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Discussion Starter · #1 ·
I've seen a couple other threads on installing 15 tooth front sprockets, but thought I'd share some pictures of installing mine to help out.

First off - I never saw a consensus on which JT part # was correct for the 300. I looked at JT's drawing on their website, and ordered the JTF1539-15.After removing the factory 14T sprocket from the 300 I can confirm the JTF1539 has the same offset as the factory sprocket. I'm not saying that some of the other part #'s floating around out there won't work, but the 1539 puts the chain right where the factory had it.




I started by removing the shift linkage. note that the factory was nice enough to make an index mark for re-aligning the shifter for assembly.




Removed the black plastic sprocket cover




Followed by the speedometer pick-up (marked in red) and bracket (marked in green).




Using a chisel and hammer I flattened the washer locking the CS nut (the big one) in place, being careful so I could re-use it.

I used a pneumatic impact wrench to remove the CS nut. I'd imagine a socket and enough leverage would work also, but you would need to jam something in the rear wheel to keep it from just turning over. With the CS nut off, I loosened the chain and dropped it off of the rear sprocket, giving me enough slack to remove the front sprocket. If you are not familiar with checking and adjusting chain tension - get out your owners manual that came with the bike - it's in there and is something that should be done regularly!

The new sprocket slipped on easily and I reversed the procedure to button it back up.







I am curious to see how far off the speedometer is after this... a speedoDRD is easy enough to install but would change this from a $20 mod to a $100 one.

Anyways - I hope some of these pics help those of you contemplating the switch!
 

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I love your posts!!!

So detailed and pictures are clear and understandable.

Really appreciate these threads.

Sent from my R800x using Motorcycle.com Free App
 

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nice post.... my biggest concern with doing this is the rear wheel, and getting it lined back up properly. I already have my sprocket, just need to get the big ass socket as well....

what are the size of the sockets needed to take of the rear axle and the CS nut???
 

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Discussion Starter · #12 ·
Ben - the purpose of adding a tooth on the front sprocket is to lower the engine speed in relation to wheel speed.


Krispy - I used a crescent wrench on the axle nut, so I don't know what size it is.

Instructions for alignment are in your owners manual, it's no different than adjusting your chain slack. You're just starting out with the adjusters backed all the way out - just turn the adjustment nuts the same amount of times on both sides. Here's a picture of the adjuster backed off and the axle nut loose. just shove the wheel forward and the chain will have enough slack to drop off of the sprocket.





I used a 1 1/16" impact socket on the CS nut, I believe that would translate to a 27mm in metric.
 

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Today I just when on the highway to see how much my speedo is off.... It is dead on up to 85mph with the basic front sprocket right now. And I only got to 85mph becuz I had to slow down becuz of my exit I had to get off at. Wondering now when I do the step up how much will it be off


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I confirmed the speedo with the +1 on GPS as correct up to 80 MPH. Others have found the stock geared speedo off 5-7 MPH at 100 MPH.
 

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Discussion Starter · #16 ·
If the speedometer is measuring front sprocket revolutions wouldn't it be off 7% after adding a tooth?
Yes, but most bikes are not accurate from the factory. Depending on whether the sprocket change goes toward correcting or exaggerating the factory error would determine the need for a speedoDRD. It sounds like in the case of the 300 it goes toward correction. It has been raining here for a week straight so I haven't been willing to go ride the wife's new bike and get it filthy to find out first hand. :)

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Thanks for all the info. Gotta keep this thread so I can use it to do mine.
 

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I did this mod and while I was at it I took the slop out of the shifter. I pulled the shifter off of the pivot, greased everything up good and used a showa shock valve disk/washers to shim the slop out of the pivot. Makes for crisper shifts. I did not measure anything just used what I had and trial and error to get the correct thickness. I had a bunch of left overs from the gold valve kit I put in my cr450 shock in a tool box and they had the correct ID to fit over the shaft.
 
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