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ROYAL ENFIELD 350cc and 500cc O.H.V. WORKSHOP MANUAL
Units having Part No. 36451 have a spring
of .264in. diameter wire (Part No. 35494)
having a rating of approximately 250lb. per
inch. The free overall length of both types of
spring is 7.3/4 in. New springs should be
fitted if they have set more than 1/8 in.
This type of suspension unit was fitted on
"350 Bullet" and "500 Twin" Models up to
the early part of the 1954 season, and on the
"250 Clipper" Model up to the later part of
the 1954 season.
To dismantle the unit, remove it from the
machine, grip the lower end of the bottom
casting in a vice, unscrew the top cover tube,
place a suitable bar through the Silentbloc
bush in the top casting and turn so as to
unscrew the spring from the scroll on either
the top or bottom casting. The top casting with
the inner main tube (which is brazed into it)
and the oil seal can now be withdrawn from
the outer main tube and bottom casting.
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If the spring has remained attached to the
bottom casting, unscrew the bottom cover tube
and unscrew the spring from the scroll on the
bottom casting, if necessary tapping it with a
hammer and a blunt chisel. The outer main tube
is brazed into the bottom casting and the
hollow damper post is brazed into the main
tube.
Oil tightness of these units depends on the
condition of the edge of the oil seal which must
be handled with great care. The synthetic rubber
seal is bonded to a hollow metal plug which
forms the valve port in the hydraulic damping
system. If the oil seal needs renewing the
easiest way to remove it from the inner main
tube is to pass a 13/32 in. diameter bar through
the hollow plug to prevent it closing in, then
grip the oil seal in a vice, pass a bar through the
eye in the top casting and pull and twist to
withdraw the hollow metal plug from the end of
the main tube. Take care not to damage the new
seal when fitting it.
After reassembling, remove the oil filler and
level plugs and fill with one of the following
oil, until it runs out through the level plug
orifice:
Castrolite;
Vacuum Arctic ;
Shell X-100. 20/20w; Essolube 20;
B.P. Energol S.A.E. 20.
Wait till the oil has ceased running, then
replace the oil filler and level plugs.
(c) Royal Enfield Units. Mark II. Enfield
rear suspension units, Part No. 38109, are
shown in Fig. 4. This type provides positive
damping on the rebound stroke and in
consequence does not need the spring to be
anchored on scrolls. The range of movement is
greater than the Mark I dampers and on account
of this and the improved damping the ride is
better, particularly on extended rough sections.
The spring rate is 150 lb. per inch.
This type of unit was fitted on the "Meteor
700" model up to the early part of the 1954
season and on the "500 Bullet" model up to the
later part of the 1954 season.
The Plunger Head contains a disc valve
which on the bump stroke provides only a slight
restriction to passage of oil between the inside
of the bottom bearing tube and the damper
chamber which is bounded by the inside wall of
the upper end of the bottom bearing tube, the
outer wall of the lower end of the top bearing
tube, the upper surface of the plunger head and
the lower end of the bearing bush. Since there is
not room in the damper chamber for all the oil
displaced on the bump stroke, provision is made
for the surplus to pass up the inside of the top
bearing tube and into the hollow top end
casting.
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