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    R1 engine in a former Geo Drakart
    #1
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    Hi All,

    Just wondering something and hopeful that some on here may be able to answer...

    I have a 2008 Geo Powered Drakart with the Drakart FNR box. Last summer engine spun a rod bearing. I came across a wrecked 2009 Yamaha R1 that had an excellent drive train. I'd like to use the R1 engine but am wondering, before I get too far into this... Does anyone know what the ideal FNR forward drive gearing ratio would be for bike engine use? What is my current gearing in there? and any idea of such difference can be minimized by a different sized driven sprocket? Engine sprocket? etc etc etc. Or is it even a worry?


    Thanks in advance!!!
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    Re: R1 engine in a former Geo Drakart
    #2
    Keeper of the Asylum K-fab's Avatar
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    As I recall the DrakFart has a ratio that's down in the 3 or 4 to 1 - which is what you want for a bike. You need to be closer to 8-10 to 1 for a CVT setup.

    Get the wheels off the ground, put it in forward and spin the wheels one turn (and be fairly accurate about the ONE turn). Count number of rotations you get from the input shaft of the trans and you'll know your numbers. You can also do it the other way around - spin the input, counting turns to get one full turn out of the wheels and you'll know the ratio.

    If you're 5:1 on down you'll be just fine with the R1.

    You'll be able to adjust the ratio a bit with the sprockets between the R1 and the input shaft.
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    Re: R1 engine in a former Geo Drakart
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    Quote Originally Posted by K-fab View Post
    As I recall the DrakFart has a ratio that's down in the 3 or 4 to 1 - which is what you want for a bike. You need to be closer to 8-10 to 1 for a CVT setup.

    Get the wheels off the ground, put it in forward and spin the wheels one turn (and be fairly accurate about the ONE turn). Count number of rotations you get from the input shaft of the trans and you'll know your numbers. You can also do it the other way around - spin the input, counting turns to get one full turn out of the wheels and you'll know the ratio.

    If you're 5:1 on down you'll be just fine with the R1.

    You'll be able to adjust the ratio a bit with the sprockets between the R1 and the input shaft.

    PERFECT! Thanks! I will do the spin today and post back here. I figured if it is anywhere close, like you say, I can fine tune (clearance providing) with sprockets. These guys for example have driven sprockets from 33 to 58 teeth... https://www.hyperracing.com/pages/pr...category=12400

    This DrakFart was actually a CVT with the Chevy Geo car engine in it. So I may be screwed anyway if its way out of range I assume.
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    Re: R1 engine in a former Geo Drakart
    #4
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    OK I just pulled engine and harness from R1. Measurements look pretty good. The R1 is 20" wide overall and the drive sprocket looks to be about 4-1/2" in from outside... which is perfect for the Drakart's available space and somewhat in alignment with the existing cvt center (which will be removed and some kind of magic made to happen at the end of the input shaft).

    On the Drakart;
    Rear tire size is 270/60 R12 (which is 25" outside diameter I think?)
    One full rotation of the tire gives 4.75 rotations of the input shaft.

    On the R1;

    Rear tire size is 190/50 ZR17 (I think that's also 25" outside diameter?)
    The existing engine sprocket size is 16 tooth.
    The existing rear sprocket size is 47 tooth.

    Any thoughts?
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    Re: R1 engine in a former Geo Drakart
    #5
    Keeper of the Asylum K-fab's Avatar
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    So tires are roughly the same - that’s good.
    gear ratios are a bit off
    16:47 is 2.9375:1
    4.75:2.9375 is 1.617:1

    If I’m doing the math correctly you’ll need a 25 tooth sprocket on the input shaft with the R1’s 16 tooth output sprocket.

    Somewhere there’s a sticky that does all the gear ratios - I’m a CVT guy so I’ve never used it.

    It’s definitely a doable setup.

    One thing to consider: the R1 will run 160 - you don’t want to be able to go that fast in a buggy.
    100 in a Drak would be the absolute limit I’d consider. I’d gear for acceleration versus top end.
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    Re: R1 engine in a former Geo Drakart
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    Awesome, so If I fudge the input shaft sprocket up even a few more teeth than 25 then I am at least erring on the side of more low end torque rather than a 160mph+ minibuggy?

    Continued Thanks K! You make sense.
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    Re: R1 engine in a former Geo Drakart
    #7
    Keeper of the Asylum K-fab's Avatar
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    Yeah, you’ve got the right idea.

    I'm hoping one of the bike powered guys comes in and comments and that I did that ratio thing right.
    Last edited by K-fab; 06-08-2018 at 07:25 PM.
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    Re: R1 engine in a former Geo Drakart
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    Looks good, the larger sprocket on the trans will lower your top end which is what you want and will allow you to run more chain length and help to keep the chain cooler.
    Are you going to have that conversion done and bring it out to Glamis by Thanksgiving
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    Re: R1 engine in a former Geo Drakart
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    Thank you both for the input. And that's great initial news to me. I was worried about hitting a brick wall in trying to re-gear the FNR somehow.

    Ha! That would be awesome! You know I dig watching you all rip up the dunes but, you are right, I need to get this one on out there. I'm on my KTM in Big Bear and Arrowhead several days next month (6th through 20th). We have a silver lake trip coming up after that and I am trying to have the Drakart running again by then. So if that happens, and it runs right, man I would be all over driving it out to Glamis for one of the holidays anyway.

    Tonite trying to figure out how to get the driven Artic Cat CVT off of the Drakart FNR input shaft. It's really stuck on there.
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    Re: R1 engine in a former Geo Drakart
    #10
    Keeper of the Asylum K-fab's Avatar
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    Pull the clutch apart (careful of that spring) put a little heat to it and whack it on the back side. It’ll come off.

    I’ve fought my fair share of them this way.
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