Royal Enfield 500 TWIN 1949 Workshop Maintenance Manual page 71

ROYAL ENFIELD WORKSHOP MANUAL
Upward movement of the wheel spindle forces oil
from the lower chamber "A" through the annular
space between the spring stud (38067) and the bore of
the main tube valve port (38138) into the damper
chamber "B." During this stroke the pressure on the
underside of the valve plate (38073) causes this to lift
so that oil can also pass from "A" to "B" through the
eight holes in the valve body. Since, however, the
diameter of chamber "B" is less than that of chamber
"A" there is not room in "B" to receive all the oil
which must be displaced from "A" as the fork
operates. The surplus oil passes through the cross hole
in the spring stud and up the centre hole in the stud,
spilling out through the nut (38076) which secures the
upper end of the spring stud to the bronze guide at the
lower end of the fork spring.
On the rebound stroke the oil in the damper
chamber "B" is forced through the annular space
between the spring stud and the bore of the main tube
valve port. During this stroke pressure in chamber
"B" closes the two disc valves at the upper and lower
ends of the chamber so that the only path through
which the oil can escape is the annular space between
the spring stud and the port. Damping on the rebound
stroke is therefore heavier than on the bump stroke.
At the extreme end of either bump or rebound stroke
a small taper portion on the spring stud enters the
bore of the valve port, thus restricting the annular
space and increasing the amount of damping. At the
extreme end of the bump stroke the larger diameter
taper on the oil control collar (38075) enters the main
counterbore of the valve port thus forming a hydraulic
cushion to prevent metal to metal contact.
Section J1 Page 2
3. Dismantling the Fork to Replace Spring, Oil
Seal or Bearing Bushes
Place the machine on the centre stand, disconnect
the front brake control and remove the front wheel and
mudguard complete with stays. Unscrew the bottom
spring stud nut (38080) which will allow oil to run out
of the fork down to the level of the cross hole in the
spring stud. Now knock the spring stud upward into
the fork with a soft mallet, thus allowing the
remainder of the oil to escape. Pull the fork bottom
tube down as far as possible, thus exposing the oil
seal housing (38157). Unscrew this housing either by
mean of a spanner on the flats with which it is
provided or by using the gland nut handgrips
(E.5417). The bottom tube can now be withdrawn
completely from the main tube, leaving the bottom
tube bush, oil seal housing and oil seal in position on
the main tube.
Now unscrew the main tube valve port using "C"
spanner (E5418). The spring stud and spring can
now be withdrawn from the lower end of the main
tube.
The steel main tube bush (38156) can now be
tapped off the lower end of the tube, if necessary
using the bottom tube bush for this purpose. Before
doing this, however, it is advisable to mark the
position of the bush with a pencil line so as to ensure
reassembling it in the same position on the main
tube. The reason for this is that these bushes are
finish ground to size after fitting on to the tubes so as
to ensure concentricity. After removal of the main