HELP! Grubee drive sprocket failure

Discussion in '4-Stroke Engines' started by Irish John, Aug 21, 2008.

  1. Irish John

    Irish John Guest

    I lost drive to my sprocket last night and thought I'd snapped a key by engaging the clutch at about mid revs. Both keys are intact as can be seen from the pics but I think the problem is in the freewheel sprocket itself. When I turn the sprocket backwards while holding the drive shaft the sprocket will turn against the drife shaft when it should be totally connected. I wonder how I can get the freewheel sprocket off. I've taken the bolt off the end of it and I don't know how to get it off. Also don't know how to get the final drive shaft out to inspect it although it all looks OK.
    Can anyone help me here?
     

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    Last edited by a moderator: Aug 21, 2008

  2. Irish John

    Irish John Guest

    Found a key in the freewheel sprocket

    I managed to get the sprocket off the shaft with a 3 jawed gear puller and there is a key in there and I think it's sheered off. Maybe it's just a wedge and not a key but I think if you look at the pics you can see a similar shape in the shaft where it probably sheered off. The key that I took out of the sprocket tself has a curved bottom that correlates exactly with the shaft so I think it has sheered. very clean sheer though don't you think. I'm really interested in anyones expertise here but I think I'll try to punch the remaining bit of key out of the shaft and if no luck then drilling it out in bits. Hopefully I can make a key to fit it by milling away at a pice of engine key until I get it down to size. The engine key is so much bigger but I have lengths of that to play with. All this filing is probably bad for the temper of the steel as well as the temper of the Irishman. Has anyone any experience with these sprockets?
     

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  3. Irish John

    Irish John Guest

    That was a key that you can see in the shaft. I've punched it out and am making a new key for the sprocket from a piece of 1/8" key steel. It's a very precise shape with rounded ends. Anyway I've found out a bit about the freewheel sprocket & shaft so that's no harm.
    There are pictures of the keyway and new key on my Honda\Schwinn thread:
    http://www.motoredbikes.com/showthread.php?p=151642#post151642
    Isn't it good to know that the key to snap first when you drop the clutch at too high revs is the smallest of the three keys - the 1/8" drive sprocket key as opposed to the 3/16" engine shaft key or the gear engager shaft key which looks like it's 3/16" too?
     
    Last edited by a moderator: Aug 22, 2008
  4. nsideus

    nsideus Guest

    Irish, I have sheared a couple of these keys and done the same as you and made my own. The final drive sprocket is the 1st place I go to when drive is lost.
     
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