Royal Enfield 350 BULLET 1949, Workshop Maintenance Manual

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ROYAL ENFIELD WORKSHOP MANUAL
housed in a box bolted to the frame behind the
carburettor.
16. Lubrication System
Lubrication is by the Royal Enfield
Dry-Sump which is entirely automatic and
positive in action.
The oil tank is integral with the crankcase,
ensuring the full rate of circulation immediately
the engine is started and rapid heating of the oil
in cold weather.
There are two piston type oil pumps running
at 1/12 engine speed, positively driven from the
timing side engine shaft through a worm gear.
The feed pump at the rear of the timing cover
is for pumping oil from the tank to the big end
bearing. This oil drains to the bottom of the
crankcase and is pumped by the return pump
back to the tank.
Some of the return oil is by-passed to the
cylinder head for lubricating the rocker gear,
whence it flows down the push rod tunnels to the
timing chest.
From here it is returned to the tank by the
two idler pinions in the timing drive which act as
a gear pump.
The return pump has a capacity of approxi-
mately double that of the feed pump, which
ensures that oil does not accumulate in the
crank-case.
Both pumps are double-acting, but the two
sides of the feed pump are interconnected,
thereby giving an augmented and more even
supply to the big end. Both sides of the return
pump are also interconnected for draining the
crankcase.
Separate spring-loaded relief valves control
the pressure to the big end and to the valve gear.
The oil supply to the big end is through
internally drilled passages and that to the valve
gear is through an external pipe.
Gauze strainers are provided for the feed oil
leaving the tank and for the return oil from the
crankcase. In addition, the feed oil to the big end
is pumped under pressure through a large
capacity felt filter.
An important feature of the design of this
filter is that the internal arrangement is such that,
should it be neglected and become clogged, the
oil pressure will lift the spring and cap off its
Seating thereby automatically by-passing the
filter so that the big end will not be deprived of
lubrication, even though the oil may be dirty.
17. Breather
The efficient operation of the breather is of
paramount importance to the performance of the
engine because it acts as a non-return valve
between the crankcase and the outside
atmosphere, causing a partial vacuum in the
crankcase and rocker boxes which prevents the
passage of oil into the cylinder and consequent
smoking and oiling of the plug.
On the 500 c.c. engine the breather is located
on the driving side of the crankcase and consists
of a small housing containing two pen-steel
discs covering two holes drilled in the
crankcase.
Accurate seating of the discs is ensured by a
pen-steel plate held between the breather body
and the crankcase.
On early 350 c.c. engines the breather
consists of a disc in the engine sprocket securing
nut. On later engines there is a fibre disc located
in a small housing mounted on the crankcase
immediately behind the magdyno.
18. Gearbox
The gearbox is bolted on to the back of the
crankcase and has four speeds, which are foot
controlled, and a patented neutral finder. All
gears are in constant mesh, changes being
effected by robust dog clutches.
The standard gear ratios are as follows:
350 c.c. Solo 5.67, 7.37, 10.20, 15.75 to 1.
500 c.c. Solo 4.91, 6.40, 8.85, 13.65 to 1.
500 c.c. Sidecar 5.72, 7.45, 10.30, 15.90 to 1.
19. Clutch
On the "500 Bullet" the clutch has five
pressure plates and five friction plates, including
the sprocket which is lined on both sides with
friction material. The other friction plates have
cork or "Klinger" inserts which give smooth
operation and freedom from slipping in the
presence of oil. The clutch centre is fitted with
shock absorbers consisting of rubber blocks.
The clutch on the "350 Bullet" is similar to
that described above except that it has four
pressure plates and four friction plates, and the
clutch centre is solid.
350 BULLET OIL PUMP DIAGRAMS
FEED PUMP FEED PUMP
POSITION 1 POSITION 2
The ports in the housing are connected as follows
X - delivery to big end.
Y - suction from oil tank
Z - suction from oil tank
Position 1. The plunger A is being drawn out
of the cylinder hole in the disc C by the action of
the peg B on the shaft D. The port T in the disc C
registers with the suction port Y in the housing,
so that oil is drawn into the cylinder from the oil
tank. At the same time the port U in the disc
registers with the delivery port X in the housing,
so that oil blow the disc in the housing is forced
through U and X to the big end.
Position 2. The plunger A is being pushed into
the cylinder hole in the disc C. The port T in the
disc now registers with the delivery port X in the
housing, so that oil is forced out of the cylinder
to the big end. At the same time the suction port
Z in the housing is uncovered by the disc and oil
is drawn into the housing below the disc from the
oil tank.
RETURN PUMP RETURN PUMP
POSITION 1 POSITION 2
The ports in the housing are connected as follows
X' - delivery to rocker gear
Y - suction from crankcase.
Position 1. The plunger A' is being drawn out
of the cylinder hole in the disc C'. The port T' in
the disc registers with the suction port Y' in the
housing, so that oil is drawn into the cylinder
from the crankcase sump at the same time the
port U' in the disc registers with the delivery port
X' in the housing, so that oil below the disc in the
housing is forced through U' and X' to the rocker
gear.
Position 2. The Plunger A' is being pushed
into the cylinder hole in the disc C. The port T'
now registers with the delivery port X' in the
housing, so that oil is forced out of the cylinder
to the rocker gear. At the same time, the port V'
in the disc registers with the suction port Y' in the
housing, so that oil is drawn into the housing
below the disc from the crankcase sump through
V' and Y'.
Section B2 Page 4
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