New Engine!!! Need help about chain drive

Discussion in 'General Questions' started by brendonv, Jul 12, 2008.

  1. brendonv

    brendonv Member

    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
     
    Last edited: Jul 12, 2008

  2. fastboy9

    fastboy9 Member

    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
     
  3. brendonv

    brendonv Member

    **** 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.
     
  4. kerf

    kerf Guest

    For a chain drive you'll need about 19 or 20/1. An HT wheel sprocket and a jack shaft should get you there.
     
  5. duivendyk

    duivendyk Guest

    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.
     
  6. kerf

    kerf Guest

    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.
     
  7. duivendyk

    duivendyk Guest

    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.
     
  8. brendonv

    brendonv Member

    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
     
    Last edited: Jul 12, 2008
  9. levsmith

    levsmith Member

    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.
     
  10. kerf

    kerf Guest

    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.
     
  11. duivendyk

    duivendyk Guest

    this 1000 figure is conservative,if hills are not a problem you could go to 750 and a 30:1 reduction.20mph corresponds to 270 rpm at the wheel (26").So at that speed your engine speed would be around 8k rpm,You could try 25 at 20mph you would have 6750 rpm.Take you pick.
     
  12. brendonv

    brendonv Member

    Well i just found out my engine is 31cc not 25cc lol, i got a manual of the internet and it has everything in it, how to clean it and other info like.
    Stroke: 31.75mm ( 1.25 in. )
    Displacement: 31cc ( 1.9 cu. in. )
    Idle speed RPM: 2800-3600rpm
    Operating RPM: 7000-8200rpm

    It tells me how to tune the carby and clean everything, its really good.

    Hope this info works.
     
  13. brendonv

    brendonv Member

    Can i do just a straight chain drive say, a 10T on the motor to a 55T on the wheel? According to the gear ratio calculator i would go pretty fast. Why do i have to do a 2 way reduction, atm im thinking ill just do friction drive again.
     
  14. duivendyk

    duivendyk Guest

    Yes you would go pretty fast,in theory at least,but you would never get there you would run out of torque (driving force) at some low speed.The engine torque at the wheel is multiplied by the reduction ratio,so in your case would be increased just 5,5 times and the the engine rpm would go up to that speed when this equalled the rolling resistance,at IDLE speed you would be doing over 50 km/hr.You need a 15-20 overall reduction.That's about what the friction drive would do for you.
     
  15. brendonv

    brendonv Member

    so your saying if i go from a 10T on the motor to a 20T then on to a 10T to a 40T on the wheel that should work well?
     
    Last edited: Jul 14, 2008
  16. duivendyk

    duivendyk Guest

    No, that works out to 20/10 * 40/10=8 ,you need 2-3 times as much, like 10 to 40 followed by another 10 to 40, giving a 16 overall reduction.If you live in the flats you could get away with that.Still pretty tall gearing in my estimation,around 4000 rpm at 30 km/hr (26" wheel)
     
  17. duivendyk

    duivendyk Guest

    For your further enlightenment I'll give you a handy formula(don't get all scared it's not all that bad).Here goes:
    S= 0.12 * rpm/ R , S, road speed (km/hr), rpm (rev/min),
    R is overall reduction.Lets try 4000 rpm, 16 reduction, we get: S= 0.12*4000/16 = 30 km/hr,take 5000 and 20 ,you get
    S= 30.You see it's easy
     
  18. brendonv

    brendonv Member

    So if i have a little hills what reduction should i do? 10 to 40 to 10 to 60?
     
  19. duivendyk

    duivendyk Guest

    Probably something like that (if you can find it),depending on what you call "little" ,less than 5%?.( for every 10 m you go up 0.5 m),or a just a short hill, just what do you mean.Be more specific.
     
  20. brendonv

    brendonv Member

    i have say a 20 degree incline for about 300m.
     
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