KTM 640 Adventure-17/42T gearing question

It's generally reckoned to have your sprockets in an ODD/EVEN ratio or EVEN/ODD for that matter, to get better life.

I'm thinking more along the lines of the chain having a larger radius at the bends which is less stress full... Also with 17/45 the chain ends up farther away from the swingarm pivot point and therefore has less contact with the rub blocks...

Very true.

After seeing my 47 teeth r/s has lost 7 teeth this last week :eek1, I followed your advice and ordered a rear steel KTM sprocket finally with 45 teeth. At 29€ it's half the price of the powerparts one, and I wouldn't say the latter would last as much. As for the c/s, as wasn't sure what to choose, I ordered a set of 15, 16 and 17 teeth to try different options. For my offroad use I think I'll stay with the 15/45, and when planning longer onroad trips I can quickly change it for a taller one. As for the chain, I decided to go for the DID Z-ring, not too expensive at 90€ and apparently giving fairly good results.

. At last I found time to get the new oem 17 c/s, 45 steel rear and RK chain fitted. The 17 c/s does fit without any issue, I didn't even have to remove the case guard, a straight-on fit. Well advised - thanks - I changed the nut/washer as well.
My previous ratio was 16/48, which wasn't bad offroad but clearly too short on pavement, even on twisty roads I seldom used anything else than 5th gear. First gear seems enough to get into trouble and out of it when on my usual playground and for the real tight single track I can fit the 15 c/s. Great for the 80% off 20% on I normally do.
I'm happy to have found a street friendly bike -er ... those vibrations .. -:eek1, without apparently losing too much of the real offroad fun

I ran 17/42 for while as my street setup but have switched to 17/38 as my freeway and commuter setup, between that and bar end weights the bike has smoothed out on the road.
15/42 is for dirt, going to try 15/45 soon.

A question to confirm before I order a 15t.

I'm currently running stock 16/42 but have a 45 laying around that I want to throw on for some woods work/fun this fall.

It seems the 16/45 will not work.

Will a 15/45 work with standard chain length?

I replaced the drive chain & sprockets last week with a 14/40 combo (steel). It was pretty nice off road, but buzzed at 55mph down the freeway. I put my stock 16T on the front to match what came with the bike. 16/40 works okay for dirt with no added load. I'd like to try a 17T up front but I don't have the chain length.

Get some masterlinks and add a link.

b

Those of you that have gone to a 17 tooth front counter sprocket... Is this a good choice?

http://www.ebay.com/itm/JT-SPROCKET...ubmodel:Adventure&hash=item2edec52612&vxp=mtr

Which rear sprocket?

b

Factory issued 42.

This sprocket. No, stick with OEM for the front sprockets. You can pick any flavor for the rears though.

The front OEM sprockets are a slight bit thicker than the aftermarket brands. Why is this important you may wonder? The way the front sprocket is mounted, coupled with the counter shaft sleeve with the machined inside lip and O-Ring compresses and seals against oil leaks on the counter shaft.

As the countershaft sprocket nut is tightened that little O-Ring which fits over the counter shaft is compressed against the inner race of the countershaft bearing.

The proper amount of compression on that little O-Ring is influenced by the correct thickness of counter sprocket. Aftermarket CS's are 0.015" (if I remember correctly) thinner than OEM. Since they are thinner that little O-Ring doesn't get compressed enough to create a proper seal and oil leaks will rear their ugly head.

I did like the 17/42 combinado on my 640A for general roadwork. Too tall for single and two-track IMHO.

Dirty

Thank you very much.

I searched but couldnt find a part number for the OEM sprocket. Called my local KTM parts guy and he couldnt find one either. Any one know what the part # is?

This is all true in my experience, worn out couple of 17T sprockets. In the woods stay in the power band.

b

Have him look up the OEM sprocket for the Duke or Duke II, that should be the one you're looking for.

Agree with the others, 16/45 is what I run for dual sport gearing. 17/42 is just street, in my opinion.

Counter Shaft sprocket
17 tooth -580 33 029 017
16 tooth- 580 33 029 016
15 tooth- 580 33 029 015
Rear Wheel sprocket steel
42 tooth- 582 10 051 042
45 tooth- 582 10 051 045


I usually run 17/45 in the KTM steel sprockets, these give the longest life coupled with a DID chain...
At the moment I am running 17/44 with a JT rear sprocket which has given ok service life...

fixed

KTM Engine Sprocket 17 T #58033029017

Save some grinding KTM Chain Dampersheet 17 T #58730047100

Much obliged gentlemen.