Have few questions for a friction drive build

[Chuddybuckrivet]

Hey folks. New guy here. Great forum yall have here. I've learned quite a bit already. Ever since I was a kid I've wanted to build a motorized bike. So almost 40 years later I'm going to do it!

The thought came to mind when I recently dug an old Echo hedgetrimmer (not a weedwacker) out of my shed that someone gave me a long time ago. Well, I don't have any hedges, hence it sitting in my shed for the past 10 years. It's got a 21cc engine.

So my questions are, first off, is this little engine even worth using? Seems to have a ton of compression when I pull the pull cord. Almost feels like pulling a chainsaw cord. At least compared to my weedwacker and leaf blower. So I'm assuming it should have some torque? I'll only be using it use it to putt around my neighborhood maybe down some gravel roads thru the woods around here. If it will do 15-20mph I'd be plenty happy. It wont be a daily commuter or anything.

So assuming it's worth using, which side of the engine do I want to put my drive spindle on (I think I'm going to use a modified bmx peg or a deep well socket to start with?) I've seen various projects online where the drive spindle is mounted on the flywheel side and in other cases it's on the other side of the engine. What's the difference? I wont be doing much stopping and going, so if it doesnt have a clutch, I'm fine with that. Same goes for the pull cord, don't really need it, pedal start is fine with me. Not sure how I would even mount a shaft to the clutch anyway (I think that's a clutch in the below pic?)

I'm sure I'll have more questions along this build, but this is the first thing I need to determine so I can build the engine bracket to attach it to the bike. I'm a hobbyist welder/fabricator so I shouldn't have much trouble there.

Thanks for any insight you can offer. If I've posted this in the wrong place, I apologize and the mods can move it where it belongs.

 

[5-7HEAVEN]

Hey folks. New guy here. Great forum yall have here. I've learned quite a bit already. Ever since I was a kid I've wanted to build a motorized bike. So almost 40 years later I'm going to do it!

The thought came to mind when I recently dug an old Echo hedgetrimmer (not a weedwacker) out of my shed that someone gave me a long time ago. Well, I don't have any hedges, hence it sitting in my shed for the past 10 years. It's got a 21cc engine.

So my questions are, first off, is this little engine even worth using? Seems to have a ton of compression when I pull the pull cord. Almost feels like pulling a chainsaw cord. At least compared to my weedwacker and leaf blower. So I'm assuming it should have some torque? I'll only be using it use it to putt around my neighborhood maybe down some gravel roads thru the woods around here. If it will do 15-20mph I'd be plenty happy. It wont be a daily commuter or anything.

So assuming it's worth using, which side of the engine do I want to put my drive spindle on (I think I'm going to use a modified bmx peg or a deep well socket to start with?) I've seen various projects online where the drive spindle is mounted on the flywheel side and in other cases it's on the other side of the engine. What's the difference? I wont be doing much stopping and going, so if it doesnt have a clutch, I'm fine with that. Same goes for the pull cord, don't really need it, pedal start is fine with me. Not sure how I would even mount a shaft to the clutch anyway (I think that's a clutch in the below pic?)

I'm sure I'll have more questions along this build, but this is the first thing I need to determine so I can build the engine bracket to attach it to the bike. I'm a hobbyist welder/fabricator so I shouldn't have much trouble there.

Thanks for any insight you can offer. If I've posted this in the wrong place, I apologize and the mods can move it where it belongs.

 

[5-7HEAVEN]

It seems like the easy way to do a friction drive is to bolt a 3/4" deep socket onto the flywheel. That's the business end that'll press against the tire tread.

You'll get more throttle response using the smaller-diameter socket than from the large-diameter BMX peg.

If the flywheel spins clockwise, mount the engine on the right side of the bike.

The other side of the engine seems to have a clutch. You could mount it on the clutch side, but you'd have to find the bellhousing, which mounts onto the engine with the 4 holes in a square pattern. If the clutch spins counterclockwise, mount the engine on the bike's left side.
If you don't mind the engine dying at a stop, mount it firmly on the bike.

If you want the luxury of being stopped or slowing down without the engine dying, then mount the engine on a hinge. Make a lever you can reach to lift the engine off the tire when slowing down to a stop.

This option will also allow you to pedal the bike easily if the engine doesn't run, or you just want to pedal the bike around quietly.

It's an easy DIY. LOL, it takes a bit trying to explain it.

Make sure the brakes work well, and have fun!

 

[Chuddybuckrivet]

Thanks 5-7. I have far more options if I mount it on the flywheel side so I'll go that route. And yes the flywheel spins CW. I plan on fabricating a hinge type system either way but I'll start with just a turnbuckle for tension till I see what this engine will do, before I get too elaborate and make a lever operated engage/disengage system. Think this little engine has enough balls to push me 15-20ish mph? It's going on a beach cruiser style bike and I weigh about 150lbs. Thanks again.

 

[5-7HEAVEN]

Thanks 5-7. I have far more options if I mount it on the flywheel side so I'll go that route. And yes the flywheel spins CW. I plan on fabricating a hinge type system either way but I'll start with just a turnbuckle for tension till I see what this engine will do, before I get too elaborate and make a lever operated engage/disengage system. Think this little engine has enough balls to push me 15-20ish mph? It's going on a beach cruiser style bike and I weigh about 150lbs. Thanks again.

Have fun installing the engine.
This engine should easily get you to 15-20mph on flat ground.
My first friction drive had a 35cc 1.5hp engine on a 20-inch folding bike. It ran 27mph tops.
My cruiser bike ran 30-something mph with a single 2.2hp Mitsubishi 43cc engine.
Then I installed a second Mits engine on the front tire. Bike ran 40mph, cruised at 35mph.
Then I installed a 4.5hp CY460 on the rear of two different mountain bikes. Bikes ran 45mph tops.
I weighed 185lbs. back then.
All bikes were friction drive, which I don't do anymore.
I must've used up over 20 tires.
Now I use chain drive on my motorized bikes. My tires last for years.
My top speed now is 43mph.
I weigh 210lbs now.

 

[5-7HEAVEN]

If you fabricate a support for the outer side of your roller, you'll have less chance of damaging the flywheel and crankshaft.

 

[Chuddybuckrivet]

Would it be ok to use my welder to put a bunch of "knobbies" all over the drive roller? I'm using a 3/4" socket and it's obviously very smooth. Or would I better off doing the epoxy and sand coating?

 

[5-7HEAVEN]

I'd definitely go with the knobbies.