Friction Drives

My goal is to build a bike system so simple any idiot can build it.
Very low maintenance.
I want to use an engine that you can buy locally for under a hundred bucks
if it brakes pack it off to a lawnmower shop to have it repaired.

In other words a cheap motorized bike for the masses.

It doesn't have to be perfect, just serviceable. Okay you have to pedal it some uphill, but you can ride it five miles without being worn out when you get there. You don't have to be a mechanic to enjoy motorbiking with the system I want to build.

The Henry Ford of motor bikes....
 
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well the brand new 31cc engine worked out real good then fell apart lol. I finally got to real ride it today. The suicide clutch didn't work all that well, so I added a cable after the first attempt and it worked much better.

Then one of the attachment points on the motor broke from stress. I had no idea I had that much stress on it. It was a case of stupidity on my part .

But the good news is the 31cc is almost ideal for a friction drive bike. There was no hill on my test track that it wouldn't pull by itself. It actually did better than the 33cc chainsaw for some reason. Not nearly as much skipping over the tire just more pulling.

I think if I can get it remounted without the stress and get everything double bolted and use locktite on the top nut it will work much better. All in all I like the size of the engine. Not sure I like it all that well but then again it seems to work just fine the two times I got everything working at the same time.

I can not drag start the engine so I use a rope on the drive wheel. The trimmer I bought did not have a clutch so the gravity clutch works just fine. The centrifugal clutch looks awfully light weight to hold a drive wheel. But who knows. Anyway I think I can have this bike running in a couple of more days puttering.

For some reason at the end it wouldn't take gas on accelleration. I have to figure that out once I get it mounted again. No sense worrying about that till the engine is mounted correctly.
 
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A couple of things worth noting about weed whacker and friction drive.

Of the five or six weed eater type engine I tore down all of them could be torn down to a threaded drive shaft. The ryobi 31s I tore down had 3/8 fine threads. The bolens 31cc I just finished a craftsman 25 I used before it locked up on me have 5/16 fine threads.

Now how about drive wheels for these things. I have just figured out a new non welding required drive wheel. Go to your local hardware store. Buy a galvanized pipe cap for a buck. Get any size that will fit on your flywheel. I got a 3/4 inch one. The outside diameter of the cap looks as though it will fit on the flywheel.

Now my drill is broken and I'm waiting for a new one. When it arrives I will drill a hole in the end cap. The end cap is pretty shallow so I can bolt it onto the flywheel very easily. then I will use a couple of vise grips to tighten down a 4" pipe nipple into the end cap. A 3/4 inch pipe is just a hair over an inch outside diameter. That should be enough. I will take a file and rough it up before I screw it into the end cap.

So now here is the nity and the gritty of the bike as I see it now.

If you buy a bolens weed whacker from lowes it is 75 bucks with tax. You can use the motor as your power source

The lever can be used for the gravity clutch.

A bike brake handles and cables can be used as throttle and a second one for the gravity clutch. Since mine came off junk bikes I can give you a dollar figure maybe ten bucks.

The drive wheel was two plumbing fixtures as listed above two bucks. You need a piece of angle brace from the home improvement store. A henge and L bracket as well. Also a stout spring.

I think you can put the motor on the bike for about a hundred bucks. From the little bit I did ride the 31cc before it shook itself apart, that was an out of balance drive wheel by the way, it seems to be the ideal size friction engine.

My plan was to build a bike that I could ride on errands and for some exercise that a senior could afford to build and ride with just a little pedaling. I wanted all the parts to be easily available to anyone and inexpensive. I wanted the owner of the bike to be able to take the engine off and drive it to a lawn mower shop for repair or if it was old enough, just to toss it and bolt on a new one.

I think I am there now. I need to wait for the drill, put on the drive wheel and go for it.
 
Deacon,
You mention easy build and affordable. I built my bike with an old weed eater I found in a trash pile and angle iron from a bed frame. Just one piece of iron holds it on the bike. BTW the bike was one someone was throwing away. I mounted a bmx peg on the motor for a friction drive. All I have in my motorized bike is $7 so far(fuel lines and spark plug). Although I plan changing some throttle cables later. I will post pics this weekend of the build. Alltogether I think it took three or four hours to build. You can see it here YouTube - Motorized Mountain Bike
 
Here are the pictures of my friction drive. I think this one is as simple as it can get. No welding, just bold it up and go. What do you think?
 

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I like it and I have a few questions.

1. What size engine.
2. How good is it on hills.
3, Do you drag start it.
5. does it have a throttle. I have been debating if I want a throttle on my 25cc or not. I don't remember the last one being of much use since I ran it wide open all the time anyway getting it up for the next hill. The brakes seemed to work pretty good as a throttle.


I can hook up a 25cc solid like that but a 31cc I had to set so I could lift it to rope start.

I like to think of the 25cc that shuts down when it comes to a stop sign as a pure assist engine which is great. I am going to build another one of those to ride around getting some exercise.

The 31cc seems to pull the hills better but requires a lift mechanism to keep it from spinning on the tire.

The 33 chain saw engine I tried a few weeks ago did the same thing. I had to lift it to start it with it's reel starter, then lower it onto the wheel.

I am experimenting with a used tire cut and jb welded to the drive wheel. If that works it will solve a lot of our problems., It will get much better traction than the smooth metal wheels and it should not wear out like the heater hose some of us tried. As soon as the roads dry I'll give that a good work out.
 
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1. The engine is somewhere between 21 and 25cc. It came off a weed eater xt200 (really old).
2. I'm in Florida so no hills, other than really small ones. I does ok if I have the speed up before reaching them.
3. I took the rope start off so the only way to start is drag starting. I thought about a lever to raise and lower but I opted for it directly on the tire.
4. I move the back brakes to the left hand side and ran a cable from the right hand brake lever to the throttle.

I have a ryobi engine on the way. I hope to have alot more power from it than the weedeater. So far the smooth friction drive hasn't given me any problem other than slipping when wet. I have some epoxy and sand to put on the shaft but havent got around to it yet.
 
"RJ" said:
1. The engine is somewhere between 21 and 25cc. It came off a weed eater xt200 (really old).
2. I'm in Florida so no hills, other than really small ones. I does ok if I have the speed up before reaching them.
3. I took the rope start off so the only way to start is drag starting. I thought about a lever to raise and lower but I opted for it directly on the tire.
4. I move the back brakes to the left hand side and ran a cable from the right hand brake lever to the throttle.

I have a ryobi engine on the way. I hope to have alot more power from it than the weedeater. So far the smooth friction drive hasn't given me any problem other than slipping when wet. I have some epoxy and sand to put on the shaft but havent got around to it yet.
Click to expand...


Did you have to do any work on the flywheel to get it to attach. It looks like you are running the same peg as me, and I had to do a lil grinding to get it to fit correctly.
 
I had to grind some as well, but now I have a way to attach a home made wheel that is much easier. I don't have a grinder so I had to use a file to do it. Lost of work and in the end I didn't even use it.

I get a pipe nipple. 3" will do I have 4".. You then buy an end cap. Drill a hole in the end cap and bolt it onto the drive shaft. Then to change the wheel you just twist it into the end cap. You can have a second wheel ready to go on if the one wears down.

I attached a piece of tire to the drive wheel with jb weld. I ran it all day today and the epoxy held fine. What happened was where the tire had been worn out it went right down to the case. I cut it off and attached a bit of a better tire and I also put it on so it turned differently. The high and low parts of the tire come in contract with the wheel. I just did it so tomorrow I will give it a try.

The epoxy and sand worked okay for me but the tire rubbed it off in pretty short order. Some guys swear by it so maybe I did it wrong.

When you get the ryobi you might not be able to drag start it. If not you can use a rope on the drive wheel. It's how I start my 31cc engine. I finally rode mine today. It did real well but I still don't have the tension on the drive wheel right. I like having the clutch on a brake lever but I think it might need to be adjusted so that the suicide handle is the real clutch not sure just yet though. I don't seem to have enough tension on the wheel, but I'm going to wait for the next tire drive before adjusting anything again.
 
I just finished reading the 8 pages of this thread and it's great. I wanted to mention for Decon and others here a couple things I picked up on.

On the fuel line sizes, yes there is a smaller diameter and larger. The hardware store I shop sells it off a big roll they have hanging up. The small size one goes in the smaller size hole and the larger through hole made for it. It's a tight fit so it will seal the gasoline inside the tank. If the small is used in the large hole, you'll know right away. That little filter that's on the end of the fuel intake line is quite important. I've seen them break off the hose right where the nipple inserts into the hose. Then it's just a mater of time till the bottom of the carb getts full of dirt and quits running. Ya just gotta pull it all down, blow it out, and I use carb cleaner with the thin red tube that inserts into the spray can nozzle to blast it all out and blow back thru everything. They usually fire up after theat.

Another FIX for seized motors, if you haven't heard of it, is an old lubricant product called "Marvel Mistery Oil". It's red and looks something like auto transmission fluid. But the stuff is a one of a kind in it's ability to free siezed
pistons etc. I've seen people run lawn mowers out of crank case oil and lock the things up. If you can get there about as soon as it happens.......pull the spark plug and pour an ounce or so down the bore so it soaks on the ring overnight. Prop the mower or engine up so the piston faces up over night.
By the next day you may have to gently tug some on the recoil rope start but the engine should bump free. Pull the engine thru a few times to spread the Marvel oil thru the bore and then refill the motor with oil. When starting it, run it at low speeds for the first hour or two so it will be about like breaking it in again. But you can save an engine this way if you can get on it in time.
This oil can be used in a 4 cycle crank case or the fuel tank. I've used a little
of it in 2 cycle mix. It is a good upper cylinder lube.

I used to work with an older guy who had used the stuff all his life. He would
pour a quart in with a fresh oil change when he was ready to pull an engine to rebuild it. After driving the engine for a month or so he'd pull the oil drain and
drain the motor before pulling it out of the car. The insides would be super clean where the Marvel oil soaked all the crud loose. (the oil pan was usually full of crud that had broken off in clumps)

These friction drives are really growing on me for their simplicity of fabrication, inespensive easily available motors & parts, potential gas millage, and still maintaining the pedal drive. It still has a bicycle nature about it which would
appeal to the "Green" spirit of young people and the grocery getter for seniors
where the general public and Law Enforcement agencies would have to even concede the economic necessity of these times driving seniors to this form of conveyance for their daily errands. :ride:
 
I figured out the hard way about the gas lines but I found an easier way to do it for me at least. I just bought a handful of those vacuum connectors and I have them on all my friction engines. I can use the 1/8" line in the tank with a fuel filter on one and none on the other. I can then just connect them up the fuel lines that were on the engine to begin with. It seems to work without starving anything. It allows me to switch gas tanks anytime I want without having to cutting the filter off then reinstalling it.

The first thing i do from now on after I make sure it runs is to switch to a larger see through fuel tank. The one I seized taught me a lesson. Check it before each ride.

And the reasons you gave are my reasons for investing the time and money in getting this right. So far my favorite is the 25cc helper motor. The person using it needs to know nothing about maintenance. If they can mix the oil they are good to go. Just pedal it off and the engine starts up. Put on the brakes and it shuts down.

It also doesn't need springs or any kind of clutch. The engine is cheap enough so that if you screw it up, you can take it to a shop or get a new one. Also the mount is easy to do.

I am designing mine for the guy with very few tools and no real skills. In other words I'm designing it for me.

With the price of gasoline being what it is, one tank of an suv will pay for a motor from your lawn mower repair shop. One more will pay for a junker bike and the hardware to mount it.

On the next one I build will be a 25cc. For ease of use I'm going to try it with no throttle adjustment. Just wide open throttle or engine dead from trying to pull the brakes. The 31cc will slip on the tire at throttle up but the 25 will choke down. It should be a little ladies best friend. Pedal it up to speed and let the motor take over. Want to go a little faster pedal it to raise the speed then the engine will maintain it for you. At least that is how I remember the last one i built.

The chain saw may be the most powerful and useful to me personally, but the 25cc helper might be the easiest one for most people to use. Even easier than the bike bug.

Now that I have an easy inexpensive drive wheel I should be good to go.
 
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Yea, I had got lucky my cousin had a Dremel and that made everything so much easier.
Now i just have to work out my tension issue. I have been trying to readjust it to keep from using the rubber hose. Overheated on me just a bit ago after a 3 mile ride. So I am gonna reduce the tension tomorrow.
 
You might have too much tension on the drive. I like mine to skip just a little when it is under stress like up hill.. It is hard to get the tension right for sure.
 
Yea, It had been parked for a couple days and I changed my fuel mixture (leaned it out a bit) and it was running rich and bogging pretty badly, so before I left I adjusted my needle, It actually started revving good and getting some power before he started getting hot. So tomorrow, my focus is to work out the tension issue and then readjust my needle.
 
Unsolved Rubix,
I had to grind down a little. Dremel worked great on the motor. I finally ended up grinding the bmx peg and it seems to work better. On the engine there were four places where it would not fit, I ground flat spots on the peg. Then it slipped right in. As for tension I just guessed. I mounted it on the bike with the air out of the tire and then inflated it. Seemed to be right I havent adjusted it or anything.
 
Yea, yesterday I put some ribs in the peg to reduce some of the slippage I had. Just the 15 or so we put on there made a huge difference, this is all staying back till I get some JB Weld and then I am gonna do some experiments with that and see what I can whip up.

Right now I am runing probly about 1/8th an inch of pressure which how it is acting is too much, So I am gonna see how much more I can reduce it.
 
How did you put ribs in it? I thought about welding some on. Or just welding splatter. I have some epoxy and sand but havent tried it yet. Can you post some pics?
 
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