How to Build a cheap friction drive bike

My engine came today, and even thought the ebay seller is a liar of monumental proportions, I was ready for him sorta. It took four hours but I got the engine through phase one. Rryobi 31cc engine instructions.

I am not going into all I had to do to make the engine run. Lets hope you score one that is already running. So lets begin at that point.

If it is on a trimmer you need to deconstruct it.
This is the first step.
1. Remove the steel shaft leading to the line feed head. Usually there are four screws holding it on. Just take them out and it should come right off.

2. With that removed, you will see a silver bell shaped piece. That is the outside cover of the centrifugal clutch. At the end of that hollow tube is a screw which holds the bell onto the drive shaft. To remove it you need to block the drive mechanism of the engine. To do that remove the spark plug and stuff a rope into the spark plug hole. Be sure to leave some of the rope sticking out so that you can remove it.

use a flat blade screw drive that will fit into the hollow tube to remove the screw. It should be easy enough to remove. Since you have blocked the engines ability to turn over it should work no problem.

3. Now that the bell is gone you should see the real clutch parts. There are a couple of springs. If you remove them the clutch will fall apart. When it does it leaves a jam nut with what looks like wings. Just take a vise grip and unscrew it. Now you have the first phase done.

This is how your engine should look at this point. The bolt I added it is a 3/8" fine thead cruiser axle bolt. YOU can use a bmx axle peg (not mountain bike) as a drive wheel. I am going to use something different and that bolt will hold it on (I hope)

No clutch for the build. This will be another of the most basic builds. After I test ride it if the the motor does okay, I'm going to install a big gas tank of some kind. I learned on that small engine that running out of gas is a no no for soooooo many reasons.


As for the distance, I will go down now and try to get you a measurement. 2 7/16 definitely less than 2.5 inches.

On the carburetor is the top line the one that goes to the tank or is it the one that goes to bulb. I might have them setup backward. Which might account for my gas leak. The more I think about it the more I am leaning that way.

ps I went and checked I'm pretty sure I had them backwards. Now tomorrow when it dries out I can put in some more gas and start it again. Then continue the build.

Now back to de-constructing the engine.

Then next thing after you are sure your engine starts and runs. You need to strip the rest of the case away.


you want to remove those five bolts but save them you will use them again.


This is pretty much what you have at this point.


More to follow tomorrow. I have to wait for expoxy to dry..

Well on mine if you hook the lines up backwards the gas just runs out the bottom. I think I have it figured out now the intake is the bottom inlet and the return is the top one. At least that is the way the gas doesn't pour out and it does run.

I always let my jb cure over night if I can. It seems to work better and be stronger that way. It dries to the touch in a couple of hours but I don't trust it.

I'm still debating that 2x2 frame for the engine. Another reason I didn't rush into it. Now that the pull chord is off, I will have to wrap a string around the drive wheel to start it by hand. I might not even bother, just go right for the drag start.

Norman will the extra 6cc make any difference in the engine performance.

Building the motor mount.

I decided just for fun to use a 2x2 as part of the motor mount. If it tests out alright I will probably use more wood in the build. There are several parts of this mount frame I could easily replace with wood.

anyway photo one shows the kind of hinge, the 2x2 and a shelf bracket they are all part of the mounting hardware.

The next image shows mending strips of steel from home depot. Since I don't cut and weld I had to buy all these metal parts. Some I had to adjust and some the bolt holes lined up pretty well.


Its mostly trial and error but what you need to do is to mount the hinge either to a shelf bracket or a mending strip and shelf bracket depends on what you need to do to make it work.



Now you can test fit it to the bike. The shelf bracket gone on at this time as well. It is to tie a box configuration together.



The next thing to do is tie in the existing throttle cable and wire a kill switch. that's next time.

If there are any questions please ask it will help me explain this more fully.

another view.


The tension is supplied by an old fender brace attached to the non motor side of the frame. It also helps keep the motor straight (I hope)

I lifted it wrapped a cord around the drive wheel and pulled it. I dont build these anymore

I dont buld these anymore but I lifted them from the wheel and used a rope around the drive wheel usually to start them

A couple of pieces of angle iron to hold the motor..... Some nuts and bolts..... A henge.....a spring....Something to use as a drive wheel.....

That should get you started...

In my case i took it off and mounted to the drive shaft the ryobi it will just screw on. Some of the others have a different size shaft.