Noises and Sprocket ratio for KTM 400 exc Racing (2006)

[PaulMcLaughlin]

Hi All,
The 400 exc was making some worrying clunking noises around the rear end. Chain was within spec and correctly adjusted and the sprockets didn't look particularly worn but I replaced them to be on the safe side = bike it transformed from a knocking, grabby, tiring handful to a smooth, controllable pleasure to ride. Lesson learned.

I was told by the supplier that the recommended sizes were 15:45 for a 2003-2011 400 exc Racing which is very different from the 13:50 I removed. Some investigation JTSprockets (http://www.jtsprockets.com/catalogue/model/4226) and the KTM handbook that came with the bike confirmed this so I spent my £70.

However, a 15 tooth front simply won't fit without cutting the chain slider and removing the clutch actuator guard which is obviously wrong.

U.S. and other specific-model 400 exc's run with a 14:50 ratio which Chris Elderfiels in Farnahm http://www.elderfields.co.uk/ had in stock. They fit perfectly and feel just right.

Does anyone know what the issue is here; why is 15:45 put forward as an option by KTM and sprocket manufacturers for those years when it simply won't fit? Would they maybe be for the later EX4 engine (08-11?) I'm in the process of trying to get a refund on these sprockets so any insight would be appreciated.

All the best,
Paul Mc

[Stewie]

Not being in KTM's R & D department this is just MHO, the bikes are not fitted with the clutch saver as stock and sliders may well have been changed to an after market one, but that said 15 on the front and 45 rear is leaning towards road gearing, 14 front is as big as I go.

[PaulMcLaughlin]

Cheers Stewie, I didn't know about the clutch saver not being standard. It is KTM branded so I figured it was original or designed to fit the standard configuration. I believe the chain slider is original but it's certainly not very thick; maybe 5mm. It'd have to be about 1-2mm thick to accomodate the 15 tooth.

I guess it's possible that without a clutch saver and with a wafer-thin slider the sprockets could fit but as you say the gearing then is certainly out of whack with the off-road focus of the bike

Anyway the seller will take them back if I clean them up so I might not be much out of pocket.

[langley beta]

Paul, I run a Beta 400RR which uses a KTM RFS engine the sprockets are 14X50 and this ratio is perfect for green lane work and on road. Ron

[PaulMcLaughlin]

Hi Ron,
Yep 14:50 is very usable, noticeably less aggressive than the 13:50 I replaced.

[newsh]

As well as being road gearing 15-45 is also an exact division by 3 so will wear quickly and tend to hunt.
I'd have to check but I think I used to run 14-48 on the 450, it tames the bike down a bit, is easier to stay out of the power (it was my first off-road bike) and makes the roadwork easier.