Royal Enfield 500 TWIN 1949, Workshop Maintenance Manual

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ROYAL ENFIELD WORKSHOP MANUAL
the scrolls). 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withdrawn from the outer main tube and bottom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. 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.
Section H1 Page 3
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