WP Fork Oil Level

[MattR]

I changed my fork oil tonight in my WP's and according to the WP manual it mentioned to set it 25 mm below the 4 holes in the inner tube. Well, this is approximately 100 mm down from the top when the fork is fully collapsed. After reading some older posts on Talking Smack, it sounds like the common oil level is around 130 to 150 mm from the top. At this point, my forks are reassembled but not on my bike yet. Now is the time to reset the oil level if needed.

What oil level do you recommend?

What is the damping effect of 100 mm vs. 140 mm? I guessing increased bottoming resistance due to smaller volume of air... Will it be too harsh?

 

[GMP]

Matt,

That sounds too high to me, and I suspect things will be harsh.

The correct method is to first fill to the top of the inner tube (over the 4 holes) until all the air is expelled from between the tubes. Then bleed the cartridge and adjust the level. I run 110 - 115 mm with 90cc subtanks, and I never bottom even in big whoops. I would go back into the forks and fill over the holes, then drop the level to 140 - 150 mm.

 

[Dave]

The WP manual has you reduce the oil level below the holes and then raise the rod and outer leg. This "dumps" the oil that was between the legs. So the 100mm air chamber WP asks for using their procedure equals about 140mm without "dumping" the legs.

 

[MattR]

Well, I opened my forks back up tonight and readjusted the oil level per Glenn's recommendation. I set it at 140 mm from the top. I hope to get out this weekend and try it out. However, it has been raining a lot here and my usual riding places turn to "swamps" when it rains.

By the way, I don't know what method you used for setting the oil height but my method works great!

Here is what I did:

• Took a small diameter clear tube that was a couple feet in length.
• Marked off 140 mm from one end of the tube.
• Put a zip-tie around the clear tube at the 140 mm mark and cut the zip-tie leaving a couple inch tail.
• Inserted the clear tube into the oil (between inner tube and cartridge) until the zip-tie sat on top of the fork tube (with it fully collapsed).
• Put another zip-tie and lightly tied the hanging clear tube to the side of the outer tube to keep everything stable.
• Took a large syringe and attached it to the opposite end of the clear tube and drew a vacuum sucking up oil into the clear tube.
• Emptied my syringe a couple times and continued until no more oil would get sucked up into the tube.
• Basically, it was like a big straw that was inserted 140 mm... thereby only allowing you to suck up fluid until the bottom of the straw got exposed.

 

[GMP]

When you do it this way, how far do you extend the fork? If you extend it too far without the cartridge, you can move the lower holes past the seal. I guess its OK as long as your consistant. Most tuners seem to referance oil levels in the 130 - 150 range, so I assume they use the other method. I suspect the WP method makes adjusting the oil level eaiser without a complete change, as you do not need to add oil past the holes.

 

[MattR]

Hey Glenn,

Not sure if your comments were for Dave or me.

Here's what I did:
I had the fork fully collapsed with the spring and thin adjusting tube removed.
I added oil until past the 4 holes and waited for the bubbles to stop.
Bleed the cartridge by stoking it up and down until I got consisent resistance.
With everything fully collapsed, I used my syringe device to remove oil to get the level at 140 mm from the top of tube (oil is now below the holes).

Hope I didn't booger it up again!

 

[GMP]

Matt,

I was replying to Dave, probably while you were replying as I didn't see your post.

Anyway, you did it as I do and it should be fine. I have a fork oil level tool thats like a turkey baster with an aluminum tube, and a small collar that you can clamp at different heights with a setscrew. You just set the collar for the desired oil level, stick it in the fork until the collar rests on the edge of the tube, and draw oil out until you get air.

 

[clw]

Allowing the oil to spill out of the void between the 2 tubes is preferred by some because it allows a direct comparision between the after service condition and the pre-service condition. If you want to tune the oil level and don't know the previous by the book measurement (using the GMP/WP/KTM way) you measure it upon disassembly and adjust accordingly when refilling by setting the new oil height after activating the tubes. The difference is about 30mm as I recall(don't quote me on that).

For a check do the GMP method, assemble, pump the tubes, diassemble and again measure the oil level. Instead of 150 it will be in the 120's. KTM issued a service bulletin on this a few years ago.

Did that make sense?

 

[GMP]

Yes, thats what I ment about being eaiser to set/adjust the level without refilling over the holes in the inner tube. For me its no concern since I always change the oil when the forks are off for any reason.

 

[MattR]

Well, I went riding today at my usual spot (Maumee State Forest). It provided a good comparison of the "before and after" effects of the fork oil change. WOW!!! my bike felt awesome. The whoops which usually caused me to bottom out previously were no issue now. It felt like I was riding more in the middle of the stroke and the forks would eat up everything.

Changing the fork oil will be a must on my "to-do" list each year. My bike felt so different that I plan to send both my fork and shock to Les @ LT-Racing for a complete teardown and rebuild this winter.

Hey Les, what do you typically charge for fork and shock rebuilds... of course part costs are additional. I will probably have you do some tweaking too just to make sure it is setup best for my weight. Please send me a PM if you don't want to post here. Thanks!

 

[LTRace]

Hello Matt,

Here are the retail prices for a typical re-valve and setup that I charge;

Fork rework/setup including fluid and shims $149.95
Fork springs (with revalve) $85 ($14 off of retail)
Shock rework/setup including fluid and shims $139.95
Shock spring (with revalve) $90 ($15 off of retail)
Fork oil seals if needed (depending on application) typically $29 to $32 pair

As noted, this includes high quality fluid and valving shims. Most shops charge for each individual shim plus the fluid, this can add up really fast.

Thank you Matt,
Les

 

[MattR]

Thanks Les for responding. I was hoping you would see your name in my previous post. I will get in touch with you this winter for reworking the front and rear.