4 stroke centrifigual clutch problem

Discussion in '4-Stroke Engines' started by stowaway, Aug 18, 2007.

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  1. stowaway

    stowaway Guest

    I was riding my 4 Stroke Heng-shen bike the other day. And all of a sudden the clutch stopped engaging. So the motor revs really high and the clutch doesnt lock in and spin the sprocket. I didnt smell anything (like you'd expect in a car if you've burnt out the clutch)

    Have i burnt out my clutch? and how do i replace a clutch if it is?

  2. stowaway

    stowaway Guest


    after further investigations i noticed its not the clutch slipping. the shaft is spinnng but the sprocket that comes out of hte engine isnt.. I havent had chance to fix it yet but i assume i just have to tighten the sprocket or somethng.

    will post later how i fixed it.
  3. HoughMade

    HoughMade Guest

    Sounds like a sheared key or the bolt came out and let the key come out.
  4. salfter

    salfter New Member

    I've run into a somewhat opposite problem with the same engine...at idle, the clutch doesn't fully disengage. When coming to a stop, the engine usually stalls. After restarting, you can hear an occasional grinding noise from the gearbox and you can feel it try to move the bike. I'm thinking of tearing into the gearbox and clutch...my guess is that either the springs are a bit too weak or maybe some material needs to be sanded off the pads.
  5. stowaway

    stowaway Guest


    salfter -> I had this same problem you describe. I fixed it by adjusting the idol (the little screw that either tightens or losens the accelerator butterfly) and also adjusting fuel/air mixture screw.

    takes a bit of adjusting but i did finally get it so it idolled properly.
  6. salfter

    salfter New Member

    I've tweaked the idle...had to turn it up a bit to keep the engine from stalling out. Right now, you can hear intermittent grinding noises from the clutch if you push the bike around with the engine off. Grr.
  7. stowaway

    stowaway Guest

    salfter - i think you could try and turn the idol screw down. and adjust the fuel/air mixture screw.

    this is what i did and it seemed to work. Because if u screw the idol screw in too much. its just like pulling the accelerator. thats why it engages.

    I think i had a very similar problem. when mine was idolling it the clutch would engage for a second then disengage. so the bike would studder.
  8. stowaway

    stowaway Guest

    Back to my original question... if its a sheared key or something like that will i need to order a special part for it or will i be able to get one locally somewhere?
  9. salfter

    salfter New Member

    I just got done tearing the gearbox apart and putting it back together. It made the aforementioned grinding noises again while I was pushing it around in the garage before I started working on it. Once I had it apart, the clutch worked just fine. :?: I was able to easily spin it by hand, and it didn't show any signs of abnormal wear. I cleaned out most of the original grease (probably had too much in it from the factory), put a small amount of wheel-bearing grease on the gear teeth and bearings, and put it back together again. This time, the "push test" worked OK...no clutch dragging. A quick test ride around the parking lot turned up no problems.

    If the woodruff key in your gearbox is damaged or missing, I think you can get a replacement "off the shelf" if it's a standard size. This site has a PDF with dimensions for standard-sized woodruff keys. This site I stumbled across sells them for things like ATVs and snowblowers; I doubt they're the only ones. If there's someone near you who sells go-karts, minibikes, and things like that, they might be able to set you up with something that'll work.

    Whether it's a standard size or not is the big question. If my gearbox was still apart, it'd be no big deal to get some rough measurements off of it (don't know how good they'd be, though, as I don't have a micrometer).

    Update: Looks like what you're really looking for is a feather key, not a woodruff key...my bad. Standard dimensions for those are here, near as I can tell. Those look more like they'd be the correct shape than a woodruff key. It's a bit of a p*sser that the kit came with a somewhat complete manual for the engine, but bugger-all for the gearbox.
    Last edited: Aug 20, 2007
  10. HoughMade

    HoughMade Guest

    My local Ace Hardware has them. I would check there or at any small engine shop. They are standard items.