Hello,
Looking at the manual for the 2006-2007 KLX250S, I see that Kawasaki used a 19/21 gear set for 6th gear. My 2009 KLX250S uses a 20/21 6th gear set. The the difference is minor but basically at any given RPM in 6th the first gen 250S is going 3MPH faster. My bike has the 351 kit, ported head, exhaust, carb… yadda yadda yadda. Anyway, any lowering of cruise RPM while retaining stock final gearing is welcome.

I’m currently in the process of splitting my cases to replace the crank due to a bad big end rod bearing, if I can confirm that the 6th gearset out of the first gen transmission will fit my bike I’d like to make the swap! Has anyone done this? Or does anyone know if the shafts out of an 06-07 will fit the 09 transmission?

I’ve done what digging I can, and so far I can confirm that both the 19/21 gear set P/N’s are different from the 20/21 gear sets. The crankcases themselves also have different P/N’s across the different generations.

Thanks in advanced for any insight or help! These motors go well back to the older 250’s and 300’s so I’m guessing they have good parts interchangability.

 

Nobody out there swapping transmissions in their KLX huh?

 

No reason, at least not for me. I rarely rev over 7k for any kind of riding, on or off road. Plenty of power in the band for me. Good luck!

 

Well that is fair enough, I did sort of word it like something someone might do for relaxation on a calm Sunday afternoon. I understand these bikes are quite reliable so luckily bottom end issues are rare when they do arise.

But since I am installing a new crank and splitting the cases isn’t optional you can probably relate to making any and all possible upgrades while I’m “in the mess” so to speak.

I actually sourced a set of 19/21 gears this evening and will give it a try, if it doesn’t work at least we’ll know for the next guy!

Lastly, I don’t make it a point to shift at redline every time, I’m actually a pretty conservative rider I feel. But I’d be lying if I said I didn’t enjoy revving the little motor out and sliding around in the dirt!

Thanks for the reply, I’ll post up my findings when I get her all torn down.

 

I'm in the process of swapping out a 06 klx 250 transmission with a Kawasaki Super Sherpa transmission after I read this thread:
​​​​​​https://www.kawasakiforums.com/forum...mission-48380/

Your going to need the whole transmission, As in the gear set along with the input and output shafts. There shouldn't be a need to replace any of the bearings. The shift forks and shift drum should be the same. If your going to do the swap you'll gain the better overdrive 6th gear with the 06-07 klx transmission. If your able to find a Super Sherpa transmission you'll get a lower 1st and 2nd gear and a better 4th, 5th and 6th. It's a wider ratio transmission in the sherpa. I think you'll like the 06-07 transmission though, just having the better overdrive 6th for reduced rpms. I always enjoy shifting into 6th gear on my 06 klx as it really drops the rpms on my 351 big bore.

 

Wow! What awesome info! I have heard of the lower 6th gear for years but I’ve never heard of the Sherpa swap. I didn’t realize the KL250G uses a similar bottom end to the KLX250S. A quick search on eBay showed 0 complete Sherpa transmissions, where do you plan to source yours from?

 

I looked on eBay for about 6 months before I found a complete Sherpa transmission. Even then I had to ask the seller which was a motorcycle salvage business to sell me just the transmission out of a bottom end. They don't show up very often on eBay, but if you want to do the Sherpa transmission swap and can wait I'm sure eventually you'll find one on eBay. The only thing the Sherpa transmission swap requires is replacing one bearing in the right case with a different Kawasaki part number, it's a 17mm ID bearing vs the 20mm that the klx transmission uses. I'm almost done putting my swapped transmission engine back together. Just got to put the top end back together and button up the right side. I put a 351 bill blue kit in it which should work extremely well with the wider ratio transmission.

I'm going to run this engine on a test stand and wiring harness before I swap it into my 06klx. I built a complete wiring harness for testing the starting circuit and ignition system.

​​​​​​Im really looking forward to trying out this swap and test run. As far as I know it's just myself and the other person that started the other thread about the Sherpa transmission swap are the only ones that have done it so far. I should have it ready to test run in a few weeks. I'll post back more when I get ready to test run it. Hope this helps.

 

I purchased a set of 19/21 gears out of a KLX300 that I'm going to try while I have everything apart. I'll report back when/if it works.

 

You are going to LOVE IT!, I can not believe how it transformed my bike. The spread is perfect.
Robert

 

Sadly, when I tore my transmission apart it was obvious that the spline pattern on the transmission shafts are different between the 300R gears I found, and my stock 250S transmission shafts.


KLX300R sixth gear on top, KLX250S sixth gear on bottom. Note the different splines