centrifugal clutch mods

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hick185

New Member
Oct 12, 2008
9
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Tell City, Indiana
hey guys i've built a motorized bike using a 27cc weedeater engine. i mounted the engine in the frame and used the pedal crank as a jackshaft. the bike is a 26'' mt bike. i used a custom made ten tooth sprocket on the output of the engine which runs a chain down to a 48tooth sprocket on the left side of the jackshaft. On the right side of the jackshaft i have another 10tooth sprocket going to a 48tooth sprocket welded to the rear cassette. I have a 23 to 1 gear ratio and the bike does take off on its own power, but a lil slow. It tops out about 25mph(guesstimate no speedo). the bike rides great but i wish i had more take off with out sacrificing top speed. I noticed that the clutch starts engaging at a pretty low rpm. My thinking is that if i could keep the clutch from engaging util the engine is at a lil higher rpm it will take off easier.. But that is what i'm thinking i haven't had much experience with centrifugal clutches so i might be wrong. Is there any way that i can keep the clutch from engaging until a higher rpm?? I think lightening the weights in the clutch would work but i'm not for sure..

So if anyone knows how to make the clutch engage at a higher rpm please let me know how..
 
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hick185

New Member
Oct 12, 2008
9
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Tell City, Indiana
i forgot to say that the reason i think that having the clutch wait to engage util a higher rpm is so the engine is higher in its power band. therefor having more power when taking off. sorry if my post is a lil hard to read or understand i am extremely tired. anyway thanks for reading.
 
diceman2004

diceman2004

New Member
Aug 26, 2009
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Kitchener , Ontario
i cant see any real advantage to your clutch engaging at a higher rpm .
personally i think , the combinatin of the size of the motor and the gearing sets the limit of what you can do , without having gears you can change .
i think the only thing you are going to do by changing the clutch rpms is cause your clutch to heat up faster , since your gearing hasn,t changed , your motor will still have to move the same amount of mass with the same amount of power from a standing start . everything beyond that is just clutch slippage and heat generation .


anyways , thats how i see it . its a trade-off , low end power for top end speed

and don,t forget , you will also be increasing the slowest speed at which you can ride under power . eg: if now your bike will drive say 10 mph slowest speed , after you change the clutch you might be at 15 mph slowest speed .

that means now you have to pedal under everything less than 15 mph instead of 10 mph .

i think a clutch should engage at the lowest rpm possible without stalling out the motor
 
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hick185

New Member
Oct 12, 2008
9
0
0
Tell City, Indiana
the way i have my bike set up i don't have pedal on it. so its all engine power. The way i was thinking is like a higher stall converter put in an auto transmission. Or on a manual holding the rpms higher then slipping out the clutch. I think that the engine would still have the same speed down low and up high. The engine would just have to be at a higher rpm to take off.. I don't plan on messing with the clutch this was more a "hypothetical mod" then a real on. If anyone has anything to add go for it. I'd like to hear more.
 
professor

professor

New Member
Oct 14, 2009
500
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Buffalo ny area
A high stahl converter makes a lot more heat because of the slippege. In your case, you will melt the clutch. Just like in a manual trans car that the driver revs high and lets the clutch out slowly.
Looks like you are kind of stuck on gearing any lower, which is what you need. Can you switch to a 24 inch back rim? Would help a little. A 20" would help a lot!
 
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hick185

New Member
Oct 12, 2008
9
0
0
Tell City, Indiana
yeah i've thought of heat but when i pulled the clutch apart to look at it everything is made of steel. There is no organic friction material in the clutch to burn up like on cars clutch. There is not any bearings either. Just a solid metal bushing. Like i've said before i'm not looking to actually do anything to the clutch I was just wondering if there is anything that COULD be done.
 
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jcchappy

New Member
Aug 18, 2009
144
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antlers, ok.
talk to pocket bike racers there is definately an advantage to getting the stall way up there. our bikes produces somewhere around 5hp from a true 50cc big bored 39 cc cagulari pocket bike these werent stock by no means but they had 3 shoe clutches. we changed the to 2 big shoes. we also would always but heavy duty springsm in the that would make the engine rev way higher before take of. it was like take you 5 speed car pressing the gas to the floo then dumping the clutch while you had it in first. heavy duty spring or lighter weights do the trick far as stall is concerned. research scooters pocketbike and moped clutch far as hop up mods to the clutch you will find what i'm talking about.
 
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