Curiosity about centrifugal clutch

Khalil Brooks

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May 10, 2020
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I’ve learned how a centrifugal clutch works in comparison to the stock clutch on the kits. That being said what would be the pros and cons of switching? Are you able to manually engage and disengage the clutch without changing the throttle position? Would going downhill with such a clutch speed up the engine rpm and engage the drive train? I understand the the concept behind the centrifugal clutch but any additional info is appreciated.
 

Agreen

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Feb 10, 2013
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If you're referring to the one offered for the china 2 stroke kits, then yes. There is a one way bearing on it that allows for bump starting. You have to leave the original manual clutch installed if you want to pedal without the engine turning. When you come to a stop you don't have to pull the clutch lever, and you just twist and go.

I did a YouTube video on how to make a spacer for the centrifugal clutch kit. They really dropped the ball on manufacturing them and made the case too thin. If you use your old over and cut it up you can space it out far enough and it'll work. Others have had success with using a stack of clutch cover gaskets.
 

Khalil Brooks

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May 10, 2020
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More questions. The way home from work includes a steep acsent of maybe 500ft in a mile or less....not sure about the quantitative measure of the grade but the length and steepness of the hill is about at the limit of what my little 66cc can handle with a 195lb man on it at full throttle. That being said I essentially can’t stop on the hill bc I’ve removed the pedal chain (space reasons I haven’t yet sorted out). I was wondering if throttle/clutch control using the centrifugal clutch would be more fine tuned than manually releasing the clutch ever so slowly. My original intuition is that my hand might have better fine control over the clutch than the centrifugal clutch would allow, but I have no experience trying it out.

Anyone got ideas?
 

wheelbender6

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Sep 4, 2008
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I kept my hand clutch when I added the auto clutch so that I could still pedal start. It required some grinding, but it wasn't difficult. That approach may work for you.
 

Agreen

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Feb 10, 2013
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What you're referring to is called "feathering" the clutch. On a car this is done only momentarily to get it rolling, then the clutch is fully engaged. It's the only time the clutch wears, and is actually very bad for it, but it's necessary for initial takeoff.

On the bikes it's the same story. The centrifugal clutch should only slip during initial takeoff and then be fully engaged afterwards. Too much feathering and it will overheat. As the friction pads heat up, they'll start gassing off and it won't grab the friction surface any more. Continue to do that and the clutch will be completely smoked and you'll be changing it out soon.

If you need the assistance getting up a hill, try a shifter kit. They're not cheap, but it's what you need. You can then use your rear derailleur to shift gears and life will be much easier for you and your bike.
 
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forties

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Jun 2, 2017
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Would want a nice big easy to hit kill button on a centrifugal bike. Was just looking at an old morini ktm junior.. was thinking about what to do if it sticks wide open. You can't just grab the clutch lever like you could on a normal bike. Stick a newb kid on one of those you better explain well about that kill button, **** happens.

Wear is the other big downer I could see like green said. And the PITA of setting it up so it grabs correctly. I'd probably try to get it to grab quick at low rpm in order to reduce wear.
 

Guy Marquette

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Jul 30, 2020
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Hi everyone,
Hoping it's cool to piggyback on this thread.

I've bought and received the kit for my china 66cc engine. The best install vid I see is one by Fabian, which is good info and well appreciated.

1) the extension sleeve that's supposed to go over the crankshaft output (where the original small helical gear and woodruff key was)....Fabian's vid shows and discusses this part just fitting onto the shaft. Mine is very tight....which in some ways makes sense given there's no keyway or splines, so nothing but friction connecting the crank to the drivetrain. But I guess the question is other than smashing it on there with a hammer, what are you guys doing to install this thing on the crank?
Is there something I'm missing here?

thx in advance!
 

FOG

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Mar 3, 2019
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Assuming we're talking about a tapered shaft and sleeve a normal amount of torque will jam the tapers together. You'll probably need a puller to get them apart.
 

Guy Marquette

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Jul 30, 2020
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I suppose my concern is getting it on there straight...which seems unlikely with just pounding it. I guess I may have to figure out some kind of press.

the kit did come with a puller, the extension sleeve is threaded on the end. There is a part of me that doubts that a part that so tightly fit that it will friction-connect the engine with the drivetrain will pull out instead of stripping the threads. I dunno. I think normally I'd just go for it, these engines are el cheapo, but in this case I was hoping to install it on a nice, kinda spendy GT90 case reed setup, and I'm really trying not to F it up.

Maybe I'll install it on another engine and just see how it goes. The mental image of just whaling this thing on there bothers me, but maybe that's just how this goes.
 

FOG

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Mar 3, 2019
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The mental image of just whaling this thing on there bothers me, but maybe that's just how this goes.
I can understand that. It'd make me a bit nervous too. :)

FWIW, I've known people that have ditched the key on a flywheel to get optimum ignition timing. Taper's can definitely hold that. Not the same thing tho.
 

Agreen

Member
Feb 10, 2013
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The taper of the shaft is what holds the torque. The keyway is for alignment. This is true only on tapered shafts though. On a straight shaft it absolutely does hold the torque, and it's a far inferior design.