I have a set of 46mm inverted Yz125 or 250 front forks in my shop. I bought them a few years ago with the intent of re-valving them, but for reasons unbeknownst to me they got buried. I don't remember what I bought, so I'm enlisting the genius of the forum experts to lend me a hand in figuring this out.

They are definitely 46mm and I would like to rebuild them for my 01 yz250.

Any info would be greatly appreciated.

The same minus the springs

kan3
Thank you for the response. I figured as much for sprig rate, but I was wondering if there were any other differences. Something that would help me visually identify them, such as markings, or parts.

Everything you wanted to know about YZ forks, and then some:

Here is a quick run-down on Yamaha forks, from 2001 - 2003.  Basically, these forks are the same with the exception of the mv piston.  The 01 may have the one-piece mv piston, and the 02-03 has the two-piece mv piston.  But, I'm not 100% sure about the 01.

Here are pictures of the one-piece and two-piece mv pist.

- - - I'm having problems getting these images and video to work. . . . Sometimes they do, sometimes they don't. ? ?  I guess you need to respond and let me know if you can't view them, and we'll we'll figure out how to get them working - - - -

http://www.valvinglo...v//DSC02664.JPG

http://www.valvinglo...v//DSC04592.JPG


The outer tube diameter that fits the triple clamps for 01-03 are 53.95 mm at the top and 58.40 mm at the bottom.

The chrome tube dia from 01-03 was 46mm.  (04 has 48mm tube)

These forks have the CV valve (cartridge valve), which basically means all the oil blows out thru the seal assy (at the top of the cartridge) on the compression and rebound stroke.  You can watch this video to see the oil blowing out the top.

http://www.valvinglo...by_04yzf450.MPG

The bv piston diameter is 28mm.

If you are going to revalve these forks, pm me and I can give you some info about the CV valve.  (I say pm me because I don't want to bore everyone with 10 year old fork info).

Regards,
Kevin

Edited by kevinstillwell, 02 July 2012 - 11:20 AM.

Nothing boring here!

Could you please give more information about the CV?
I've done a few of these forks and havent got the idea behind it/the problems which are involved.
But there are some aftermarket sealheads out there, so it seems to be a problem which has to be dealed with!

What are we looking for on the video?

The video shows the oil blowing out thru the top of the cartridge.  This oil should be going thru the base valve piston.

Hard to see. The video is very short (2 seconds) and very small. At least on my PC.

Okay, so it doesnt seal properly. Why would KYB invented the CV?
Is there a way to fix this problem without replacing the sealhead?