ADVrider (
-   Thumpers (
-   -   How to service (some) LC4 forks (

meat popsicle 05-07-2008 11:31 PM

How to service (some) LC4 forks

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. :deal

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.


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. :bluduh

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: 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?

meat popsicle 05-07-2008 11:36 PM


Is your bike dirty? Are your forks caked with mud? You should always clean your bike up first so crap doesn’t get inside. Might as well not service it if you are just going to get dirt and crap in the fresh oil during the job… so get scrubbin’!

Get the forks off the bike

Use LC4 Laramie’s Steering head bearing, a how-to-guide… to get your forks dismounted BUT use the following changes:

1) Loosen the upper triple clamp pinch bolts, then loosen the fork caps from the outer tube, before loosening the lower triple clamp pinch bolts. This will allow you to use the lower triple clamp as a vice to hold the fork legs while you loosen - but not disconnect – the fork caps.

2) You may need to use something to pry open the triple clamps in order to slide the fork legs out. With my triple clamp pinch bolts completely removed I couldn’t budge the fork legs without wedging the clamps open a bit.

3) I removed the handlebars so I could use a socket on the fork caps. If you are dismounting your forks for service, you probably should be checking your steering head bearings, so you might as well since its part of Laramie's how-to.

Well, there they are… I wished mine were still mounted too, but ya might as well continue.

Open them up, remove the springs, and drain the oil

Open one fork leg and let the outer fork tube slide down; don’t worry fork oil won’t spill as long as its upright. Then fit your special narrow-width spanner onto the hydraulic stop, as pictured below, by pulling the spring down and holding the fork cap up.

You can now get the fork cap off the cartridge assembly. The wrench is now holding the spring down, so pull down on the spring a bit to remove the spanner and then the spring can be removed. You should notice a thin hollow rod sticking out of the inner assembly. If not, and it is sitting flush or inside the piston rod, then pay attention to the rebound needle business below. Either way pull it out; pre-2003 48mm USD forks should have a o-ring on that rod.

Now you can turn the rest of the fork upside down, gently, and pour out the oil. I said gently because if your rebound needles are not stuck and you are rough with the fork while it’s upside down they may fall out with their springs. So take it easy at this point when turning the fork leg upside down. Pumping the piston rod will help release the oil in the cartridge, and I found that leaving them upside down in my drain pan overnight helped too. I wonder if pumping the piston also helps stir up any grit that has settled out so you can pour it out with the old oil… that would be good.

Once you have drained the oil you can either continue with the disassembly or begin reassembling. You should more fully disassemble your forks if:

1) your fork oil looked bad enough to warrant some cleaning,
2) your rebound needles are frozen,
3) or you were going to replace the fork seals and/or revalve the stacks.

If the fork oil looked good, the rebound needle was springing, and no revalve and/or fork seal replacement was going to happen then you could simply pour in new fork oil, set your oil height, put in your old springs (or your new ones), and close ‘em up. (Remember new springs will require you to set the preload, which is not covered in this guide - see your fork manual.) If not, it probably would be a good idea to disassemble them and do some cleaning. If you are good to go, scan below for where to pick up with the assembly.

Now what about this rebound needle business?

Based on what the suspension tuners both said, the rebound needle is the most vulnerable part of these forks. There is no fork oil inside the inner assembly, unless you poured it in the wrong place… then you might notice oil weeping out of your rebound clicker :lol3 Anyways, the rebound assembly is not bathed in oil so the bore (made out of plain steel) can and will rust as moisture makes its way inside your forks. This will render it non-adjusting and eventually might interfere with the fork’s rebound. If for no other reason, this is why you must service your forks annually!

You can check to see if yours have rusted by pressing on the rebound adjustment rod before removing it from the inner assembly. The rod should extend a bit (less than ¼”) out of the inner assembly when properly seated on the rebound needle down yonder, and if you push on it you should feel the rebound needle’s spring. There's my lil' rod sticking out in the picture above! If not then the needle is likely frozen in the bore and will need further attention.

NOTE: the following rebound needle information in this paragraph is out of the disassembly order; I put it here to help you understand how much further you would need to disassemble in order to service the rebound needle. A trick I was told is to use a small Allen wrench to try and push the rebound needle from the bottom of the rebound assembly. Again, you can’t see it until you disassemble the cartridge, but there is a small hole on the bottom of the piston that goes straight through to the rebound needle. You can see the hole in the bottom of the rebound piston pictured below. The needle is made of soft metal so don’t push too hard! Just give it a moderate push and see if this frees up the needle so that the rebound adjustment rod sits above the piston rod and you feel the spring’s action.

If not then you will need to disassemble the rebound assembly from the piston rod, which requires a soft-jawed vice or some other way to hold the piston rod without damaging its finish while you remove the rebound assembly “complete”. The shop manual says to secure the piston rod by grabbing it along the length that will be covered up by the hydraulic stop, probably to minimize any risk to its finish. Removing the rebound assembly from the piston rod will expose the rebound needle and bore where you might be able to clean them up, depending on how neglected they were...

I watched my fork tuner open up the assembly, then make a drift out of a stout piece of soft wire (aluminum) that he rounded on a grinder, and then punch out the rebound needle through the same hole in the bottom of the rebound assembly used for the trick noted above. The needle is brass (soft) so if you have to hit it too hard you probably will damage it. He then cleaned everything up to restore the bore and needle, but again if you can’t restore the bore and needle you will have to replace them. Finally, he found one of the springs was rusted away to oblivion and the other was permanently squished from being stuck in one position. He salvaged one spring from another person’s assembly that was completely replaced and said they would probably do OK, but recommended replacing them. BOTTOM LINE: if you keep up with servicing your forks you can limit the amount of water that remains inside the fork, which will help you steer clear of this mess.

Remove cartridge and base valve from the fork tubes and disassemble it

OK (breathe), I’ll continue with the teardown and those not needing more can scan below in Post #3 for where to jump back onboard. Now you need to remove the inner assembly from the fork tubes. To do this, pry off the rubber plug covering the compression adjustment clicker on the bottom of the fork leg. You can then use a socket to remove the compression assembly (aka base valve) from the cartridge. Once you separate them you will be able to remove the cartridge and then tap the compression assembly out of the fork tubes. There is one useful tip in the shop manual on this: extend the piston rod and hold it to one side – gently bend it to one side and hold it there – which will keep the cartridge from spinning while you unscrew the base valve.

In order to reach your rebound adjustment needles and rebound valve stacks you will need to disassemble your cartridges further. But do not follow the steps in the service manual! It will guide you to remove the screw sleeve from the tube, which is a royal pain due to the number of threads and/or amount of Loctite on them. Both tuners recommended a workaround: remove the hydraulic stop/spring guide, which will allow you to drop the piston and rebound assembly out the bottom, leaving the screw sleeve and tube of the cartridge assembled. Be ready for the piston ring to fall off. And be nice to it; that is what creates the seal within the cartridge to direct oil through the rebound and compression assemblies.

That does it for the amount of disassembly I performed. This exposes the valve stacks for both rebound and compression. If you are game, here are two local threads that may help you revalve your own forks: Zerodog’s fork mods and one more with valve info. If not, but you would like to improve your forks get a tuner that knows LC4s. I know of one in San Francisco and another in Salt Lake City and both seem to know their stuff and will take care of you. As one tuner told me, the LC4a’s forks are setup very oddly by the factory; as I recall he said something to the effect of: soft springs with harsh valves is a bad combination.

If you are replacing your fork seals I can’t help you with any tips on further disassembly/reassembly for that; perhaps someone here can fill in this bit of information. :ear Here is one thread on cleaning your fork seals without disassembling: cleaning fork seals

EDIT: Zerodog has graciously added a summary of his experiences with various fork seal brands that are available for (some) LC4 forks HERE or on page 3.

meat popsicle 05-07-2008 11:41 PM


Reassemble the cartridge and connect it to the base valve in the fork leg

My tuner has freed my rebound needles and reattached them to the piston rod. Now I have to reassemble the cartridge by carefully inserting the assembled piston rod (w/ ring) into the tube. If you followed the manual you would then have to apply some blue Loctite to the screw sleeve threads and tighten it to the tube. (Odd how many fittings do not list torque values in here. :dunno) If you followed the tuners’ advice simply slide the assembled piston rod into the tube, up through the screw sleeve (don’t forget the piston ring), and thread the hydraulic stop on “hand tight”.

Remember the cartridge threads onto the compression assembly and that secures them to the axle clamps at the base of the fork tubes. Wipe a bit of fork oil on the compression assembly’s o-ring and you are ready to put them together. Don’t forget the manual’s tip to extend the piston rod and bend it to one side in order to keep the cartridge from rotating while you thread it onto the compression assembly. I believe that is a 25Nm torque value.

Pour in oil/set oil height, install springs, and fork caps (practice first!)

This is where folks who skipped out on “further disassembly” above join back in with the game. :wave First I’d recommend you practice keeping the piston rod up while installing the spring before you pour in the oil. See the next paragraph for details. This will save you some hassle, but only if you remember to remove the spring before pouring in the oil… remember the oil height is set without the springs installed!

OK, ready to pour in oil? You will need some way of standing the fork up while you fill it partially with oil, then gradually pump the piston up and down filling the cartridge with oil to release any air bubbles, and then measure the oil height and finish filling it. I used some space between two palettes and a storage bin to hold my fork tube upright:

I poured in one bottle of Redline’s suspension fluid to fill the cartridge and then used part of a second bottle to set the oil height. I used a short metric ruler (15cm) and a camper’s headlamp to measure the oil height. HERE is one thread showing the owner’s manual’s guidance to setting the oil height.

Figuring out how to install the springs while keeping the piston rod up, or how to raise it back up, can be hard the first few times. I know, I know, this is a common problem; no need to dwell... :nono Either extend the piston rod all the way up and then slide the spring over it, or use string to pull the piston rod up thru the spring. You can quickly, but in a controlled movement, slide the spring over the guide and then catch the piston rod before it falls down. If it falls down too far to catch through the top of the spring one tuner said catch it where you can by bending the spring slightly and then use your special spanner on the hydraulic stop’s nut (the one on the spring guide that you use to remove the fork cap) to “screw” the piston rod back up by rotating the spanner around the spring.

OK, push the spring down and get your spanner on that nut so you can thread on the fork cap, which should also be torqued to 25Nm I believe. Now you can raise the fork leg tube and thread it onto the fork cap “hand tight”. That is all it needs because the upper triple clamps over this area and holds the two together. And that should do it! If you want to read my notes on further reassembly of the front end take a look HERE.

Also review Neduro’s Spring Bike Maintenance and Setup Guide for specific tips on the LC4’s WP forks setup (i.e. dealing with stiction).

Hope that helps. :beer

Other tidbits:

Here are a few HOWDIDs with some good (and a lil’ bad… ) info: Gaspipe’s Emig Damper and Triple Clamps and Motolard’s LC4 steering head and fork service notes

In case you are particular about your Loctites here are KTM WP Loctite codes demystified:
T131=loctite 243
T132=loctite 2701
T163=loctite 648

A few random fork threads:

And a few Sag threads (some already in LC4 Index):

Zerodog 05-08-2008 01:27 PM

Looks good Meat! Did you ride it yet?

1stworks 05-08-2008 01:46 PM

Thanks for that post!!!:D


meat popsicle 05-08-2008 02:13 PM


Originally Posted by Zerodog
Looks good Meat! Did you ride it yet?

I had a little repair to take care of first (done), and now I am completing setup and such. Headlight wiring upgrade will wait until I have her out and about some - should be soon! :ricky

I am being delayed by other work - building a house, getting the veg. garden in, and some professional stuff has been keeping me busy.

meat popsicle 05-08-2008 10:14 PM


Originally Posted by firstworks
Thanks for that post!!!:D


I'll need someone to try it out and let me know how it works. Then I'll need quite a few to say OK before it gets included in the index's how-to section. Zerodog's vote means alot, but I still need some folks trying it who are not professional LC4 suspension tuners. :lol3

Right now it's not fairing so well... well, it is kinda wordy so folks might easily glaze over unless they really need it. But there was a helluva lot more to say than that! The above text is somewhere past draft 10. It was hard cutting out so much of the "why".

creeper 05-09-2008 03:40 PM


Originally Posted by meat popsicle
It was hard cutting out so much of the "why".

It's a bitch ain't it. :poser

Good job Meatski... don't be discouraged about the post count, refurbishing forks isn't one of those things that your average rider will do for shits and grins... especially at the beginning of summer.

Considering what LC4 DIYs are already done, there wasn't a whole lot left for you to sink your teeth into... but to your credit, you found something that will be practical and beneficial for most everybody, once they realize that it's not rocket surgery... and that fresh forks are good forks.

Don't let the bastadges get ye down brudder...


bmwktmbill 05-09-2008 11:29 PM

What a work of love for WP suspension. Don't apologize for anything, your work is just great and none of this is simple stuff.

The WP fork is really an excellent component and easily adjustable but as you pointed out, much misunderstood. I can recommend Z-dogs stacks. Your work on the rebound needle is priceless. Get the right spring for your weight and a great suspension is born.

When I traveled in Asia I saw so many broken or leaking suspensions it was ridiculous. Beemers, Kaws, Suzuki, Yams, you name it, it failed.
I never saw a WP fork with a problem.
Thanks for your efforts.

meat popsicle 05-13-2008 09:29 AM


Originally Posted by bmwktmbill

... Your work on the rebound needle is priceless.

... Thanks for your efforts.

Thanks Bill,

Just wanted to point out that most of the knowledge above is thanks to the two WP suspension tuners I linked to above. A little bit is gleaned from other threads here, but the only thing I did was heard it into one thread.

meat popsicle 06-23-2008 10:03 AM

Herding more LC4 fork maintenance info into this thread:

WP 50mm Question??

meat popsicle 07-18-2008 03:12 PM

The KTM Talk thread that I linked to above just keeps getting better and better!

Read thru it; those fellas are showing everyone a bunch of detail on how to work on forks. :deal

meat popsicle 07-29-2008 08:30 AM

Zerodog has posted the way to align your front end while installing the fork tubes, while correcting me HERE.

I'll be checking mine today. Thanks again ZD :beer

meat popsicle 08-07-2008 09:51 AM

Zerodog posted a pro's method for servicing forks HERE. So there is the difference between how a pro gets it done and how a diy muddles through... :lol3

One more merge; an old thread on fork seal changes:

meat popsicle 10-24-2008 05:54 AM

I came across THIS post on an unrelated quest. Even creeper's rebound valve was fukt up.

Times are GMT -7.   It's 07:19 AM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015