Pinion Gear Keeps Coming Off

Discussion in 'Motorized Bicycle General Discussion' started by videomandw, Oct 22, 2010.

  1. videomandw

    videomandw New Member

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    hello,

    i've been having a problem with the small pinion gear that drives the larger clutch gear on my chinese two stroke. it has sheared the little key that fits between the pinion and crankshaft end three times. i've ordered new gears and new keys but it keeps doing it. i suspect it is because the slot on the end of the crank has been widened a little whenever the keys sheared. in other words, the keys fit into the crank slot kind of sloppy.

    i just put another pinion gear and key on today.l i am not expecting it to hold very long. does anyone know of a fix for this? what are my options? am i going to have to install a whole new crank because of the sloppy fit slot? if i have to install a crank, how involved is that? what are the steps i have to take?

    thank you in advance for any advice. if anyone has had their pinion gear come off several times, please let me know and what you did to remedy it.

    david
    valparaiso, in
     
  2. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    At this point I'll say that you need a new crank with a proper slot so the key doesn't knock back & forth & break off.
    But for a few dollars more you can just get a new engine. :rolleyes:
    Or, you can weld the gear back on the crank & keep riding! ;)
     
  3. reclaimer

    reclaimer New Member

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    think quick steel would be strong enough to take the slop out, or just break down and crumble? rather than epoxying it in, apply the epoxy then file it till the key fits snuglly.

    maybe find some steel slightly thicker that a woodruff key, to make your own from. leaving one end thicker to suck up the slop.
     
  4. breno

    breno New Member

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    personally i'd get foureasy's balanced crank with the stronger bearings + his crank seals.
     
  5. yendorrodney88

    yendorrodney88 New Member

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    Hi videomandw,I had this problem with mine three times now,the piece of metal which has come out of under your gear is called a woodruff key,the first two times it came out I put back in and would only last a couple of miles then it came out again,the third time i cleaned the slot and put loctite on it and so far has been fine,make sure you replace the gear straight,goodluck yendorrodney88.
     
  6. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    If it (the slot) is really wide, use some shim stock (like cutting up a feeler gauge will work) and making the key fit snugly. Also, get the key stock from Tractor Supply, Lowe's, ect. Use anything but the OEM replacement key.

    Then use Loctite.
     
  7. Mac

    Mac New Member

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    Concur with Bikeguy Joe, get a bigger key and dremmel it down to fit snuggly, bend a screwdriver to assist in installing the sprocket, kind of hold the back of it as the gear is put on, remember the gear must twist to mesh with the clutch pressure plate as it's installed, a bit tricky, if all else failsthe crank has too much runout.
     
  8. Al.Fisherman

    Al.Fisherman New Member

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    Make a key, remove large clutch gear, use red locktite, wait overnight to dry and then install.
     

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