Royal Enfield 500 TWIN 1949 Workshop Maintenance Manual page 67

ROYAL ENFIELD WORKSHOP MANUAL
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.
To dismantle the unit, remove it from the
machine, grip the lower end of the bottom
casting in a vice and unscrew the top outer tube.
Now insert a thin spanner .820 in. across flats
between the coils of the spring to engage the
flats on the top bearing and oil seal assembly,
unscrew this and withdraw the top casting,
Section H1 Page 4
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bearing bush in a housing can now be withdrawn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;
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
Essolube 20;