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51815 Views 207 Replies 46 Participants Last post by  JTACKM
I love the new wider ratio trans, much better than the old 250 in both spread and shift action precision. However, the gearing on the 300 is very low in first, and I was using second gear most of the time from a dead stop. Even with a passenger it was better than first which was more noise than action IMO.

On went a 2008-12 15t counter shaft sprocket, fit perfectly and suddenly I have a useable first gear! Nice mod, and I'm a guy who runs super short gears on everything I own. My Mustang has 4.56s and my KTM 950 SMR had a -2 front CS so I like my peppy gearing.

Another +, I think the speedo will be closer to actual speed now, stock it runs higher than actual speed. I'll verify that with a GPS ASAP but so far I'm convinced it is actually dong the speed it is reading.
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Do you know if the 08-12 rear sprocket is a bolt up also? I would love to change my sprockets, so if I can just order the old 250 stuff that would be great. I'm glad it runs a 520 chain from the factory, that was the first thing I did to my R6 was a 520 conversion.

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I have a 250R +1 front sprocket in my tool box, how long does the install take?

Dont forget a +1 gets you a higher top speed as well :)
I doubt it will pull the taller gearing to redline in 6th but it might? It will lower RPMs at all road speeds and it still pulls it well with the great midrange power/torque so why not?

It took all of 25 minutes. Lets see how much I can recall to help out with the swap.

You need a 8mm socket/t-handle to remove the sprocket cover and the speedo pick up beneath it, set the speedo pick up aside on top of the engine case and bend open the thin wire strap, watch the second wire there too, just don't pull on it and watch the orientation for assembly.

Mark the shifter slot/shaft with marker so you can easily line it back up and a 10mm wrench gets that out of the way.

You need a hammer and a flat, dull screwdriver to open up the bent nut retainer on the CS sprocket.

A 12 and 14mm wrench to loosen the axle adjusters and a 1-1/16 box wrench will work for the axle nut after you pull the cotter pin. That might be a 27mm nut there but not 100% sure.

I think I used a 1-1/16 deep socket on the CS nut and I tapped it off with an impact gun, 1/2 drive pneumatic.

Once everything is loose, push the rear wheel forward and the sprocket can be extracted from the now loose chain and shaft.

Slip in the 15t, it fits but the splines can be a PITA. Add retainer washer and nut being sure the splines are engaged.

Adjust chain to proper tension, tighten wheel. I gave the CS nut a few taps with the impact gun, you don't need to murder it and I'm sure there is a torque spec but i do alot of these and the lock washer gets bent over to retain it too. A large slip lock plier makes this easy, simply engage the lip and a flat on the opposite side of the nut and squeeze it flat along the nut using a new, fresh edge of the washer so it doesn't weaken and break off.

Reassemble the speedo sensor, recrimp the wire strap and the replace the shifter/cover.

Go ride it and tell me it isn't how the bike should be delivered! :D
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There, I think I got all my typos corrected! I did the best I could from memory on the nut sizes, hope I got the 1-1/16th right for the CS nut, 100% sure on the others.
What brand did you get? I think the one I have is JT sprocket.
Ok, I will try to install it this weekend, I am gonna rip the bike apart to prep for my projector headlight install :)

The sprocket has a small lip on it, does that go to the inside or outside face, or is it obvious once you take it apart?
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Inside as I recollect. Just look at the one coming off, it was obvious.

The replacement I got had two threaded bolt holes in it that you won't use. I did a quick 15 miles on it before it got too dark, cold and "deer-y" outside, friggin rut season! Totally transforms first gear and I'm pressed to even feel it affect the other cogs. I'm very gearing sensetive so that shocked me.
what model number did you get of JT? I see several that supposedly fit the 2012 ninja 250... that are all 15t... lol
Sorry, don't have a pn handy. The only difference should be those threaded holes I described. Some may have them, some don't. Otherwise they should be the same if the numbers are correct.
Scratch that! pn # jtf516.15, I sw the package in the bin in the garage.
Crap... I just ordered JT Sprockets JTF1539.15 15T Steel Front Sprocket....

Amazon said it would fit my bike, and that the one that the JT site told em to use. at least I think that how I interpreted it =(

Any ideas if this one'll work? or what the difference is?

Top speed in each gear at the rev limiter;

1st=37 MPH

I've been to 100 in both 5th & 6th, gotta find a spot to stretch it to the top of the speedo soon.

I'm still running a +1 CS which seems to have correctted the high reading speedo. (edit) GPS confirmed!!! Speedo is right on the $ every 10 MPH up to 70 MPH.
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Hey guys what's the standard number of teeth on front
question guys... I am still confused... I ordered a JT1539 15t front sprocket. Manufacturer says it'll fit... on their web site... But on here it looks like everyone got the 565..?

the 565 is meant for the 650 engines far as i can tell. heres a list of applications.

and heres the one for the 250

and the 250r

so what did you install? did it fit? and am I wrong in the part I ordered before I start ripping my bike apart?
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I dont know my part number but its for a 250R haha.. I bought it for my 250R and never installed it, and it fits on the 300 :)
So? Did ya ride it yet?
Me? Yes I did, not even noticeable power wise, but a nice difference in RPM :)
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