First Build: Full Suspension Mongoose Friction Drive

[Need For Steve]

I've been a long-time lurker here on the forum, and I've finally whipped myself into the mood to start my own build! I have a basic plan, a bike, and an engine. The plan is to ultimately end up with a somewhat-decently functioning friction drive setup, and to use a bit less gas on trips that aren't time-dependent.

The bike is a Mongoose 26" DXR AL mountain bike. It's an 18-speed bike with a fairly decent suspension setup, and side-pull brakes. I'm not sure of the age, maybe 4-5 years? It doesn't need much to get going and I'm getting a good price on it.

It needs a rear inner-tube and possibly a new set of tires, as the ones on it show a bit of dry rot.

The motor is a Homelite SX-135 25cc weed eater motor, dated 08/95. Fuel lines and a new primer bulb will have it in good shape, then it's onto figuring out how to mount a peg. The real bear, I'm thinking, is going to be in figuring out a mounting system that'll work with the rear suspended fork. My first real idea is a sleeve mount on the bottom of the seat tube, with the motor held down onto the tire by spring tension.

I've got a bit to figure out, but it should be a nice little rig if I can do it right. I've even got my first real piece figured out; a thumb throttle that lived on my old MTB as a thumb shifter...

 

[curtisfox]

Take a look at this mount...............Curt

http://motorbicycling.com/showthread.php?t=50647

 

[Need For Steve]

Thanks Curtis, I hadn't come across that post in my searches yet. It looks a lot like what I'd initially planned, but the rear fork on the bike looks like this...

Not much room for a latitudinal clamp. I'm thinking I may use a similar hinge setup, but clamped onto the rear seat post, that way even with the movement of the suspension, spring tension from springs mounted to the rear axle could help hold the tire down. I'm gonna have to get creative somehow...

 

[curtisfox]

I built a sub frome and welded it to the suspension frame,just used some old stay tube for it. If you PM me you email i can send you a picture...............Curt

 

[Need For Steve]

Curtis, thanks a bunch for that picture! It's given me a bit of an idea for a bolt-up mount, as I don't have access to a welder.

I picked up some threaded rod today at Lowe's, and an working on pulling the Homelite apart now...

 

[Need For Steve]

Got the square keyhole shaft off to find a nice threaded crank. Now to find a drive peg or socket...

 

[curtisfox]

Curtis, thanks a bunch for that picture! It's given me a bit of an idea for a bolt-up mount, as I don't have access to a welder.

I picked up some threaded rod today at Lowe's, and an working on pulling the Homelite apart now...

Welcome you could post it if you want,I would have if i new how.............Curt

 

[Need For Steve]

Engine work and Frame Mounting starts Monday!

 

[Need For Steve]

Progress!

The mounting frame for the engine is done!

Drive peg is a 7/8" deep-well socket, 1.25" outer diameter.
Frame is made out of 1/8" weld steel.
No welding, everything will be bolted.

The threaded rod at the seatpost mount is 1/2", the rod bracing the frame is 3/8". The seatpost mount is temporary; I didn't have enough weld steel left to make a couple solid plates for the U-bolts so I'm using the janky plates that came with them to hold the bar on for mock-up. Just have to brace the frame to the bike frame for side-to-side movement, and then...

Throttle linkage!

 

[Need For Steve]

Here's a picture of the mount on the bike...

 

[wheelbender6]

I like your dual triangle shaped swing arms for mounting the engine. Some kits and home builts use a single piece of steel or aluminum for a swing arm with mixed results. Are you going to install a lift clutch (engine lift mechanism)?

 

[Need For Steve]

I'm not gonna use a lift clutch right away, though I'm sure it'd be quite possible with this frame. I'm just gonna pedal to start it, I figure a few calories burned starting it up won't hurt

It initially was only gonna be the engine-side triangle, but I very quickly found that this just wasn't strong enough, being mounted from the seat post. The second triangle tying it all together keeps the engine side from bending or twisting. I still have to run some braces from the seat post mount to either side of the bike frame to prevent twisting, but other than that, the mount should perform well as pictured. The roller is kept on the tire by spring tension.