Centrifugal clutch ?

Discussion in 'Frame Mounted Engines' started by TWalker, May 10, 2008.

  1. TWalker

    TWalker Guest

    I think I know in general how a centrifugal clutch works: it engages itself as it starts spinning faster, negating the need for a clutch lever to engagage disengage.

    I'm not sure about one thing though> at low RPM is it completely disengaged? I'm considering using a pocket bike motor for a project and I want to know will it roll freely if the engine is off or idling?

    Any experience on durability of 2 stroke pocket bike motors compared to happy times?

    Thanks ahead of time for your help

  2. You would think if the engine was off it would never engage. That's because the clutch pads would not be spinning. Clutch pads not spinning means the spring would never let the clutch pads expand. It would stay disengaged and your drive wheel will roll freely even if you're going down a hill at 100 miles an hour.
    Now depending on how stiff your clutch springs are will dictate at what idle speed is safe for your drive wheel to roll freely. Now the stiffer the spring of course,the higher RPM you can have your engine before engaging.
  3. Simon_A

    Simon_A Member

    Yup, they are completely disengaged at low RPM. The shoe's are held to the hub with springs, different strength springs are fitted to the shoe arms dependant on what RPM you want them to lockup. Most air cooled stock clutches only contact around 2000+ rpm. Allows the motor to get some speed up and approaching the powerband so it doesnt bog down before takeoff.

    Depending on the powerband of the motor (primarily dictated my the expansion chamber of the exhaust) depends on when the clutch should engage. My race clutch only provides total lockup at 8000rpm just at the start of the powerband.
  4. TWalker

    TWalker Guest

    Ok great thats what I wanted to hear :)
  5. justin

    justin New Member

    Any idea if you could put one on an HT engine? I would love to play around with that. Any links would be good too. Tried the search, but maybe I'm doing it wrong. Didn't come up with anything good.
  6. Simon_A

    Simon_A Member

    I dont know if one would fit a HT engine, as mine is in the mail system as I type this.

    What sort of links etc.? are you looking for? Do you want photo's of a centrifical clutch? I dont know what you are asking for.
  7. adamtheha

    adamtheha Member

    I just found a centrifugal clutch for a HT engine on Ebay, here's the link


    You'll need a pull start for it as well, boygofast sells them also on Ebay. Altogether, this cost me about $140 over and above everything else I've spent on this build!
    Altogether I've spent
    $200 - Bike
    $165 - Engine
    $15 - Paint
    $120 - Lights
    $40 - Accessories
    $140 - Clutch parts
    =$680 Total
    Hopefully I could sell it for over $1000.
  8. I would be curious how good this works when you get it. It sure looks rough in the pictures.
  9. adamtheha

    adamtheha Member

    Yeah, it looks as though it was welded together after market, but hopefully they've mastered the technique and tested them before selling!
  10. fatboy67

    fatboy67 Member

    You can buy a 70cc HT motor that is already a pull start with a centrifugal clutch. For the same price as a normal clutch set up. the only thing is you would have to buy the cranks that are wide enough, so you can peddle.
    On ebay. They come up from time to time, but I don't think they sell as well because of the fact that you have to buy wider cranks.
  11. adamtheha

    adamtheha Member

    Sigh...I should have gone with a ready made one for $200. I've already spent more than that and I still haven't put the clutch on, because the guy didn't send me the gear puller! I'm not looking forward to pulling that little cog out...
  12. Most engine kits come with the gear puller. Alot of people just dont recognized it or know what it does. I believe they call it a sprocket puller. If you need a pic Im sure I can find one...
  13. adamtheha

    adamtheha Member

    I've seen the pullers, and none of the kits I sell come with them.
  14. ZnsaneRyder

    ZnsaneRyder Member

    What about centrifugal clutches for belt drive? I'm making my own manual belt-clutch, but if I could find a cheap clutch with a pulley, it might make things easier.

    One question, how reliable are these clutches? I always hear about them breaking on go-karts.

    I want my bike-trailer to beat the reliability of a car, so that's why I went with a clutching direct belt drive so the only item to replace is a belt. However, if the rotary clutches are good enough, I may change my mind.
  15. adamtheha

    adamtheha Member

    The clutches are fine, but the gears have been known to break. They aren't hard to replace, if you have the proper tools. I like the manual clutch, but I can't get going from a stop, which is what I really want!
  16. adamtheha

    adamtheha Member

    Ok, just received the gear puller and tried to install the clutch...don't have a @#$#% clue how the stupid thing is supposed to work. It doesn't freewheel like it's supposed to when going forward, it freewheels going BACKWARDS!!! What the heck??
    Revolutioncycles.US, I'm sorry but I'm going to have to give your product a huge thumbs down unless you really start giving the customer service! How about some instructions!
  17. adamtheha

    adamtheha Member

    Ok, so I got the clutch installed, and it works great! Still, it would be nice to have instructions. Does it have to have oil in it?
  18. brendonv

    brendonv Member

    No way do not oil a clutch, clutchs need grip, oil will make it slip. Oil in the bearings or something maybe later on but not when its new.
  19. QuadManiac

    QuadManiac Member

    Just be aware that the HT centrifugal clutch also has a one-way bearing (or freewheel) built in so when pedaling the one-way still applies torque to the engine for starting (assuming the regular clutch is engaged) but allows the engine to run at low RPMs with the clutch shoes disengaged from the drivetrain. As far as i can tell with about 50 miles on it and a Sick Bike Parts shift kit it's worked flawlessly starting the bike from a stop easily in first gear.
    Last edited: Sep 21, 2008
  20. brisbane_boy

    brisbane_boy Member

    woudent it just be easier to keep it a roll start because roll start is alot more reliable and ALOT easier.
    just a thought