Centrifugal Clutch One-Way Bearing Won't Engage

Discussion in 'General Questions' started by Louie, Aug 22, 2016.

  1. Louie

    Louie New Member

    Just installed a centrifugal clutch on my 66cc engine (which has been running fine with a friction clutch for 200 miles). Can't pedal it at the moment because the cranks don't clear the case. To try and start it, I just coast down my driveway and then pop the friction clutch. I'm getting nothing but the clutch bell spinning. When i slowly walk the bike, I can get the one way bearing to engage but nothing beyond that and certainly not long enough or securely enough to get the engine to start.

    What am I doing wrong? Does the bolt that holds the whole assembly together need to be even tighter?

  2. Chopper bicycles

    Chopper bicycles New Member

    Check key on clutch my shaterd once on the fricton drive
  3. Louie

    Louie New Member

    That's not the problem, the friction clutch is still transferring motion to the bell of the cent clutch. Somehow the one way bearing only engages when I mess with it.
  4. KCvale

    KCvale Motorized Bicycle Vendor

    You need the other half of the kit bud, another way to start the engine.

    The only way to start a CF clutch engine is with a pull start or electric start on the engine.
    The Zelda (or whatever it was called) engine kit has a CF clutch but both a pull start and an electric start ability and an internal power source to keep the battery charged.

    Your drive is connected to the bell, and it don't matter how fast you spin the bell, it's not going to magically squeeze in and grab the clutch pads, a running engine spreads them out to make contact.

    I have no clue what you are talking about with a one-way bearing in there with a CF clutch means either, or why one would be needed anywhere other than if you were jackshafting to use your bike gears to allow your pedals to not spin when under engine power.

    Done right there is no clutch lever, you just need a different way to start the engine.
    Last edited: Aug 23, 2016
  5. Louie

    Louie New Member

    No, with these clutches they have a one way bearing that still allows you to pedal start. I have been able to get it to engage but not enough to start the engine.
  6. KCvale

    KCvale Motorized Bicycle Vendor

    By all means please tell us about this magical CF clutch that apparently don't work!
  7. Steve Best

    Steve Best Well-Known Member

    Whoa KC, this is possible.
    Power from engine to wheel over runs the one-way clutch, has to go through friction pads.
    Power from wheel to engine engages the one-way clutch, will allow bump starting.
    I've never seen it, but I can see the theory on a CF friction clutch, not a CV belt type.

    One way clutches are either positive action ratchet types or sprag action friction types.
    If it clicks freewheeling it is a ratchet, if it is silent it is a sprag.
    We use one-way clutches (often called one-way bearings) in industry a lot and often in a similar application.

    If it slips it is usually a sprag clutch and it is usually a wear or lubrication issue.
    Basic mineral oil like Automatic Transmission Fluid (ATF) is the best lube for them.
    They will slip if motor oil, grease, moly, STP, graphite, teflon, synthetic oil, soap or wax get on them.

    Clean it out behind the seals with spray brake cleaner and relube with ATF.

  8. KCvale

    KCvale Motorized Bicycle Vendor

    Steve, I have no desire to quarrel in forums with you.
    I asked for a link or something to explain how there is some magical way to make a typical CF clutch fixed bell somehow engage typical clutch pads on and engine that it is off.


    When the running engine spins fast enough the pads held in by springs spread out to make contact with the bell and engage the drive.

    What the heck kind of SF clutch you have never seen that will work the other way are you talking about?
    Or should I go look it up in Harry Potter books, because you can pedal spin that bell as fast as you want but it won' engage the engine pads.

    Steve, all I am asking for is into on this system you bought that obviously hasn't worked for you, and why you somehow thougt it would is all.
  9. Nanonevol

    Nanonevol Member

  10. KCvale

    KCvale Motorized Bicycle Vendor

    Ya, it's hard to dispute actual pictures of how the thing works using actual MB parts.
    Don't get me wrong here... I love innovation!
    This just wasn't one that can ever work without another way to start the engine is all.
  11. Dustmonkey

    Dustmonkey New Member

    Like KCvale, it has been my understanding that a pull start or powered start is required when using a centrifugal clutch.

    Those centrifugal clutches need a bunch of RPM (like a couple thousand) to engage, and it is doubtful that you could pedal the bike fast enough to get the clutch to engage and cycle that force back to the engine to get it to fire.
  12. Steve Best

    Steve Best Well-Known Member

    You can't ever pedal a centrifugal clutch fast enough to start. The weighted clutches are on the motor side and unstarted, it does not move.

    If however, you had a one way bearing between the motor and the drivetrain it would turn the motor whenever the drive goes faster than the motor, like when bump starting. You would still need the manual clutch lever for pedaling with the motor off but with motor running, it would coast to a stop with no need of the manual clutch. I've never seen it built on a motorized bicycle but we use similar systems in industry to move conveyors from different drive sources or directions. Automatic transmissions use a similar system to get 2 forward and one reverse speed from a single planetary gearset.
    Dustmonkey likes this.
  13. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor


    Whizzer automatic clutches use a one-way bearing to allow pedal starting the motor, however not aware of any other drives that use them. We use the same clutch parts in our 4 stroke drive system as we do in the clutch systems we make for Whizzers, the major difference being the one-way bearing.
    Have fun,
    Dustmonkey likes this.
  14. KTOKTO

    KTOKTO Active Member

    A pedal start with a centrifgual should be possible with a sprag type of clutch with the manual clutch engaged right? Or am I missing something here? Searching this site for some of the key words pull up conflicting info but there seem to be quite a few people out there who have a one way clutch bearing and are pedal starting their centrifugal clutch bikes.

    I've been looking around for vendors of these types of clutches but everything I am finding is either sold out or a vague description in ebay listings.
  15. KTOKTO

    KTOKTO Active Member

    Is this what you are looking for? Start watching at 18:45 and you will see the sprag catch.

    Last edited: Sep 19, 2016
  16. Frankenstein

    Frankenstein Well-Known Member

    Ei yie yie people. On the centrifugal clutch kits for these 2 strokes is rather simple, I think it was Fred who made the video for installation, he even specifically mentioned a one way bearing.

    Basically, an extention is placed on the output shaft of the motor, on that shaft, in order from the inside of the motor out, is a clutch bell with a bevel gear on it, inside the gear is a one way bearing, this is an important part to keep lubed, after that is a clutch boot which is directly attached via taper or key to the extention. When the motor turns it will engage the boots with the bell which then turns the bevel gear.

    If you pedal the bike to start, then once you let the normal clutch go, and the large clutch gear engages the bell's gear the one way bearing starts turning the motor over because the motor is obviously moving slower than the bell's gear on the outside of the shaft. I drew a picture now stop thinking too much and get all picture book with it. Note091916_1_1.jpg
  17. KTOKTO

    KTOKTO Active Member

    Thanks for the drawing, I get it now. Harry Potter was right!

    Last edited: Sep 20, 2016
  18. Frankenstein

    Frankenstein Well-Known Member

    Magic's the best thing to happen to motors since science failed us. :p
  19. KCvale

    KCvale Motorized Bicycle Vendor

    I use two freewheel (one-way) bearings in my 4-stroke shifters.
    One on the output shaft so you don't drag the belt when pedaling with the engine off, the other is for the pedals so they don't move when the engine is on.

    Unfortunately I have not seen the magic ones yet ;-}
  20. I had the same problem thanks for the info