| Contents
Design How the shocks work Optional base plate External adjuster Options Technical info |
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The new Öhlins WCJ, MCJ and STJ stock car series (shocks with main body reservoir), are all based on Öhlins successful application of the de Carbon concept that has won more than 80 World Championship titles.
The de Carbon concept; the damping oil placed under pressure by gas and separated from the gas by a floating piston, has several advantages. It prevents cavitation. Offers better cooling. Gives more consistent damping and a longer damper life.
Designed according to the different stock car regulations the new Öhlins series features a single, double acting, external adjuster, a lightweight aluminium body with a large built in reservoir, at the top of the shock, containing the floating piston and nitrogen.
The main piston is specially developed for oval track racing. Thanks to the shape of the orifices in the piston the damping force builds up rapidly. The result is excellent short stroke/high force performance.
The internal pressure is balanced to cope with temperature build up and to prevent any chance of cavitation, yet reducing the oil compressibility and the friction from the pistons and the shaft seal.
The new Öhlins stock car series is built to perform and endure! They are easy to set up and to sort out. Thanks to the design of the main body they are also easy to maintain and to rebuild.
All Öhlins shock absorbers are built with a desire to win and with precision that ends up in quality, a quality you can see and feel.
Compression damping
During a compression
stroke path 1, fig. 1, is closed, the oil can flow through the paths 2
and 3. The damping forces at a certain compression speed are determined
by the flow restrictions in these paths.
The flow restriction through path 2 is determined by how much the oil pressure
can open the compression shims which are closed shut whenever the pressure
is too low or the shock is not moving in a compression mode.
The shim stack´s resistance to opening is decided by the quantity,
thickness and diameters of the shims, and are carefully chosen to make
each shock give optimum results.
Path 3 is the main bleed valve, the larger the orifice the less oil flows
through path 2 making the main valve compression forces lower.
Rebound damping
During rebound
stroke path 2, fig. 2, is closed and oil can pass through paths 1 and 3.
Damping forces are determined by the flow restriction in paths 1 and 3.
The flow restriction through path 1 is determined by how much the oil pressure
can open the rebound shims which are shut close whenever the pressure is
too low or the shock is not moving in a rebound mode.
These shims are also carefully chosen to give the best set-up.
Path 3 is the main bleed valve, the larger the orifice the less oil flows
through path 1 making the main valve rebound forces lower. The adjuster
knob adjusts the size of the orifice.
Base
plate
Optional for
the Öhlins WCJ and MCJ shock absorbers (not for the STJ) is a base
plate, which allows the damper to be more responsive, smoother and safer.
This base plate eliminates the cavitation risk, without the need of increased
gas pressure. It consists of a fixed dividing wall with orifices and with
shims on both sides.
In the centre there is a jet that comes in different sizes.
The stiffer the compression valving on the main piston, the smaller the
hole in the base plate jet.
The oil that flows through the base plate is the volume of the shaft displacement,
which also moves the floating piston.
The shims on the compression side eliminate the risk of cavitation, and
the shims on the rebound side works as a check valve.
External
adjuster
The external
adjuster, easy to reach on the piston shaft just above the eyelet, fig.
3, is connected to the main bleed valve via an aluminium rod that runs
inside the piston shaft. When the temperature in the damper increases the
rod expands keeping the flow through the valve exactly the same at all
working temperatures.
The adjuster moves the needle in the main bleed, which determines the orifice
size of path 3, fig. 1, 3, described in "How the shocks work".
When the adjuster knob is turned all the way clockwise to the closed position
the shock is most restrictive to rebound movement, rebounding slowest.
This adjustment has the greatest effect on the rebound damping, but it
also has an effect on the compression damping at a ratio of approximately;
10% compression and 90% rebound.
This position is the starting point for counting out the clicks (in an
anti clockwise motion) to the recommended adjuster position, normally 8-25
clicks.
Making adjustments
We will not try
to give any general rules of what to do with the shocks when you have a
specific handling problem since the suspension of a car is influenced by
so many things, springs, roll bars, tires, anti squat/dive and so on.
To make improvements, it is important that you learn how the shocks affect
the handling of your car, see below. Understanding its function and then
track testing does this.
When making adjustments, keep notes, make adjustments one at a time and in small steps (for example 2 clicks at a time) and when you think you have made an improvement go back to what you started with and double-check to be sure
Options
(all)
Double digressive
piston:
This piston can
produce high forces at low speed while maintaining a level slope at high
speeds.
High frequency
piston:
Excellent for
traction and grip on flat tracks.
One way shaft
jets:
Allows the compression
bleed to be smaller than the rebound bleed.
Parallel compression
valve:
Allows the rebound
bleed to be smaller than the compression bleed and makes it possible to
produce double-knee curves.
WCJ, MCJ only
Base plate and
jets:
Makes the shock
more responsive, smoother, safer and eliminates the risk of cavitation
without the need of increased gas pressure.
STJ only
External adjuster
kit:
Complete kit
to convert a non-adjustable shock to an adjustable model.
| Type | Extended
Length inches |
Compressed
Length Inches |
Stroke
Inches |
Body
Length Inches |
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Adobe
Acrobat Reader
WCJ
Racing Manual
This manual contains the text shown on this web page as well as demonstrates how to revalve WCJ shocks. File Size: 3.4 MB, 16 Pages. Use paper orientation "Portrait" and "Fit to page" when printing. download |
| Shock
Adjustment Guide
Learn how to adjust your shocks for different racing conditions. File Size: 112 kB, 1 Page. Use paper orientation "Portrait" and "Fit to page" when printing. download |
X-Stack
Manual
 File Size:1452 kB, 8 Pages. Use paper orientation "Portrait" and "Fit to page" when printing. download |
| Compression stroke |
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| 1. The oil flow in the shock absorber body during a compression stroke. |
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| Rebound stroke |
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| 2. The oil flow in the shock absorber body during a rebound stroke. |
3. The external
adjuster affects both rebound- and compression damping.
