How To: Fit YSS PD Valves into IT forks

[mboddy]

This topic shows how I fitted YSS PD Valves to the forks on my 1979 IT175F.

I did a similar topic on the TDR250 forum when I fitted Race Tech Gold Valve Emulators to the TDR250.
http://tdr250.co.uk/forum/viewtopic.php?f=17&t=233

I use the Gold Valves in all my Historic Road Race bikes.
http://www.shocktreatment.com.au/emulator.html

Race Tech have new web pages for Vintage Dirt Bikes.
http://old.racetech.com/evalving/menu/searchdirt.asp

The YSS PD Valves are similar to the Gold Valves but are about two thirds the cost.
http://www.yss-australia.com/products_yss_pdforkvalve.php

Graeme from OzVMX evaluated YSS suspension including the PD Valves.
http://www.ozvmx.com/market/yss.htm

This kit is 265 for 36mm IT forks.



Undo axle and remove front wheel. Undo brake cable clamp and speedo cable clamp.

   




Remove rubber covers and loosen fork caps. Measure how much forks are pushed through. Loosen headlight bracket screw.

   

   


Loosen fork clamp bolts and remove forks.

   


Remove fork gaiters and caps and pull out springs.

       


To take the fork apart you need a 8mm allen socket for the lower bolt and a 19mm allen socket with long extension for the damper rod.








Check that the PD Valve sits correctly on the damper rod.




Six 8mm holes must be drilled in each damper rod. They must be at least 10mm between centres.
The original four holes are closer than 10mm and so I tilted the damper rod when I drilled out the original holes.










Holes are chamfered using a file.




A modified and an unmodified damper rod.




I cut the spring spacers down by 14.3mm which I measured was the extra length added by the PD Valve.
I didn't have a tube cutter and so I scribed where I wanted to cut and then used a hacksaw and a file.  






The PD Valve spring preload should initially be set to two turns. Undo the lock nut and loosen the allen bolt.
Hold the Valve loosely in your fingers and rotate the bolt until the valve rotates. Then tighten two turns.
I put the 4mm allen T-Bar in the vice and held the valve while tightening so that I didn't give it any extra preload.    

   




Fit the forks.

You can adjust the compression damping action with more or less valve spring preload. Just fish it out of the fork using a magnet on a stick.

Put in the required amount of 10wt fork oil. Move the legs up and down to get any trapped air out.
Drop the valve into the fork, then spring, spring seat, and spacer. Fit the caps and tighten them.

   




Fit the wheel and tighten all the screws.

   




Take it for a ride.

 

[mboddy]

Took it to the MX track today.
Even thought it was really muddy and bikes were dropping like flys I didn't drop it!
So I reckon the PD Valves were well worth the money. 

[Griffo]

Did you end up changing the valve from the initial setting, or are they good enough with the base 2 turns of preload?

[mboddy]

They feel pretty good both when I had a small ride a couple of weeks ago and today in the mud.
I'll keep them as is for RDR2 and see if they need any adjustments then.
I reckon that I'll more likely be fine tuning the rear to match the front now though.

[ITsa490]

That sounds like a sweet conversion mark, do you think it can be done to a 490...more so would it be a similar task or more complex?

[Griffo]

I was eyeing off a set of these about a year ago....
My forks are due for a freshen up, so a set of these sound like the go!
So, kit 290 for my forks you say....

[mboddy]

do you think it can be done to a 490...more so would it be a similar task or more complex?

You could do it to a 490 and it would be pretty much the same as what I had to do on the 175.

Either YSS PD Valves or Race Tech Gold Valve Emulators could be used and the procedure would be the same.

Only the 76-78 C, D and E models are trickier because they need an extra adapter.
For 77-78 D and E model 250 and 400 I think you can fit IT175F damper rods and only lose 5mm travel.
It was easy to find bent or rusty IT175F forks cheap to donate the damper rods.
I'll try it with my IT250D and add the pics to this thread.    

Hold back on ordering yours until you can measure your forks Griffo.
The YSS and Race Tech recommendations need to be confirmed because they have not always been 100% accurate.
It may just be the earlier models that they are out for. I know with my Yamaha road bikes that the earlier ones have thicker tubes.

It is best to measure the diameter of the damper rod piston but that involves stripping the forks.
It should be close to the diameter of your springs. Can you measure that for us Griffo and itsa490 please.
Graeme and Dave are going to measure theirs (IT175G and IT200L).
How about you Jock? Can you measure the IT125 spring diameter?

[Griffo]

I try to rip my bad girls apart on the weekend!

[ITsa490]

That sounds dangerous griff, will you post us the pics...

[Griffo]

f__k I'm slack...! 

[Hedgy]

We all know that

[Griffo]

So which part of the damper rod do I measure? I now finally have a set (Juzzy's) of 465 38mm forks apart in the shed!

[mboddy]

The diameter of the damper rod piston. (Not the diameter of the damper rod piston ring if different).

[Cookie]

Griffo' let me know what the piton diameter is, I could probably do with getting a set for my 465.

Cheers

Cookie

[Griffo]

Ok, Damper rod piston measures up at 30.6mm.
So 290's it is!... When I'm not so poor