Royal Enfield 250 CLIPPER, Workshop Maintenance Manual

Page: 66 / 96

ROYAL ENFIELD WORKSHOP MANUAL
PAGE 66
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 socket
nut which secures the upper end of the spring
stud to the bronze guide at the lower end of the
fork spring, thus providing a measure of damping.
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. Towards the 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 enters the main
counterbore of the valve port thus forming a
hydraulic cushion to prevent metal to metal
contact.
9. Dismantling the Fork to Replace Spring, Oil
Seal or Bearing Bushes ("250 Trials")
Place the machine on the centre stand,
disconnect the front brake control and remove the
front wheel and mudguard complete with stay.
Knock the rearmost cap stud upwards into the
fork with a soft mallet, which will allow oil to run
out of the fork. Pull the fork bottom tube down as
far as possible, thus exposing the oil seal housing
Unscrew this housing either by means of a spanner
on the flats with which it is provided or by using
the gland nut hand grips (E.4912). 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tube can now be withdrawn completely from the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 (E.5418). The spring stud and spring
can now be withdrawn from the lower end of the
main tube.
The steel main tube bush 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 tube bush the bottom tube bush, oil seal
housing and oil seal can be removed.
10. Reassembly of Parts
("250
Trials")
When refitting the oil seal, or fitting a new one,
great care must be exercised not to damage the
synthetic rubber lip which forms the actual seal. If
the seal has been removed from the upper end of
the main tube and is refitted from this end a
special nose piece (Fig. 6) must be fitted over the
end of the tube to prevent the thread from
damaging the oil seal.
The spring stud is a tight fit in the hole at the
lower end of the bottom tube. Once the stud has
been entered in the hole push the bottom tube up
sharply against the spring until two or three
threads on the stud project beneath the end of the
bottom tube. Now fit the nut and washer and pull
the stud into position by tightening the nut. If
necessary fit the nut first without the washer until
sufficient thread is projecting to enable the washer
to be fitted.
11. Steering Head Races and Removal of
Complete Fork ("250 Trials")
See Subsections 5 and 6.
12.
Lubrication
("250
Trials")
The lubrication of the fork bearings is effected
by the oil which forms the hydraulic damping
medium. All that is necessary is to keep sufficient
oil in the fork to ensure that the top end of the
bottom spring stud is never uncovered even in the
full rebound position. The level of oil in the fork
can be gauged by removing the top plug screw and
inserting a long rod about
3
/
8
in. diameter. If
slightly tilted this will ledge against the nut at the
upper end of the bottom spring stud and indicate
the level of oil above the stud. If the fork is empty
to start with the quantity required is approximately
7 ½ fluid ounces in each leg. Use one of the oils
recommended in Subsection 7.
J7
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