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YSS 238 PD Valve in RD350LC Fork


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Got some YSS 238 cartridge emulators I want to fit to a pair of RD350LC fork legs I'm building.

According to interweb you need to " mill a bit off the OD" to achieve the required minimum of 3mm difference between the spring diameter (26mm RD350LC) and the cartridges od (23.8mm).

So unmodified only 2.2mm clearance.

This looks to me to give rebound flow path sufficient clearance.

Looking at the valves ( arrived today) there is not a lot of metal to remove 0.8mm from the diameter on the lathe, but is possible. 

The alternative MIGHT be to mill a couple of slight flats , removing 0.4mm , on the od of the valve?

Any one any thoughts ?

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I've never found a PD valve installation to have too much rebound damping.  If you've got the time to play around and get it right I would leave the valves original and install them.

Start with 10w oil with a 160mm air gap and see how they feel.  If the rebound is good, winner - winner, if not then consider changing the oil to a 5wt for less rebound or a 15 or 20 wt for more rebound.  Once you've got that sorted then adjust the preload on the PD valve spring to set the compression damping for that weight of oil.

If you really can't get the rebound away from being too much (which I really doubt to be honest) then consider removing some metal, but try and make it work before getting the angle grinder out ;)

Are you installing YSS springs too?

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I think I need some 26mm od 8N springs, not found any so far for what I consider a reasonable price (£80 ish) but was going to have a look at the original springs, measure the wire diameter and no of coils then maybe cut some coils of and play around with spacers.

If it goes like any of my usual projects, I will waste a lot of time and effort playing around before sourcing and buying what I should have bought in the first place.


Some trite comment like “Its about the journey” might fit in here.


Anyway many thanks for the reply.

As I had my shoulder rebuilt two weeks ago I’m pretty useless at the moment, but got Junior to stick around long enough to put a YSS rear shock in, with a standard front end I rebuilt previously front and rear move pretty much together when you bounce the bike, so I’m guessing the preload on the standard weedy progressive springs is about right. Being a lazy git I haven’t measured the static and rider sag yet, but promise to do so as soon as I have two functional arms.


Next stop the loft to get a set of crusty LC forks, strip them and get the lowers vapour blasted.




Edited by DougW
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