Belt drive 2 stroke budget build

Will'smotobikes19

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Apr 9, 2018
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1,658
I've just been going through ideas I had after looking at a few old weedeaters, of course these engines are very small I wouldn't go under 25cc and pedalling would be neccesary. If you could attach a pulley to the shaft while still keeping the pull start then you could build a mount for the engine to stay in place and have a heavy spring belt tensioner to act like a clutch that uses the same clutch lever for the 2 stroke kits. Or maybe do the same thing for the regular 2 stroke kit engines, release the clutch while pedaling. The only problem with these old engines is the carburetors they have diaphragms that go bad constantly. I have an old 25cc homelite trimmer that I know runs and an old ryobi 31cc trimmer that might need a new coil. You would have to put a sheave on the wheel for the belt. Maybe you could even make a 2wd with friction drive on the front and belt drive on the rear! ha the only thing is you'd have to use a more powerful engine on one of the wheels atleast I think that's what someone said. Or use an electric hub wheel on the front and have the small 2 stroke setup on the rear. They make a dual cable brake lever you could use to attach the 2 throttle cables together if it was 2 engines.
 


Frankenstein

In memory of Frankenstein 1991 - 2018
Joined
Jun 24, 2016
Messages
5,077
I've just been going through ideas I had after looking at a few old weedeaters, of course these engines are very small I wouldn't go under 25cc and pedalling would be neccesary. If you could attach a pulley to the shaft while still keeping the pull start then you could build a mount for the engine to stay in place and have a heavy spring belt tensioner to act like a clutch that uses the same clutch lever for the 2 stroke kits. Or maybe do the same thing for the regular 2 stroke kit engines, release the clutch while pedaling. The only problem with these old engines is the carburetors they have diaphragms that go bad constantly. I have an old 25cc homelite trimmer that I know runs and an old ryobi 31cc trimmer that might need a new coil. You would have to put a sheave on the wheel for the belt. Maybe you could even make a 2wd with friction drive on the front and belt drive on the rear! ha the only thing is you'd have to use a more powerful engine on one of the wheels atleast I think that's what someone said. Or use an electric hub wheel on the front and have the small 2 stroke setup on the rear. They make a dual cable brake lever you could use to attach the 2 throttle cables together if it was 2 engines.
A slightly slicker method would be a double pull cable that would operate 2 cables from a single line, you can retain a normal throttle that way. If they aren't of equal power then maybe one should be given a thumb lever instead.
dual_brake_cable.jpg


If something kooky like 2 gas engines is going on and you have a difference in cable travel between the 2 different carbs from closed to wot then you can make something similar to the travel agent made by park tool to convert short pulls into long ones for brakes (or vice versa.) The difference in size between the 2 rollers is just simple math once you have the nominal wot pull length of each carb.
ta-in-line-pulling.jpg


A small lever would also work, a pivot at one end with a cable pulling on it, 2 cables at different spots down the length of the lever would give different lengths, though the roller adaption is far more robust and acts as a natural cable guide, making it easier to make simple since it really eliminates pinch and bending points that wear and break cables.
 
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HeadSmess

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May 17, 2010
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3,049
i have never, ever had a diaphgram go bad yet. clogged bits, blocked bits, water, dirt, you name it...but still no diaphgrams have ever required replacing...in my experience.

maybe its the brand engine you use? ryobi? homelite? chuck them in the BIN, and get a decent commercial engine...shindawai...kawasaki...stihl...robin... the ones that actually get used all day long for years without any issues. when your shaft wears out before the engine needs anything more than the airfilter cleaned...its a decent unit.

ryobi and homelites are just jokes. cheap and nasty pieces of junk. and they dont lend themselves to being modified too easily, either.

a little stihl ms180 chainsaw engine would be the ideal choice... nice big fat mounting lugs and very little attached to the engine itself...small and compact.

anyways.

belt drive...

the only real issue with belt drive is the pulley radius and speeds...

you need a small drive pulley to get sufficient reduction.

the engine speed is so high you need a very small pulley to keep the belt attached to the pulley. remember, modern engines are idling at the same sort of RPM as what early engines where doing at full throttle... back when harleys used flat belts drives... (and they havent progressed much since then either!)

v-belts dont like running at high speeds over small pulleys. and they are very inefficient when run as such.

chains are just damn SCARY! and you need a clutch...

the best bet is a flat belt drive, then you can get away with a drive pulley of even 1/2 an inch in diameter...

the problem is getting hold of decent flat belts... noone makes them or uses them much anymore. you ideally need leather, preferably chrome tanned. not that hard to join. cheap. keep it well lubricated (lanolin, tallow, lard or glycerin) and it will give a long lifetime. dont use resins or other "anti-slip" compounds, they end up causing more slip, ironically.

the slip belt clutch works fine, makes the belt easy to replace, and you can engage it gradually . it also makes the engine much narrower than if you use the existing clutch bell...that requires a housing as well due to where its bearings are located.

and with a slip belt clutch...you can simply rip the starter assembly off anyway...making the engine even narrower!
 
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Will'smotobikes19

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Apr 9, 2018
Messages
1,658
Yeah they are kind of crappy engines but I got them for free, and they run it may be my fault because I think I left gas in them for months. I also have a 33cc chainsaw engine that runs its also a homelite it had problems running though I think it needs a clutch. Oliver motorized on youtube made a 2 speed belt driven 79cc bike with foot pedal clutches. Maybe a Honda gx25 or gx35 would be better for the belt drive idea but I thought why not use these few engines I got for free.
 
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