Search Our Site
Your Suspension Expert
Walter Preisig
Your Suspension Shop is located in Adelaide, South Australia, and was established by Walter Preisig to service the Australian bike market with a new generation of gas shock absorbers that are continuously under development by Walter in partnership with Hyperpro and YSS. Walter has been developing racing suspension for over 25 years and has a wealth of experience in suspension technics, motorcycle maintenance and customer service.
Go to Harley Suspension
Philosophy
“ It's unwise paying too much, but worse paying too little. By paying too much, you lose a little money. By paying too little, you could lose everything, because what you've bought would be incapable of doing what it was bought for. The law of business balance prohibits paying a little and getting a lot. If you deal with the lowest bidder, it's wise to add a bit for the risk you run and if you do that, you can pay for something better. "
That said and with this in mind, Your Suspension Shop is servicing the motorcycle community in Australia and overseas as well as furthering the research, manufacture and development of top quality world class shock absorbers for racing purposes and casual driving without breaking your bank.
Now accepting Cards
“ Installed YSS fork valves and progressive springs last week and tried them out on a ride yesterday (Saturday). Unbelievable difference. Gone is the bottoming out on sharp bumps and they instill confidence on turn in as dive is reduced. Cost was $630.00 supplied and installed. "
Glenn Wainrib, Melbourne AUS
“ Just thought I'd let you know Walter the new YSS's on the 490 were great on those rough NSW cow tracks, could even actually walk after Lakes meeting. "
Legend, Newcastle NSW
“ Woooo Hooo. :-) :-) They arrived today. They fitted perfectly with NO mucking around, look fantastic. Overall finish is very pleasing and nicely put together. Feel great when bounching on the bike. Damn, I got this thing rego'd. :-) "
Quicksilver AUS
YSS PD Fork Valves and Technical Fork Valve Assembly Guide
Go to PD Valve Technical Explanation - How does it work ? ♦ Go to Fork Valves - Why and How ?
OD 42.5 mm YSS PD Fork Valves
YSS PD Fork Valves give that progressive and controlled feeling of a cartridge fork. The PD Fork Valve has a radial computer designed valve housing made of 6061 T6 aluminium for light weight and is 65 Rockwell hardened for long life and appearance.
YSS PD Fork Valves are damping adjustable and tuneable to any application and they are Easy to install as well as extremely cost effective. YSS PD Fork Valves can be used for On- and Off-Road, Racing and Touring.
They are fully tested by YSS and proven to perform as you would expect from a superior YSS product. Our PD Fork Valves suit all brands of motorcycles with conventional forks, such as BMW, Harley Davision, Honda, Kawasaki, Suzuki, Triumph and Yamaha. PD Fork Valves are available in the following OD sizes: 17.5 mm, 31.0 mm, 23.8 mm, 33.5 mm, 26.5 mm, 36.0 mm, 29.0 mm, 42.5 mm
Call the Suspension Shop on +61 (08) 8284 8033 or visit us at LOT 257 Heaslip Road in McDonald Park 5121, South Australia - Our Suspension Shop has a huge stock of Fork Valves in the Warehouse for immediate fitting or dispatch.
We recommend you select the correct fork spring for your motorbike and that you check the proper fit before you install your PD Fork Valves. Call Your Suspension Shop on +61 (08) 8284 8033 for any questions you have regarding PD Fork Valves and selecting recommended Fork Springs.
How to choose the right size of PD Valves
Measuring the OD of a Damperrod.
Option 1)
Measure the OD of your Damperrod as shown in the picture and choose the next PD Valve Size down.
Example:
Rod OD 28.91 => PD OD 26.5 mm
Available PD Valve Sizes:
PD Valve OD 17.5 mm
PD Valve OD 23.8 mm
PD Valve OD 26.5 mm
PD Valve OD 29.0 mm
PD Valve OD 31.0 mm
PD Valve OD 33.5 mm
PD Valve OD 36.0 mm
PD Valve OD 42.5 mm
Measuring the OD of a Forkspring.
Option 2)
Measure the OD of your existing Forkspring as shown and choose the next PD Valve Size down.
Example:
Spring OD 43.47 => PD OD 42.5 mm
Available PD Valve Sizes:
PD Valve OD 17.5 mm
PD Valve OD 23.8 mm
PD Valve OD 26.5 mm
PD Valve OD 29.0 mm
PD Valve OD 31.0 mm
PD Valve OD 33.5 mm
PD Valve OD 36.0 mm
PD Valve OD 42.5 mm
Tool Requirements for PD Fork Valve Assembly
| Required Tools | Diagram for PD Fork Valve Assembly |
|---|---|
|
|
YSS PD Fork Valves
PD Fork Valve Assembly DiagramStep-by-Step Guide for PD Fork Valve Assembly
| NOTE: All these steps should be done by a qualified suspension mechanic. Or Suspension Shop is NOT responsible for any damage to shock absorbers, vehicles or injury to persons, if the instructions are not exactly followed. The warranty will also be void. | |
|---|---|
| Note | Assembly Steps for PD Fork Valve Installation |
PD Fork Valves are available in the following sizes for Motorcycles with Conventional Forks:
|
|
Tuning Options for PD Fork Valves
| Tuning | Standard | Optional | Advantage |
|---|---|---|---|
| (1.) Oil Viscosity | 10W | 15W, 20W, 30W | More or less rebound depends on viscosity to make stability |
| (2.) Valve Spring Preload | (3.) Two (2) Turns | 0 to 7 | Overall firmness, controlling the speed of front end dives under braking |
| Valve Spring Rate | 7 N for 175, 235, 265, 290 12 N for 310, 335, 360, 425 |
12 N 7 N |
Overall firmness and smooth ride on square shaped bumps |
|
|||
Fork Valves - Why and How ? - (Words by Ken Smith)
Practically all the dirt bikes from the '70s and early '80s that we ride still utilise holes in the damper rods to control the compression and rebound damping action. Cheap to make initially and they sort of did the trick, even though they were no further advanced than forks from decades earlier.
Why change to fork valves?
For those of us who did want to get all 'techno' with our forks in the '70s, we had basically two options to alter fork damping - change oil weight or change the size of the holes in the forks. Just to refresh your memory, oil gets forced up through those holes in the bottom of your damper rod, to control the compression damping. So, changing the fork oil weight and/or the size of the holes will have an effect.
However, the basic problem with that design is that it is not producing a progressive damping curve. That is because TOO MUCH oil goes through the holes to produce adequate low speed damping and TOO LITTLE oil is able to pass through the holes to provide enough high speed damping. The forks dive too much over small bumps or because of braking AND suffer hydraulic lock when they get a really big hit - you got it, neither actuality is catered for sufficiently and if you try to fix one end of the spectrum (say, making the holes bigger to improve high speed damping) then you compound the problem at the other end (i.e. make low speed damping even worse).
So along comes the cartridge fork, except, it's a wee bit difficult to just rip out the innards of a cartridge fork assembly and shove it in your tiny 35mm forks. Hence, the introduction of fork valves such as the PD units, which we've used for our installation example that follows. What do these fork valves achieve that's similar in operation to cartridge forks?
While a set of fork valves will never work as well as a proper cartridge system, they will provide a progressive damping response, utilizing a single, spring-loaded shim to control the compression damping. Low oil velocity past the shim opens it a little and provides more damping - high oil velocity opens the shim more and provides less damping. Fork valves will not have any effect on the rebound damping, that will still be controlled by the existing holes towards the top of your damper rod, and, will still be 'tunable' by way of differing oil weights. Different oil weights will still have an effect on compression damping but not as much as it will affect rebound damping. Compression damping, once fork valves are installed, will be primarily controlled by the spring preload you set on the valve.
Before we get on to the installation process, we'll just explain the other basics. The fork valve sits on top of the damper rod (between the top of the damper rod and the spring) and is "fed" oil that is forced up the centre of the damper rod. Therefore, extra holes must be drilled in the vicinity of the existing compression damping holes at the bottom of the damper rod. In essence, you don't want the lower holes performing ANY restrictive function, and consequently, the area of the lower holes must be at least equal to or greater than the area of the hole down the centre of the damping rod. The valve on top of the damper rod will now control compression damping exclusively. Finally, because you have added what is effectively a 'spacer' between the top of the damper rod and spring, you will need to shorten any existing spacers in the forks by a corresponding amount (as in the height of the fork valve you're installing). Assuming of course that you're happy with your existing spring rate, static sag and so on - make those measurements and decisions before you start... ...speaking of which, let's get this show on the road.
Installation
1. a and b. Take the forks out of the bike and disassemble forks on the bench. An impact/rattle gun is a handy item to get those bottom fork bolts undone, or, in the situation where they still won't come undone, a combination of impact wrench and a special tool that holds the damper rod in place.
2. Once apart, you can do a simple check for any bends in the fork tubes. Just hold them against one another, roll them both around and check for any gaps between the two. Simple.
3. You will have already chosen what size fork valves you require, based on the internal diameter of your fork tubes (measure in a smooth section, not a threaded portion, where the fork top nuts thread in for example). However, you need to check that the valve fits properly on the top of the damper rod. There is a small step in the underside of the valve and this must fit neatly in the recess in the top of the damper rod to 'locate' it properly. If it doesn't sit properly, or, you have a valve size that may not be entirely correct, you will end up with a valve that sits skew, like in the photo. This will render the valve ineffective, as oil will escape around the outside of the valve. All the oil that is forced up the inside of the damper rod must flow THROUGH the valve. This photo shows a valve that is not sitting correctly.
4. Your valve should sit 'square' on top of the damper rod as per the photo. In some cases, you may need to machine a ring, which fits between the top of the damper rod and the valve, for it sit properly. If this is the case, then it may be time to take the whole box and dice to a suspension expert! You will also need to check that the inner diameter of your fork spring is 3-4mm larger than the diameter of the raised 'plate', or step, on the top side of the fork valve. And yes, all these points are outlined in the instructions.
5. a and b. Time for some drilling. The instructions provide you with some guidance, for example, if your damper rod is 17.5mm diameter (ours was 17mm) then you'll need four holes of 6mm diameter. Our damper rod already had four holes of 5mm so we enlarged those to 6mm and added two additional holes for good measure. Do not go overboard though as you will weaken the rod. Standard rod on left, modified rod on right. Don't forget to chamfer and deburr holes.
Re-assemble forks and enjoy the ride.
YSS PD Fork Valves suit All Motorcycles with Conventional Forks
PD Fork Valves - Easy Installation - Order Online Here
Fork Basics: Why Some Forks Work And Some Not
As you know, the forks contain a certain amount of oil who's purpose is to control the rate, or speed the forks compress and rebound, ie: go up and return to their normal level. As the forks are compressed the oil is forced through one set of holes - orifices to be precise. The size and number of holes coupled with the viscosity of the oil determine how quickly the oil will flow from one chamber (A) to another (B). When the forks extend themselves, the oil has to return from chamber B to chamber A via another set of holes. This gives us our compression and rebound damping.
The main fault with standard forks is that the only means of adjusting the compression damping is by changing the viscosity of the oil. This will also affect the rebound damping since the same oil must return to its original chamber. The upshot of all this is: change one and affect the other. It's not possible to simply change the compression damping independently of the rebound damping and vice versa. Unless of course you want to get involved in drilling the existing holes.
Another factor also needs to be taken into account at this point and that is the need for low and high speed compression damping, and NO, we are not talking about high speed as in kph. or mph., but the speed at which the forks compress. Small bumps equate to low speed compression damping whereas pot holes, ridges and oh shit! handfulls of brake mean high speed compression damping of the front forks. The standard fork set up cannot differentiate between low and high speed compression as there is only one set control holes. That's why on one hand your forks may feel mushy on smooth roads and in normal braking situations and yet feel quite harsh when encountering potholes and ridges in the road.
What is obviously needed here is a damping system that can differentiate between low and high speed damping. This is what " PD Valves " do. Not only do they differentiate between low and high speed bumps but you can adjust them to give you the type of ride that you want, or, to suit the type of application you require, ie, soft for cruising or firm for track days and fun motorcycling. Did we forget to mention that these adjustments do not affect the rebound damping? Sounds too good to be true doesn't it? But they work and work bloody well. Just how they work we'll cover later in this article. Lets first see how the standard forks work.
When A Bump Is Encountered
When a bump is encountered the fork slider rises up the fork tube; at this moment the following happens:
1. The ball check valve opens,
2. Rebound check valve opens,
3. The oil in chamber A flows a) into chamber B and b) through the compression damping holes at the bottom of the damper rod and exits through the top of the damper rod through two more compression damping holes into chamber C.
As you can see, the flow of oil is controlled only by the size of the holes at the top and bottom of the damper rod.
As the forks extend themselves the oil above the damper rod in chamber C flows back to chamber A and the oil in chamber B flows back to chamber A via the rebound damping hole and also in a controlled way past the clearance between the rebound check valve and the damper rod.
When The Forks Extend
1. The ball check valve closes,
2. the rebound check valve closes stopping the free flow of oil through the valve, and forcing it through the small rebound hole in the damper rod.
As you can see there are 2 different circuits. One for compression damping, and one for rebound.
It could be simplified by saying that chamber A provides the compression damping and chamber B the rebound damping.
What Does The PD Forkvalve Do?
To fit the PD Forkvalve the ball check valve at the top of the damper rod is removed and six 8mm holes are drilled at the bottom of the damper rod in place of the compression damping holes.
By doing these mods we completely nullify the standard compression damping system.
The six 8mm holes flow sufficient oil to prevent any compression damping taking place, leaving the oil free to travel to the PD Forkvalve where the real work is done.
You'll notice that nothing has been done to affect the rebound damping. Chamber B remains the same, so that our rebound damping stays constant.
With the PD Forkvalves fitted the viscosity of the oil affects only the rebound damping so adjustment of the rebound damping is made by changing the oil. ie: thicker oil slower rebound, thinner oil quicker rebound.
The size of the holes in the damper rod and the port size of the PD Forkvalve for the sake of this discussion are not affected by the grade of oil.
Low Speed Compression Damping
Here we see that the oil is free to leave chamber A, flow through the damper rod and exit the PD Forkvalve through a small hole in the emulator plate.
This small hole gives us our low speed compression damping.
The theory being low speed movement only requires a small hole to control the small amount of oil passing through.
High Speed Compression Damping
We've hit a pot hole and the forks are sliding up the stanchions fast.
The speed and pressure of the oil has lifted the PD Forkvalve plate off of it's seat opening up larger ports for the oil to flow through quickly.
The faster the forks move the more the PD Forkvalve plate lifts off its seat thus flowing a greater amount of oil.
You'll notice that the spring on top of the PD Forkvalve plate can be adjusted to increase or decrease the pressure on the plate. This is how we adjust the PD Forkvalve.
Rebound Compression Damping
With the forks now extending back to their normal position the check plate in the PD Forkvalve has fully opened allowing the oil in chamber C to return unrestricted to chamber A.
The rebound compression damping is controlled by the small rebound damping hole, the seepage of oil past the rebound check valve and the weight of the oil.
We now have fully adjustable front forks.
The adjustment of the PD Forkvalve is quite infinite. One turn of the adjusting screw will give a plush ride. Three turns is quite firm. The choice is yours.
As mentioned before, the rebound is adjusted by changing the viscosity of the oil in the forks.
The PD Forkvalves can be quickly removed from the forks by undoing the fork cap, pulling out the spring and then hooking out the PD Forkvalve with a bent piece of wire.
Benefits
They will reduce the front-end dive especially when braking.
They will give feedback - and so give you confidence to go faster mid corner.
They will stop weird handling wobbles and bobbles if adjusted properly. .
PD Fork Valves for your Motorcycle
Your Suspension Shop has a vast range of products at hand - ready made and also customised for any motorcycle. Feel free to call YOUR SUSPENSION SHOP to discuss a solution for your technical needs.
