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Compression Stroke; Extension Stroke; Bearing Wear, Damage; Bearing Lubrication - Kawasaki KZ400 Service Manual

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Table of Contents
MAINTENANCE-CHASSIS
207
Table J15
Bearing Ball Specifications
I
I
Size
I
Quantitv
I
Steering stem warp
Examine the steering stem, and replace i t i f i t i s bent.
Upper
Lower
Bearing wear, damage
Wipe the bearings clean o f grease and dirt, and ex-
amine the races and balls. I f the balls or races are worn,
or i f either race is dented, replace both races and all the
balls for that bearing as a set.
Bearing lubrication
In accordance with the Periodic Maintenance Chart
(Pg.
lo),
and whenever the steering stem i s disassem-
bled, the steering stem bearings should be relubricated.
Wipe all the old grease o f f the races and balls, washing
them in a high flash-point solvent
if
necessary. Replace
the bearing parts i f they show wear or damage. Apply
grease liberally to the upper and lower races, and stick
the bearing balls in place with grease.
%"
%"
A. Bearing Race
B. Grease.
19
20
Grease seal deterioration, damage
Inspect the grease seal for any signs o f deterioration
or damage, and replace i t i f necessary.
Replace the grease seal with a new one whenever i t
has been removed.
FRONT FORK
Front fork consists o f the fork legs connected to the
frame head pipe by the stem base and stem head brack-
et.
I t accomplishes shock absorption through spring
action, air compression in the inner tube, and resistance
to the flow o f the oil forced into the cylinder by tube
movement.
Each fork leg i s telescopic tube including an inner
tube
7 ,
outer tube
8),
cylinder and piston unit
6
,
collar
Q ,
and cylinder base
14.
The inner tube fits into the
outer tube, altering its position in the outer tube as
the tube arrangement absorbs shocks. The cylinder is
fixed t o the bottom o f the outer tube and the piston
(equipped with a piston ring
5 )
is secured t o the top
o f the cylinder. The collar (coupled with a non-return
valve
17
),
fixed in the lower end o f the inner tube,
forms the upper part of the lower chamber and together
with the piston helps seal the upper chamber. The collar
and cylinder base configuration function t o form an oil
lock at the end o f the compression stroke t o prevent
the inner tube from striking the bottom. Small orifices
in the upper part o f the cylinder bring about an oil lock
at the end o f the extension stroke to prevent the inner
tube from striking the top.
Compression Stroke
Whenever a load i s placed on the front fork and
whenever the front wheel receives a shock, the inner
tube
7
moves down inside the outer tube
8
,
or the
outer tube moves up, compressing both the spring
4
and the air in the inner tube.
A t the same time, low
pressure (suction) i s created in an enlarging chamber
(upper chamber
9
)
formed between the inner tube and
the cylinder
6,,
and oil i s drawn in from a diminishing
chamber (lower chamber
13
)
formed between the outer
tube and the cylinder. As the lower chamber shrinks
in size with oil passing freely through the non-return
valve
17
into the upper chamber, oil also passes freely
through the cylinder lower orifices into the cylinder as
the inner tube approaches the cylinder base
14.
Near
the end of the compression stroke, the clearance be-
tween the tapered-out cylinder base and the collar
12
at the lower end o f the inner tube approaches zero.
The resulting resistance to the flow o f oil through this
small space slows the movement, finally forming an oil
lock t o finish the compression stroke.
Extension Stroke
Following the compression stroke
i s
the extension
stroke, in which the compressed spring extends to push
the inner tube back out o f the outer tube. As the tubes
move apart, the upper chamber grows smaller, forcing
the oil through the way i t came through the non-return
valve. These small holes restrict the oil flow into the
inner tube damping fork extension. Near the end o f the
extension stroke both the cylinder spring and the ar-
rangement o f the cylinder upper orifices provide further
resistance to extension.
As the collar rises, reducing
orifices are eliminated and an oil lock forms, finishing
the extension stroke.

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