BOMBARDIER 1996 Ski-doo MX Z440 Handbook page 53

dampening. By varying the number and thickness of shims the dampening characteristics can be
very accurately obtained. There may also be orifices or "slits" in the piston that are not covered by
the shims. These are referred to as bleed slits. The size and number of these slits will also affect
dampening. The external adjustment on the MVA, HPG shocks is a variable bleed hole.
Rebound dampening will usually be much stiffer than compression dampening. This is because
rebound dampening must resist the force of the spring and because piston speeds are much
slower during rebound.
At low piston speeds, the number of bleed slits will have a fairly large effect on dampening, but as
piston speeds increase most of the dampening is controlled by the shim stack. This is because the
flow area of the slits is much smaller than the flow area under the shims. Since only a small
amount of oil can flow through the bleed slits (compared to the amount that flows under the shim
stack), the slits have only a very small effect on dampening at high piston speeds. Because of this
characteristic, bleed slits are most effective on rebound dampening. They will have only a very
slight effect on compression damping because the typical piston speeds on compression strokes
are several times faster than on rebound strokes. There really is no such thing as "high speed"
rebound dampening.
Dampen
force
o
o
As mentioned earlier, the configuration of the shim stack will control most of the dampening of the
shock. There are several methods to tuning shim stacks. The first and most commonly used is to
increase or decrease the overall stiffness of the stack. This can be done by changing the number of
large shims or by increasing or decreasing their thickness.
EFFECT OF BLEED SLITS
Rebound
Piston speed
No bleeds
2 bleeds
4 bleeds
6 bleeds
Dampen
force
o
n
u
Compression
Piston speed
03-37