Sprockets drive sprocket question

Discussion in 'Transmission / Drivetrain' started by jkashon, Sep 22, 2013.

  1. jkashon

    jkashon New Member

    I just got my first motorized bicycle from my brother. I do not know a whole lot about these engines, but I have been learning a lot on my own the last few days.

    Engine is 66cc skyhawk. He purchased the bike about 3-4 weeks ago from a guy in town. I know he has had his dad adjust the clutch a couple times since buying it.

    He was riding it about a week ago, pulled the clutch hit kill switch. When he went to leave he pedaled up, let go of clutch and everything turned with no resistance.

    I got it from him, I pulled the clutch cover and the clutch plate nut was off, (locking screw first thing that was missing), everything sprang out, the first few threads inside the clutch plate nut were burred smooth. I reassembled everything following the grubee instructions, and still managed to have enough thread to hold everything together correctly.

    Then still noticed no resistance to back wheel with clutch disengaged.
    I removed left side cover and the nut holding the drive sprocket on was loose, I tightened it as tight as possible by hand, reassembled everything, rolled the bike and the wheel skidded across ground.
    I Hopped on, held clutch, pedaled up to speed, released clutch and nothing. No resistance. I took apart drive sprocket cover and same situation, nut was loose again. This happened several times.

    I thought to myself it seems like it would be reverse threaded, because the direction the sprocket spins will loosen the nut everytime,but what do I know.
    So I checked the schematics and realized I'm missing another part. Grubee parts calls is a spring gasket. It goes between drive sprocket and nut.

    So my questions are
    1 - is the nut supposed to be reverse threaded or am I wrong for thinking that made more sense.
    2 - is this spring gasket really the glue that holds this nut on?
    3 - Is this supposed to be tightened with impact or torque wrench?

    Going to order a few things online soon, so trying to isolate problems and understand.

    Thanks for reading and thanks to all who reply.
    Sorry if I gave too much unnecessary information.

  2. HeadSmess

    HeadSmess Well-Known Member

    no. thats just a star washer and isnt terribly important.

    whats important is the key in the shaft, that stops the sprocket from spinning on the shaft and loosening the nut....

    without that key, you aint going anywhere :jester:

    dont despair. its pretty easy to source a new one. try a mower shop or a bearing shop. a "woodruff" key...

    theres 4 on the engine in total, if you want a sample, try pulling the clutch first.
  3. jkashon

    jkashon New Member

    Thanks headsmess for the reply. Now that I've researched and undestand keys and their relation to drives and sprockets, it makes complete sense exactly what's happening.

    Next question, do you happen to know the size of this woodruff key? I found multiple types from o'reily auto parts and there's also a cheap 80 pc. Assortment kit from harbor freight that contains 10 each of 8 different sizes for 9 bucks, thought it would be nice but not sure if it contains right size.

    Want to make sure I get right one but 4 bucks for 1 from bikeberry seems silly if I can get 10 of them for 9 bucks with the assortment package.
  4. HeadSmess

    HeadSmess Well-Known Member

    yers, the supplier does have a slight markup on a small piece of apparently insignificant steel...

    size? i dont know! i believe, dont quote me on this, it would be a 13mm radiusx2.5mm. (maybe the radius is even less, cus i have vague recollections of a 1/2" cutter being too big still...thats 12.7)

    could be 10mm.

    they come in standard sizes radius wise, but the ht seems to have two thickness which is just silly.

    unfortunately, reading back...you bought it 2nd hand already. so you wont have the puller that comes with the kits that is pretty handy about now!

    you wont remove the clutch hub by hand.

    but theres a slight chance that the magneto will pop off. they usually just slide on. sometimes, they dont slide off so easily :(

    theres a key in there. otherwise, maybe the small pinion gear is slippy loose. maybe not.

    sample now in hand, find a file, find some steel, go for it ;)

    otherwise...im sure someone could measure one.

    would be useful info.

    can you get the sprocket off? you might need to buy a puller AND a key...
  5. HeadSmess

    HeadSmess Well-Known Member

    and thinking about the sprocket...if its loose and just slides off...how is the bore/shaft?

    if the sprockets flogged in the bore, replace.

    if the shaft is flogged...

    you gunna be learning the internal structure or buying new engine shortly.

    or welding the sprocket on which fixes nearly anything instantly :)
  6. jkashon

    jkashon New Member

    Yea Unfortunately I don't have the puller tool, I need to check and see how much I can pick one up for.

    The drive sprocket does slide on and off fairly easily, but there's no play, so everything seems good there, hopefully!

    I figure probably the best route is buy the assortment pack and I will have 8 sizes to start with and 10 of each size so I can play with some if need be