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| 250cc and Above Engine Tech Technical Discussion Forum for 250cc and up Engines |
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#1
07-26-2012, 07:14 AM
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gearing/sprockets
Hey guys, first of all I'm a newbie here. I recently bought an unfinished project and have been fixing/adjusting things as I go. Originally it was some sort of Chinese twin seater with a 250cc. But now the frame has been extended, plus it has a motorbike engine in it, from a Honda VFR 750 road bike, 6 speed. Ive managed to get all my front end sorted, me next problem is utilizing its power/potential. I'm no expert on any of this stuff so bear with me! I reckon its geared way too much toward low end grunt. Basically don't use first at all, take off in second with clutch, then can just flick through the rest of the gears without clutch. Problem is it revs out way too early. Pretty much only use 6th gear, the way its set up at the moment it feels like its still pulling and should have another 3 gears! I figure it has to be to do with the sizes of the sprockets. Now Ive read a few posts about people having a 4:1 ratio as in say 15 teeth on the front and 60 on the back then adjusting from there.. Trouble is mine is already at 1:1, 17 teeth each one.. Plus it has a diff with forward, neutral and reverse, could the diff be the prob?. I was thinking of getting a smaller cog by one or two teeth at the back but I'm not sure! Any help/hints would be greatly appreciated! Also pretty sure that the same model bike runs a 16 and 43 if that might help
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#2
07-26-2012, 07:47 AM
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Look at the gear box and see kind it is so you can find out ratio it is.Most (rpm,jefco and ones like that)are 4:1 - 5:1.
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http://www.youtube.com/watch?v=IUgir...ature=g-t=2668 FABRICATION ITS HARDER THAN YOU THINK |
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#4
07-26-2012, 08:31 AM
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Post some pictures of your setup. I built a mini-buggy with a VFR750. I used the stock sprocket on the engine and a 60 tooth on the rear. It was geared too high. 1st gear was barely able to get it rolling without some good throttle. Most of the time I rode around the trails in third and it was great.
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#5
07-26-2012, 12:26 PM
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Welcome-again post some pic's so we can see what you have,
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#6
07-27-2012, 05:33 AM
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They arent the best photos, but anyway. you won't be able to see the drive sprocket, and you'll notice Ive removed the tensioner sprocket already. Ive decided I'm gonna drop the diff and prob get a 45 or 50 tooth sprocket and weld it to the rear axel. Thoughts?
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#7
07-27-2012, 11:09 AM
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Interesting modification!!!! I take it you have no idea who makes the differential rearend? Just so I'm covering the bases- does reverse have the same gear ratio?
From what I can see it appears putting a "smaller" input sprocket on the differential would help-with the size of the input shaft you might be able to get down to a 13tooth- Your comment about dropping the differential- Is the axle solid & splined at the differential box?Is so then is your idea to add a bearing carrier where the differential was and just come up with a sprocket carrier? |
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#8
07-31-2012, 07:07 AM
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Cheers for the input guys. Yeah I can't work out the make of the differential, and it does have the same ratio. I have since taken the diff out, and actually took it apart and am just going to use the bearing carrier from inside the diff and connect my two axles.
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#9
07-31-2012, 07:12 AM
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I stumbled accross this setup in the image below, may have to try something similar with the seperate axles as without the diff the distance would be too great for the chain, plus it wont physically work with out further serious modification. I'm thinking that with out the diff I should be able to put a 45 or 48 tooth sprocket at the back now too.
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