Friction Drives

I rode the chainsaw bike about four miles today. I am going to have a learning curve just like for the weed whacker bike. It skips going up hill and can acutally choke down if you try to start it uphill and give it gas too late and drop the clutch. It is a finicky lil thang.

I also ordered a 31cc ryobi weed whacker engine on ebay. I might have wasted my money, but I'll see. The best I can tell, my bike with the 33cc chain saw will run like a scalded dog on the flat and I mean I haven't had a flat long enough to wind it out yet, Not sure I have enough courage to do that,

25cc just won't quite make it up a hill without a good head start from before I get there. the 31 might be perfect.

If you are using a 33cc or high for sure use a small drive wheel. The small wheel has better pickup and the big one better top speed. Well mine is slow to get there but i'm sure it will fly, doesn't seem to have much toque either on hills. Im going to try to rig up a smaller drive wheel.
 
I spent the morning doing some basic research that I should have done long ago. It isn't all about the engine it seems to be at least 50% about the amount of tension on the drive wheel.

On electric drive bikes I have always just put a good strong spring on it and it works fine. Gasoline is not at all the same as I am learning.

I had a feeling gasoline was different but never really tested the theory out well. So today I did it. I removed the slap dash tiedown rod and mounted a single rod from the axle hub to the very rear of the engine support. The tension was pretty strong so off I went. I got about half of the course done when the engine said no more. When I tried to pedal it was a nightmare. Way harder than it should have been with so small an engine.

I got back home and pulled the tie down bar. I turned the holes on each end into slots. I lengthened them to allow for less friction. It was better but still didn't do what I wanted. I slotted them more to loosen up the tension.

The ideal tension. I found. is a lot less than you think. In reality the engine's drive might not need more than to just rest on the tire. When I started. the drive wheel skipped when put under stress. The skip caused me to pedal of course but I realized after testing that it was no more than when there was more tension on the wheel. Skipping sounds like a bad thing but I'm not so sure that it is.

A tension that is too small makes it hard to start the engine because the drive does not turn fast enough, but too much and it bogs down on the hills worse. Somewhere there is optimum tension and I plan to keep looking for it.

The lesson learning is that the amount of tension may be just as critical as the size of the engine.

I bought a 31cc ryobi engine on ebay. I will have to see if I can get it started and if it makes a difference. The big 33cc chainsaw is on the back burner for now. It is the ultimate power which I have dealt with. I would like to see if the cheaper, easier to find, and work with 31cc will work well enough. The 25cc is very close to being enough.

To be honest I have ridden about eight miles with a lot of different tensions today and I'm pretty exhausted. I really need to wait till tomorrow and start fresh. I want to test the tension from my last adjustment before I call it a day. What I am learning I can carry on to the next build so it isn't a waste.
 
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Todays lesson class"

Never drag your 2stroke friction drive when it is out of gas.

I was out riding the weed whacker today and ran out of gas without knowing it. I have my drive set up to just stop when I stop the bike, then start when I start to pedal. I stopped it at a stop sign then pedaled it up. The bike started and ran a bit. I was pedal assisting it when it got harder to pedal. So I pedaled harder of course. Then it seized.

At first I thought i just overheated. I was cursing it's small size till I noticed the empty gas tank. I had run forced the engine to turn over with no lubricant. I have no idea if the engine is ruined or not, but I know it is pretty much locked up now. I'm going to let it cool down then see what kind of damage I have done.

new rule for me....ALWAYS FILL UP BEFORE EACH AND EVERY RIDE...
 
Well the engine isn't completely ruined.

I got it started and ran it a half mile but it was tough to start but seemed to finish strong. I'm going to let it rest a while as I do the same.
 
The bad news is the motor knocks... It runs almost as good as before but it sounds like it's going to fly apart. I'm going to swap it out for the 31cc I have coming if it will run.

So boys and girls we all know now not to turn the engine over without gasoline. At least not much.
 
I was asked for pictures of my engine mount so here it is.
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I made a couple of quick drawing to further illustrate the hardware to connect the engine to the bike frame.
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not long ago on this thread someone mentioned using a 2x4 for a platform to mount the engine. I have given it some thought and plan to use a 2x2 on my next build instead of the expensive angle brace. All that specialty hardware is expensive but none so much as the angle brace. I would like to put together the least expensive mounting technique for my how to instructions.

Anybody know of any reason right off hand that a 2x2 won't work.
 
Neat times... didnt you say you bought some goped spindles. If so what is the inside diameter of the opening. Thanks..
 
Deacon, try and keep the cooling shroud on the new one. I still like your ingenuity, if you were closer I would have you come over and pick through the stuff I have and get some of it out of here. I have saved every little engine and parts for the last 30 years. I have so much of it I have to hold a camera into the pile to see what is in there. Have fun, Dave

PS: To bad you had to learn about the oil on the parts the hard way. That engine has an Aluminum cylinder no chrome, but it is also a 1 bearing engine and you are putting a lot of pressure on the crank with that roller. Good luck with the 31cc.
 
About the gasoline running out, I know it should have been intuitive but I really had no idea. Been hanging out with too many four stroke engines.

I think the 31cc is going to prove the death of me. If it starts this morning I will know for sure that I have screwed up. I had planned to drag start it but I have never had one do that successfully. I think it is a matter of how fast the thing has to turn to start. The same is true with the chainsaw.
 
Friction drive seems to be the most simple way to get power to the ground. A 25cc engine seems pretty small.

Scott :ride2:
 
Deacon I Just Read Your Question About Friction Drive Roller Inside Dia. It Is 1/2 ". It Has The One Way Brg Inside. 1 1/4 " Od. With A 31cc Engine I Think Your Drive Roller Should Be No Larger Than 3/4" Od. Thanks For Answering My Question About The Clutch Housing Bolt Pattern. I Better Also Say ; With The One Way Bearing You Ca Not Start You Engine By Peddeling The Bicycle, It Will Just Free Wheel. ^5 RON
 
I couldn't use it anyway. I have to have enough room to maneuver a socket wrench inside. The threads on the new 31cc I have is 5/16 The nut is half inch od and the socket would be a little more.

The drive wheel I am using is 1 1/4 outside diameter and it is bogging down on the hill climb. I have to fine tune the thing tomorrow and probably the rest of the week. I broke down and bought a new weed whacker just for the engine. It sure is nice to have one that actually starts when you try to start it. It won't drag start either.. Too much compression I think. Unless it's running it skips over the tire too much.
 
The solution was too simple, too obvious. I would never have thought of that.

Many thanks,

Scott :ride2:
 
n7net said:
Friction drive seems to be the most simple way to get power to the ground. A 25cc engine seems pretty small.

Scott :ride2:
Click to expand...

with how I worked out my Carb and exhaust on my 21cc you can still get enough power with out putting money into it just lil tweaks.

I was doing about 18mph and over 100mpg before I wrecked yesterday. who knows having it at my cousins for a week i will get back over there and he will have a super charger on it. haha
 
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