New Engine!!! Need help about chain drive

brendonv

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Well today i went to the tip looking to see what sort of engines they have and the prices so i no for a project later on. My dad is good friends with the lady who owns it, he brings scrap metal there all the time, anyway i was looking around and came across a Ryobi Weed Wasp, its basically what i have already but a centrifugal clutch as well XD Im thinking i need a clutch because its a bugger when u stop then u gotta crank it over again to start it so i cant really stop at intersections. Well i was looking at it and it looked almost new, just cracked fuel lines and a primer bulb exactly what i had on my other one, so my dads like u want it? I was like ohh ill see what she wants for it ( im thinking 40-50 as there 140 new ) she goes 10 bucks love. Im like think wtf are u serious so i quickly give it to her and run lol. Well if it doesnt work its only 10 bucks and i can salvage it for parts. If it does i have two options, fix it then sell it then buy myself a better engine or use it.

Im thinking chain drive since it has a clutch, my dad reckons i need to keep the pull start on or i cant start it, if i make it friction can i still start it with that or does it need the pull start? What sort of gear reduction do i need for this if i do make it chain? Also where do i measure the RPM from? The engine from idle or at full?

Thanks guys. I really want to make it chain as i hate it that i cant ride in sand, wet or on grass well.

From Brendon.v
 
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Well today i went to the tip looking to see what sort of engines they have and the prices so i no for a project later on. My dad is good friends with the lady who owns it, he brings scrap metal there all the time, anyway i was looking around and came across a Ryobi Weed Wasp, its basically what i have already but a centrifugal clutch as well XD Im thinking i need a clutch because its a bugger when u stop then u gotta crank it over again to start it so i cant really stop at intersections. Well i was looking at it and it looked almost new, just cracked fuel lines and a primer bulb exactly what i had on my other one, so my dads like u want it? I was like ohh ill see what she wants for it ( im thinking 40-50 as there 140 new ) she goes 10 bucks love. Im like think wtf are u serious so i quickly give it to her and run lol. Well if it doesnt work its only 10 bucks and i can salvage it for parts. If it does i have two options, fix it then sell it then buy myself a better engine or use it.

Im thinking chain drive since it has a clutch, my dad reckons i need to keep the pull start on or i cant start it, if i make it friction can i still start it with that or does it need the pull start? What sort of gear reduction do i need for this if i do make it chain? Also where do i measure the RPM from? The engine from idle or at full?

Thanks guys. I really want to make it chain as i hate it that i cant ride in sand, wet or on grass well.

From Brendon.v

Yep, with a centrifugal clutch you would have to keep the pull start as you cant bump start a centrifugal clutch because it is only engaged once the engine is on. Should be a cool new project!

Fastboy
 
**** yeh, i hope i have some fuel line somewhere as its sunday 2morrow and the lawnmower shop will be closer :( Can wait till i get it all cranked up, a clutch will be cool, i can tell it has a clutch wen i pulled the pull start the end snipper part didnt turn. XD gtg to bed now lol if i can sleep, its going to be fun 2morrow. Can never have to many engines.
 
For a chain drive you'll need about 19 or 20/1. An HT wheel sprocket and a jack shaft should get you there.
 
What is the displcement of this Ryobi.To get the reduction,divide the displacement into 1000, the result is a ballpark fgure for the reduction (26" wheel),let's say you have 40 cc ,1000/40=25.If you have significant hills, go higher.
 
With a 26" wheel & 25/1 at 7k you get 22 mph @ 6k you get 18.8 mph. Better than pedaling but not by much.
 
These are rough ballpark figures,including hills,based on the fact that engine torque is proportional to displacement,in the flats you could use 800 instead of 1000.Helping out if you run out of torque going up hill is exhausting,the luxury of high speed is nice if you can get away with it.
 
this ones a 25cc so 1000/25= 40, so does this mean the motor would rotate 40 times for one revolution of the 26" wheel?

I was thinking of gear reductions and a frame mount having the shaft of the motor on the right side then have a chain from a little sprocket on the engine to one of the sprockets on my gears on my bike then somehow put another sprocket on the other side of the pedals and run a chain from that down to the back wheel where there will be a HT sprocket. I think if seen this mount before, it would be safer having a rack mount but if i have a frame mount its less noticeable which is what i want. Would a 2 stage gear reduction be enough? What Tooth sprockets do i need for this job? Thanks, pics of others gear reductions would be nice if anyone could get em.

Cheers,

From Brendon.v
 
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sounds fun

Well to figure out the reduction, you can get a ratio calculator, just search for it on this website. On my bike i have an echo weedeater engine rack mounted. it has a 6 tooth sprocket on the engine going to a 43 tooth, then attached to the 43 tooth is a 14 tooth freewheel going to another 43 tooth sprocket on the back wheel. its not real fast but i had to gear it low because it is only a 22.8cc my top speed is about 25. sorry i cant get any pictures because if have dialup and im getting ready to go to bed(i have to get up at 4:30) but anyways, i wish you luck. Keep us updated. have fun.
 
Torque is also determined by compression ratio, port timing and a host of other issues. My R460 is just getting into it's torque curve when my wifes TLE43 tops out. A benefit of more power is the ability to cruise at good speed with little stress on the engine. At a 25 mph cruise, I'm lugging a little, at 30 it's starting to breath right.
 
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