KTM LC4 revalving and rebuilding the shock absorber

Going sideways

The shock absorber is universal among LC4 except for the Duke which looks identical but have some different parts. It is a pretty standard piggyback design from WP with a 14mm shock shaft and 46mm piston size.  The shock is available from the factory in different versions with travel and internal shim stack adapted to the intended use.

SMC shocks are shorter and have stiffer valving. SXC shocks are the tallest and ADV in the middle. The info of stroke and length comes from the suspension settings sheet and claimed suspension travel from the owners manual.

The suspension travel and length is dictated by an internal rebound spacer. If you are short you add more spacers thereby lowering the ride at the cost of suspension travel, that is my preferred way of lowering the bike compared to Koubalink etc which makes the suspension softer and less progressive. If you are serious about offroading and got long legs increasing travel to the max is a must. SMC and ADV shocks can easily have a spacer removed to increase the travel to SXC length. This is especially important if you extend the forks as i outlined in my last blog post. 

The shock in the picture is a 2004 SMC shock which have 3 spacers, removing two of them gives an extra 15mm of suspension travel.

Springs:

The shock spring is a 59mm id straight rate and 260mm long. WP springs are marked XX-YYY where the first number is the spring rate in N/mm, the second 3 digit number is the spring length in mm. 640ADV and SMC uses mostly 70N/mm, SXC have 63N/mm as standard, the stiffest spring rate available from WP is 85N/mm. 625SXC/SMC have a claimed weight without fuel of 132kg and the 640ADV 158kg, that is even before 25L of fuel. In the light of that weight handicap it is easy to see that the 640ADV is severely undersprung even with the 75kg recommended rider weight. 

Even the stiffest WP spring is usually too soft if you are heavy or carry some luggage. However there are manufacturers of custom wound springs that can be made in any rate, Cannon racecraft or Slavens Racing are good ones. If you  are  located in Sweden or Europe i stock some springs at a competitive price.
Slavens offers a spring chart which is a rough guide to your recommended spring rate, note that it is for the enduro models not the heavy Adventure. The only way to know which spring is right for you is to measure static and dynamic SAG of your bike with the load you usually run.

Valving
The original shock valving can be found in this spreadsheet i have compiled. Looking at the valving it is strange that the relatively heavy 640 ADV have softer stacks compared to both 625 SXC and SMC. That is however also my impression from the shock, it is too soft for anything more demanding then road use. In the sheet you can also find valving from the 660Rally back in 2001 when it used the same configuration as the ADV shock, the shim stack is about 3 times as hard. I have also included the shim stack from my own shock absorber which i use as a base for the revalves and rebuilds i perform.Finding the right stack just for you is the paid service....