Sprocket Option for '95 Z50R

Discussion in 'General' started by gary1978, Jul 10, 2008.

  1. gary1978

    gary1978 New Member

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    I want to reduce the speed of our old '95 model Z50R so my grandson can start riding it. Does anyone know what largest size rear sprocket will actually fit this bike without extensively modifying the motorcyle frame, chain guards, etc.? I found a source for really large rear sprockets, but don't want to buy one if it physically won't fit. I don't think there is an electronic governor or other mechanism to slow this thing down other than changing sprockets and limiting throttle (which I've already done.)
     
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  3. reynolds_brad

    reynolds_brad Member

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    The throttles that came on XR50 and CRF50s have a screw style limiter. That might be a better option for you.
     
  4. gary1978

    gary1978 New Member

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    I already made a throttle limiter and installed it. The throttle now only opens half way. I find that if I limit it any more than that, the bike is too hard to start and keep running. And at half throttle, it will still go way to fast for my grandson. It has training wheels on it too. If there were some sort of ignition, electronic governor to limit road speed, that would be nice, but I am not aware of any such device. So gearing is the only way I know to reliably limit top speed. I just don't want to order a gear that won't mechanically fit due to interference with the swingarm, or chain guard or something else I'm not aware of. if there are other parts I need to install, such as some sort of idler, that would be fine.
     
  5. Jon440x

    Jon440x Member

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    When i worked for a dealer ship i would put a washer with a small hole in it as a restricter between the exhaust pipe and manifold ......... now this was on 2 strokes might work on a 50 ...... i am sure someone on here would know

    You could also take the top off the carb and take the slide off cut a small bit of heavy gas line and install it under the spring, so the slide will only go up till it hits the gas line .......

    just a thought

    Jon
     
  6. gary1978

    gary1978 New Member

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    That's a good idea for an easy throttle limiter. Wish I had thought of that before. But I already made a custom throttle limiter that works fine, but even at half throttle, the bike still goes too fast, which is why I am going to try for gearing now. I just want to know if anyone knows what the largest tooth count rear sprocket is that will actually fit. Stock is a 37, but will a 50 fit? What about a 60?
     
  7. Miniac

    Miniac Member

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    Perhaps you can reduce the number of teeth on the countershaft sprocket to get the same effect as increasing the teeth on the rear sprocket. I think they go as small as 12T for the old Z50A models. Perhaps there's a smaller one out there that will fit your '95. From the stock gearing, going down 1 tooth on the front is roughly the same as going up ~2-1/2 teeth on the rear. (Yeah, yeah, I know, there are no 1/2 tooth sprockets - that's just the math. :D)
    -kevin
     
  8. gary1978

    gary1978 New Member

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    You're correct. But I was already planning on changing out the front sprocket. That's easy. I've put in a throttle limiter. I'm looking for the lowest possible speed, which will be a combination of the 12T front sprocket and the largest rear sprocket that will actually fit. I'm hoping a 50T rear sprocket will fit, but I don't know if there is a mechanical interference problem that I will be unable to resolve.
    When my grandson get's more experience, I can teach him how to shift the gears, remove the throttle stop and eventually put the original sprockets back in. This bike should last him about 10 years if I do it this way.
     
  9. preventec47

    preventec47 Member

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    As far as I know the largest sprocket ever commercially offered for the Z50R is 45 teeth by JT-Sprockets
     
  10. racerx

    racerx Administrator
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    I don't really know what the limiting factors are for this bike. With CT70s, the larger the wheel sprocket, the greater the swingarm clearance. Can't recall seeing anything smaller on the engine end. Best, blind, guess is you might run into interference with the chainguard or/and flywheel cover, if you go too big at the wheel.

    I'd do some basic math. What's the stock ratio? Top speed of the early z50s was ~28mph. Figure out how far you want to reduce that (percentage) and there's your target sprocket ratio. You could have a custom sprocket made. I've seen CT70 cogs as big as 51t.

    But, before pulling the proverbial trigger try a simulated test fit, either using the existing drive chain (master link removed) or a length of clothesline to help "eyeball" the chain path with a bigger wheel sprocket.

    Final thought...I can't help but wonder how fast this machine can go in 1st gear...10 maybe 15mph will the engine screaming like a model airplane engine?
     
  11. OLD CT

    OLD CT Well-Known Member

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    I have to wonder if this bike lasted Gary's kid ten years, as this thread is 11 going on 12 YEARS OLD!
     

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