Briggs and Stratton Bike - Motorized Bicycle

stewart · #1 07-21-2008, 07:18 PM

I have included a picture of the motor bicycle that I built using an old ten speed road bike. The front mount engine required no modification to the existing frame, just a new fork. All the parts from this are common hardware or off of a go-kart. It handles real well and is geared for a speed of 35mph. It could easily go faster, I just didn't trust riding that fast to work every day...it was scary enough blowing a tire at 30mph. The height of the handlebars is comfortable and I dont smell the exhaust when I ride. Any comments or questions welcome.

UncleKudzu · #2 07-21-2008, 08:17 PM

now that's a different approach! nice looking work, too. is that a 20" front wheel?

there was a very early motorcycle that had a front wheel arrangement like that; wish i could remember the name of it.

**Ilikeabikea** · #3 07-21-2008, 08:50 PM

Welcome to the forum. I've never seen a motorized bicycle set up like that before. I bet that will get up and go if you really wanted it to. Glad you joined us..........................

**Dave31** · #4 07-21-2008, 09:36 PM

Welcome to the forum

Nice work

deacon · #5 07-21-2008, 10:09 PM

Now that's a bike. Welcome to the madness.

that's what I want to do next on a much smaller scale of course.

seabillco · #6 07-22-2008, 08:55 AM

7-21-08
Hi, Stewart
That looks great! Very Nice Work!!!
May I ask, how did you attach the drive pulley to the front wheel?
Also, I think that's a BS 3.5HP engine, right? Do you know how much it weighs?
I'm using a Ryobi 31cc 2 stroke and it weighs 3.75 pounds with no fuel.
Finally, I'm guessing there's a centrifugal clutch on the crank end, right? Are you happy with that approach? That would be a very nice feature for stop and go stuff...
That is one of the coolest looking builds I've ever seen. If you have any more pictures, videos, etc. I'd sure love to see them.

Thanks for sharing!
Steve G.
Grants Pass, Oregon

Spunout · #7 07-22-2008, 11:44 AM

that certainly is a unique take.
may i ask why, you opted for front-mounting?

stewart · #8 07-22-2008, 04:52 PM

Yes the front wheel is a 20" wheel that is normally used on carts. I used this type for the stronger spokes over a bicycle wheel. I opted for a smaller radius wheel because it let me get away with a single stage reduction off the engine crankshaft. The bearings were welded shut and welded to the axle to create a live axle. From there I welded a go-kart sprocket to a universial hub to drive the axle. The sproket is pretty close, but not perfect since I didn't have the hub turned to match the id of the sproket.

The engine is quite heavy, probabally 20-25lbs. It has a beefy flywheel and has i think 160cc of displacement. The clutch is a centrifugal clutch straight off of a go kart and works great. Since I have the bike geared for a modest 35mph, with a 3.5hp I hardly even have to pedal before the engine works. For stop and go the clutch works, but will wear rather quickly because unless the engine as at high rpm the pads slip and wear. It is excellent however because I can idle the engine at stop lights just like a car.

I went for the front mount for a couple of reasons. First, I had to do no welding or any modifications to my bike frame. Secondly, I needed a strong place to mount the engine. The geometry of the existing frame made it difficult to mount such a heavy motor because the frame only has one layer of tubes running lengthwise. The fork I built has 2 layers, which ensures the motor doesn't twist at high throttle. I hope that makes sense, if not I can try to explain more.

I sure I could gear this motor to go crazy fast, but geared it low to keep my crusing speed near the legal limit of 30mph with the engine at full rpms. Crusing with the motor at too low rpms for a long time would fry my clutch. When on a level surface at 35mph my throttle is hardly even open

mgladden2 · #9 09-09-2008, 02:43 PM

am i the only one who shook his head and laughed when he saw this? both at the ingenuity, and the downright madness of motorized bicyclists.

Jemma Hawtrey · #10 09-09-2008, 02:50 PM

I remember when I was a kid my father used to have an evil petrol mower with an engine that was the very devil to start... but once it got going..

Imagine my amazement when I see on youtube a bike with a similar design to yours running the identical engine as that battered and recalcitrant lawnmower.

In the case of that bike the builder had put in layshafts to take the drive but it brought back alot of memories.

I like the chain drive idea.. but that engine is pretty substantial. I do know of one front fork design with twin cylinders and the roller drive between them, but I dont think more than one survives..

Jemma xx