On the rebound stroke the disc valve in the
plunger head closes under pressure in the
damper chamber, so that the oil is forced past
the clearance between the plunger head and
the inside wall of the bottom bearing tube,
thus providing positive damping on the
rebound stroke.
At the end of the bump stroke the Oil
Damping Post enters the open end of the top
bearing tube thus providing a hydraulic
cushion to prevent bottoming.
top bearing tube and plunger head from the
bottom bearing tube, bottom casting and outer
tube assembly.
The spring can now be lifted away. Its
original free length is 8.3/4 in. If it has closed
more than 1/8 – 3/16 in. a new spring should be
fitted.
If it is required to renew the bearing bush or
oil seal, the plunger head must be dismantled by
unscrewing it from the top bearing tube and then
lifting away the Oil Control Valve and circlip,
the top bearing assembly comprising the oil seal
and bearing bush in a housing can now be
withdrawn from the lower end of the top bearing
tube. The oil seal and bearing bush are secured
in the housing by spinning over the end of the
latter. A new assembly must therefore be fitted if
either oil seal or bearing require renewing.
After reassembly of the plunger head, fill the
bottom bearing tube with oil of one of the grades
given below. Remove the oil filler screw from
the top casting, replace the spring, and carefully
insert the plunger head into the bottom bearing
tube, pushing it down slowly so as to spill as
little oil as possible and allow time for oil to
enter the damper chamber and pass up the inside
of the top bearing tube. Tighten down the top
bearing and oil seal assembly with a thin spanner
inserted between the coils of the spring.
Now use a mandrel press or a vertical drilling
machine to compress the damper unit fully and
carefully insert oil through the filling orifice
until the unit is completely full. Slightly release
the pressure and then compress again fully
several times to remove air bubbles. Release the
pressure to allow the spring to expand about 1
in. before replacing the oil filler plug.
Use one of the following grades of oil:
Castrolite; Vacuum Arctic;
Shell X-I00 20/20w; Essolube 20;
B.P. Energol S.A.E. 20.
5. Removal of Swinging Arm Chain Stays
First remove one of the pivot pin nuts and pull
the pivot pin out from the other end. To release
the pivot bearing it is necessary to spread the
rear portion of the frame, using the frame
expander E.5431, which will spread the frame
sufficiently to enable the spigots on the thrust
washers to clear the recesses in the pivot lugs
forming part of the frame.
If it is necessary to remove the bronze bushes
these can be driven out by means of a hammer
and a suitable drift and new bushes can be fitted
under a press without difficulty. After fitting the
bushes they must be reamed to .844/.843 in.
6. Centre Stand
To remove the centre stand unscrew the nut
from one end of the stand spindle, knock out the
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