new project. Decided that a motorized bicycle would be a good idea. I told the father in law about my plans to use a chainsaw engine (gotta love strokers!) and he said he had some laying around. Got to his house one day to go deer hunting and he had a couple old McColluch Timber Bears sitting on his tailgate. After talking to him a bit about the missing parts we looked through his shed and found a couple more. I really thought the Timber Bears were the ticket as there were two, but shitty recoil and weak spark was uninspiring. So, decided to dump some premix into a newer, smaller, 38 cc machine and it fired right up!

Sold the other saws for almost nothing, and bought a carb kit for the little 38cc. Will post updates.

[sav0r]

Make sure whatever bicycle frame you use has beefy rear dropouts. I live on a street with prominent bike lanes. I am about 2/3's of the way up the hill before getting to a large park that a lot of people like to bike to. Anyways, a guy absolutely ate shit right in front of my house on his motorized bicycle. The chain side dropout failed and supporting the rear wheel with one dropout didn't work out too well. The thing is, he was going like 30mph when it happened, and being on a bicycle instead of a motorcycle he only had a helmet on. The meat crayon was real.

It sounds like a fun project though!

[JB Weld]

I'll keep that in mind. I have an old old Haro mountain bike that a neighbor left to the curb. It was either this or a freestyle 20" bike that was also left to the curb.

Had some time to work on the project today. Disassembled the mountain bike cranks. Then removed the tiny rear sprocket from the 20" bike and decided this will be the engine sprocket as it has 10 teeth.

The sprocket has a recess on the face that will be away from the clutch, so filled the recess with weld. I have to bore the center out to 14mm to accept the pilot bearing from the clutch. I tried to drill it out on my drill press and just created smoke. Must be hardened, so I'll take it to work and see if someone in the machine shop can give it some attention. I will remove the original chainsaw chain drive from the clutch and weld the 10 tooth to it.

Also started making a 48 tooth rear sprocket out of a table saw blade. I'll find a way to attach to the free wheel.

[m in sc]

i love the idea of a motorized bike but id def take it too far and die.

I do have a really old 3hp allen bradley tractor, continental 'super 3' rope pull motor i want to stuff into a retro mini bike frame though. or make a battery charger out of. haven't decided yet.

def beef up the axle and dropouts & bearings.

[1976RD400C]

The neighbor kids and I made a couple of them when we in our early teens. 20" inch bike with 2-3hp Briggs motors. I don't remember how we mounted the big sprocket to the rear wheel but it didn't free wheel. No clutch, the engine sprocket was keyed right on the motor so it was direct drive.  Push it and it would start and then let it stall to stop. We got two off them running and terrorized the neighborhood until the cops put a stop to it. I'm surprised but no one ever crashed one. Then we upgraded to Rupps. 

[JB Weld]

Progress pictures. Walbro carb needed cleaning and rebuild. Also removed the chain lube pump(seen as empty space behind flywheel) and cleaned all the sawdust and wood out of the plastic housing.

[JB Weld]

Adding a small 10 tooth sprocket from a 20" freestyle bike. Had to open up the center to 14 mm to make room for the clutch bearing. I think the hole tightened up on the clutch drum after welding, as the bearing was/is a bit tight. Going to run the bike like this a while and fix if necessary.

[JB Weld]

Rear sprocket made from a table saw blade. Modded the cassette to carry the sprocket and retain free-wheel function as well as right hand drive.

[JB Weld]

A bit more progress today. Attached derailer parts to the frame to change the chain direction. I was going to add sprockets to the crank, but decided to try this first. Started the engine mount, so far only have the engine strapped to it for looks.

[AtLarge]

 

[85RZwade]

I love the ingenuity of this project. I was pondering the direction change of the chain... if you put your powerplant above the rear wheel and behind the seat,
1) chain run is direct
2) center of gravity is better for wheelies
3) the whirling chains of death are no longer under yer balls
Just an idea

[Djg8493]

I agree, this is a fun project!
anyone interested in in this check out the site gasbike.net
I accidentally went down a wormhole on these when I almost bought a bicycle engine for my GT80, I got the picture and was like, what in the heck is this.  Turns out they make full kits on this site and one of them is called the GT80 (still a 80cc 2 stroke)

[JB Weld]

I love the ingenuity of this project. I was pondering the direction change of the chain... if you put your powerplant above the rear wheel and behind the seat,
1) chain run is direct
2) center of gravity is better for wheelies
3) the whirling chains of death are no longer under yer balls
Just an idea

You're suggestions are valid!!

I've seen this done a few different ways on youtube, and many mount above the rear wheel and don't want to do that  😉.

Not sure if this little homeowner saw will make wheelie power with my 250 lbs anyway. And yeah, really afraid of the death chain lacerating my femoral, but have 450k+ in life insurance so at least my wife will be taken care of for a while.

Seriously not sure if this will work well yet, but excited to try. And I prefer chain drive as opposed to some of the friction drives that I've seen. Next time I may splurge for a sprocket conversion which mounts a sprocket on the left of the wheel and do a jack shaft with direct drive instead of a clutch. This way I can peddle start it. I think motorized bicycles are legal in WI if they retain pedals.