Just how wide is a Wide Pedal Crank?

Discussion in 'Mounting Techniques for Bicycle Motors' started by cachehiker, Jul 11, 2008.

  1. cachehiker

    cachehiker New Member

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    The title says it all.

    I'm looking at mounting a 4-stroke with a centrifugal clutch in the frame. I assume the wide pedal cranks are provided to ensure the crankarms miss the sides of the engine. Anyway, has anybody actually measured the Q-factor of these cranks?

    I'm looking to motorize a ten year old GT with a standard UN-72 square taper bottom bracket. It's a triple crank that would be converted to a single ring in the front. I already have a much wider bottom bracket that I could use to put the crank arms out another half inch or more but I need to know how wide is wide enough.
     
  2. Scotty

    Scotty New Member

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    I guess it depends on the design and engine placement. I run a wide bb, 127mm, but this doesnt clear the motor. I placed the motor forward and higher so the cranks clear. Most frames dont have room for the motor in this space so you may need an x/large frame or custom made.
     
  3. cachehiker

    cachehiker New Member

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    If 127mm doesn't clear the motor for you, I'm pretty sure I won't make it either. It looks like I can fit a 48cc 2-stroke in there if I can find a clutch actuating mechanism that I like. I don't want two levers on the left side and since I'm a cyclist first, I don't want to get used to braking solely from the right.
     
  4. ocscully

    ocscully New Member

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    The Optional Wide 3-piece crankset offered from GRUBEE and other vendors are designed to clear the Honda GXH50/Clone motor and its attendent gearbox. This set-up is 9.5 inches wide. The wide crankset is designed to clear this with what ever square tapered BB your bike has for its existing crank set. The wide crankset is also a single 44t sprocket. Just changing to a longer spindle isn't even close and would cause chain line problems for the pedal side as well if you could find a spindle long enough.

    ocscully

    Just
     
  5. jimraysr

    jimraysr New Member

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    My Honda GXH50 plus a GruBee gear box is 232mm (9 1/8") at its widest point. Below the bulge for the bearings it is only 222mm (8.75")

    My three piece peddle set clears 229mm (9")

    The one piece that I could not use is 225mm (8.75")

    I just installed the wide cranks yesterday on the 38mm (1.5”) factory lower bracket. The one piece crank requires a 51mm (2”) lower bracket to fit through and use the bearings that come with it.

    The attachment is a picture of the new wide cranks. Jim
     

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  6. MotorbikeMike

    MotorbikeMike Dealer

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    Cachehiker, contact me if you like, I have Rotary clutch handles (match the old-style throttle)

    Mike
     
  7. Dan

    Dan Staff
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    Hi jimraysr. Where did you get your cranks?
     
  8. jimraysr

    jimraysr New Member

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    Spooky Tooth. Think they were $20. Just the two cranks that fit on the square spindle of the lower bracker. The type that have internal threads for a removal tool and are retained by a bolt into the spindle. Good Luck.

    Trying to find these parts often seems to be the most time consuming part. Guess I am going to have to buy a minil beer keg and make my own round tank to go behind the seat?

    Jim
     
  9. Dan

    Dan Staff
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    Thanks Jim.

    Your right about the time used for just finding all the stuff that will play nice together. Can be maddening.:eek:
     
  10. HeresPaco

    HeresPaco New Member

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    Hi Jim, Nice pedal cranks you have.
    I don't see these on Spooky Tooth's online parts list. (only the one piece crank set) Did you have to call Spooky's for them?
     
  11. jimraysr

    jimraysr New Member

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    Yes, I did call him to get them. May have been ones left over for a 4 stroke build? Anyway he seemed pretty down on the GruBee 4 stroke kits back then (18 months ago) as he like a lot of dealers has gotten stung with transmission / clutch problems. He didn't say anything directly about them, but was very hesitant to sell me a transmission, fearing a kickback? I got what I paid far and knew the possible problems.

    The transmission I got from him, like the one in my kit, the clutch has the wrong size keyway, which didn't match the engine or the idler bushing? eventually I got the proper one from Bicycle Engine. So I have a spare transmission and two clutches. when I need a clutch, I will mill the key slot wider or step a key to fit it? No biggie.

    Anyway after seeing the GruBee belt drive, I am glad I have a transmission for a future build.

    Back to your question, maybe he has an other set of wide cranks and the sprocket?

    Jim
     
  12. HeresPaco

    HeresPaco New Member

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    Thanks for the info Jim.

    I have a Walmart Schwinn Point Beach 7 speed with a ZoomBikes 66cc 2 stroke and a Sick Bike Parts shifter kit on it. I want to use a pull starter and need wider crank arms for that.

    I just ordered a pair from "GasBikeShop - RuiHong Enterprises Ltd." I'll find out how well that outfit does business soon enough. They were $28 with the shipping.
     
  13. jimraysr

    jimraysr New Member

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    I got a pull start for the 48cc that I was given. Took a little juggling with washers and nuts to get the moving part to clear the mag frame, but now, it looks good. The only place I found the pull start was Zoombicycles. They suggest changing the China rope. Other engine parts I needed came from Gasbike.net / KingMotorBikes (same outfit.) They both acted like business, businesses and gave good service.

    Good you found the cranks. I looked for several weeks.

    Jim
     
    #13 jimraysr, Oct 20, 2009
    Last edited: Oct 20, 2009

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