06 kx250f transmission problem

Ive recently been having problems changing gear. Usually hitting a false neutral but the when out riding a few days ago the bike made a horrible crunching sound and the engine locked up and the gear lever wouldnt move. I managed to unjam it by kicking the gear lever. When i got it home i started it on the stand without any problems but when clicked into 4th it would lock up again? Ive got the gearbox apart and cant see any teeth missing but theres a few chips and marks on a few of the gears and one of the selector forks is heavily worn. what could cause the engine to lock up like that? Also would i be able to fit an 07 transmission (gears & shafts & selector forks) in my 06 gearbox?

It's probably due to a bent shift fork.

Yea an 07 trans will fit

Agree on the bent shift fork. I have had that happen twice on an 06 KX250F. Carefully inspect all components for wear marks including the shift mechanism outside the case. The second time I replaced anything and everything that was even slightly worn. Its been good for about 40 hrs now. Still going strong. :bonk:

Carefully inspect the shift drum and the mechanism too.

-07 had a stronger gearbox I believe...

Thanks for your help guys, there doesnt appear to be any damage to the shift drum and mechanism so have bought the shift forks, gears and shafts from an 07 model. Will get them fitted and hopefully all will be well!

I have a problem with my 08 where on a start it doesnt want to shift up. I start in second then its really hard to get 3rd even letting off and with the clutch. Anywhere else it shifts just fine any suggestions? It has low hours on it so I don't believe anything is worn out.

Welcome to the KXF shifting club!

On a serious note, they are hard to shift when they are under full load. Either shift a little bit later, when the revs are higher and the load is less, or practice using the clutch at just the right time.

The -09 shifts a little bit better. I never miss shifts on the start. Well, maybe once:smirk:

alright well it makes me feel a little better knowing it's not just me haha. thanks.

Got the 07 transmission parts today, fitted them into the casing along with the shift forks and shift drum and it doesnt work? When i try to turn the gears they stop at a certain point, and the shift drum doesnt want to turn in some places. I swapped the 07 parts back to the 06 parts and it works fine? Ive had a look at both 07 and 06 diagrams in the manual and the arrangement of the gears and shift forks seems different, is the 07 shift drum different to the 06 shift drum?

This is what I found:

An all-new 5-speed transmission with thicker gears offers improved shifting and increased durability.

New shift drum with modifications to the ratchet mechanism and a new ball Bearing shift lever improve shift feel"It sounds like it´s quite a bit different.

Maybe you can´t just switch out some parts. Maybe you need all of them at once.

Dam! Will buy an 07 shift drum and hopefully thats all I need, if not I'll keep buying 07 parts till it works! :bonk:

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