Moterized bike help?

[mattmanfirsttimer]

Hi guys, i"m building a moterized bike with a 1.2 HP weed whacker engine, i was looking at some sites wondering what size and type of centrifugal clutch to use and they said not to use big wheels, this is a problem because i wanted to use a centrifugal clutch because they are cheaper than a torque converter.So my qustion is, what can i use that's cheap and still works with bike wheels.

Also i still wanted to be able to pedal because i dont think 1.2 HP can pull me (180 pounds) and the bike which is at least 20, thanks!

P.S. this is my first time so i dont quite know the lingo

 

[landuse]

Welcome to the forum. The problem with a bike and a cent clutch is that the wheelsvare too big to get a decent low gear ratio to actually get the bike moving and not burn the clutch out. As one of the Karting gurus on this site said, you should generally get a axle sprocket 80% the size of your tyre. This could be ridiculously big, so a jackshaft will be needed to use smaller gears

 

[mattmanfirsttimer]

Thanks! only one problem.... i have no idea what a jack shaft is. Ill look it up and see what i come up with.

P.S my recorces are limited to basic tools some spare bike parts and about 30$, is their anything i can do that? or should i wait and save up for some better tools and parts?

 

[mckutzy]

A jack shaft is a shaft with sprockets to change the gearing, to change the drive side, to have a better alignment with a wide or narrow rear tire or the mounted motor with a larger length PTO shaft.

Id wait a bit, learn about the bikes and build up some cash. if your a fast talker you might be able to swing yourself some deals for parts, but ya money is going to be required.

 

[mattmanfirsttimer]

Ok, ill do that then.

but while im here i might as well ask if there is any way to make it so i can pedal and have the engine run at the same time, im still in planing but i found that if i just use the gears already on the bike i will have to pedal at the same speed as the engine OR gear the engine waaaaaaay down so is can push me with out me pedaling but then it will have no speed. also i am going to try to make it so that one have it up to speed it can push me so i don't have to pedal, do you think that would work or would it be just to weak. and lastly i understand the jackshaft but i still don't know if i want a centrifugal clutch because i read that they burn out easily, so if price was no object what might an alternative be?

 

[mckutzy]

Now that is, Im not saying go away till you can come up with the cash....
By all means stay a while, there isnt a whole lot of the motorbicycle guys here, so if you got something to share, were all more than interested in listening to what you have to show off.

 

[ballinchestr]

Look into a motorbike kit. I built one of those this spring and it was a pretty sweet project. I know it's kind of "cheating" to buy a kit, but you still need to do a lot of work, and you'll end up learning a lot, just like I did. Depending on your state/country, you could even register it for street use, as a moped. I built mine on a $160 budget, not counting the bike I already had.
It has a manual clutch, which you have to get used to, but it allows you to start the engine by pedaling, and you can also pedal while the engine is running. From what I learned, you can get 49cc or 66cc engines. If you plan on registering it for road use, check your state laws regarding engine displacement.

Good luck!

 

[mattmanfirsttimer]

i was thinking of maybe takeing off the pedals completely and just having the engine, if i play with the gear ratios could that work?

i can use the front set of gears like a jack shaft and keep the back intact. if i do this i would buy the smallest clutch sprocket i could and have a have a 48 tooth input and a 28 tooth output, in the very back i have a 15,17,20,24,and 28 tooth gears.
in case i got the jack shaft thing backwards in the front i have a 48,38,and 28 tooth gear. would any of those work? thx!

 

[OzFab]

Welcome to the forum.

Please try to keep all your question relating to one project in the same thread

 

[mattmanfirsttimer]

need gearing help

i am building a mini bike out of an old bike and a 1Hp engine, i was wondering if i could use the front set of gears like a jack shaft and the back set could be used like normal, in front i have 48,38,and 28 tooth gears,in the back i have 15,17,20,24,and 28 tooth gears.
if i had the engine hooked up to the 48 tooth and the 28 hooked up to the 15 tooth could it move 180 pounds? im still in planing and nothing is concrete. i have a budget of 40$ and the only problems i know about is how tittle hp there is and the fact that centrifugal clutches,while they are the cheapest don't do well with big wheels, would the jackshaft fix that or not?

I have limited tools and very limited skills.

 

[ballinchestr]

i was thinking of maybe takeing off the pedals completely and just having the engine, if i play with the gear ratios could that work?

i can use the front set of gears like a jack shaft and keep the back intact. if i do this i would buy the smallest clutch sprocket i could and have a have a 48 tooth input and a 28 tooth output, in the very back i have a 15,17,20,24,and 28 tooth gears.
in case i got the jack shaft thing backwards in the front i have a 48,38,and 28 tooth gear. would any of those work? thx!

They might work, but still, 1.5 HP is a lot less power than you might expect...
Keep the pedals or maybe look for a more powerful engine.
Don't go too high though. Bicycles aren't built to safely support a powerhouse.

 

[mattmanfirsttimer]

i know,but is there a way to up the power without buying a new moter?

 

[ballinchestr]

i know,but is there a way to up the power without buying a new moter?

You could squeeze little bits of power out by modding it, but I don't know how well it will take that, considering it's a weed whacker engine.

Changing the gear ratio could give you more torque. Yes, more torque will pull a greater load, but at a much slower speed. It's a tradeoff.

 

[mattmanfirsttimer]

the moter was free so ill give it a shot, what do ya mean by modding it? modding it by taking off the limiter or more drastic like boring out the cylinders?

 

[firemanjim]

Just make it a roller type drive. Engine is geared down for torque, and spins a roller that rubs against tire to push the bike forward. It's the easiest way to build one with what you have at your disposal. Cent clutch for that engine is about $20.... A sprocket to build roller assembly, about $10..... You're gonna need about another $30 and maybe I can put all the pieces together for ya in that budget, with links to get the stuff....
Then you just gotta build it..... You need to post a pic of your engine if you want my help though. I don't want to waste my time if your engine isn't even compatible with what you're trying to do.
On a side note, yet you only have 1.5hp, that's quite a bit, if geared properly to push you around at a decent speed with out pedaling. But you will have to shut it down or assist on hills, upward slopes, ect.....

 

[mattmanfirsttimer]

I want to try to use the chain and gears, I did consider doing that (I call it a friction drive) but this is going to be the precursor to a real true mini bike so I want to learn about the ratios and get it right this time so next time it's faster and easier. Also I think using chains and gears looks cleaner that a friction drive.

 

[mattmanfirsttimer]

So far I've been told it's enough power and that it's nowhere near enough, does anyone know for shure?

 

[mattmanfirsttimer]

Will a centrifugal clutch work with bike tires?

I've been reading about centrifugal clutches and all the sites say they arnt for big tires, will they work with 24in bike tires?
If not why?

 

[landuse]

I have merged your threads

 

[mckutzy]

Typically the basic mods with any clone type motor are, air cleaner/ carb rejet, and a new exhaust.

But that is a 4stroke, 2stroke are different have a tuned exhaust and I think the carb is generally different aswell.
Post a pic of the motor you have.