This guide is for the WP 4860 MXMA (MX Multi Adjuster 2003) forks on my 2003 KTM 640 Adventure; also know as WP 48mm USD forks
. This is all I have; if folks have information on other LC4 WP forks then add your info to this thread.
USER BEWARE: I am not a suspension expert! The blame lays with you alone for choosing to follow the advice of some guy off the internet!
I did get quite a bit of help from a couple of good LC4 suspension tuners and I will pass along the info they shared with me that should help most DIY maintenance folks. Many have been relying on neduro’s Fork Oil Change
thread, which is not on WP forks. I found out there are some WP issues, so I have herded them into one thread to help folks out.
Some background info
48mm refers to the diameter of the fork tubes, not the springs. The stock spring for this model of fork is: 43mm OD x 485mm L. Some posts on ADV said these forks can handle up to 510mm L if you remove all the preload spacers. My tuner set the preload so I can’t help you any more than passing along his note that no two spring are alike, so the preload can be different in each leg. If you don’t buy that here is what Race Tech says:
Originally Posted by RT website
Most manufacturers hold rates within +/-5%, this means a spring marked 5.0 kg/mm could be a 4.75 or even 5.25. (A spring marked 5.0 could be the same rate as one marked 5.4!)
FWIW: the inner diameter of the spring also matters (I think on this model it is ~33mm ID) because it should hug the spring guide. Some shops said the spring guide could be shaved a bit to help fit a spring with a smaller ID, but I have no verification on that tip.
And ONE BIG FYI:
the manual is flat WRONG about the amount of oil you will need to fill your forks.
The manual says the capacity is “ca 420 ccm” (ca means “about” and ccm is cubic centimeters - you might call them CCs in your Camaro - which are the same as milliliters or ml... crazy metric system). That amount is less than one standard bottle per leg, but it turns out you might need as much as 600 ccm per leg depending on how high you set your oil height! That’s almost 50% more than their “capacity” spec… so get yourself three standard bottles or at least 1200 ml/cc(m) right from the get to save you from those annoying repeat trips to the store when you're trying to close up your forks.
OK, shall we get on with it? No! Tough crowd… well, let me give you some additional info
that you will need to use this guide. Here is a thread from KTM Talk that has pictures and descriptions of all the WP fork parts:
That will help you understand what you are looking at and give you some idea of how they go together. What I call the fork parts is some mix of those used in that thread and the WP workshop manual. I had a hard time finding the correct version of the 4860 manual for download, but this one will work:
one version of the WP 4860 Workshop Manual
And here is another site with some WP downloads: Husaberg.org
I also found this download helpful: a WP fork service one page guide
. Those will help, but only if you read through them a few times. No, not skim and look at the pictures – study them. You will know you are done when my guide makes sense. And if you don't see a picture below, chances are you will find one in those resources. Now can we get on with it?