Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 12

ROYAL ENFIELD WORKSHOP MANUAL
Earlier engines have Miller equipment and
more recent ones Lucas.
14. Carburettor
Amal Type 274/BS/3A. See Section F.1. or
Amal Type 375/10. See Section F.2.
15. Air Filter
The air supply to the carburettor is cleaned
by a Vokes Micro-Vee felt and gauze dry filter,
housed in a box bolted to the frame behind the
carburettor.
16. Lubrication System
Lubrication is by the Royal Enfield dry-
sump system 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 and to the cylinder wall. 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 there 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
approximately double that of the feed pump,
which ensures that oil does not accumulate in
the crankcase.
Both pumps are double-acting, one side of
the feed pump supplying the big end only, while
the other side pumps oil to the cylinder wall to
lubricate the back of the piston. Both sides of
the return pump are inter-connected for draining
the crankcase.
Separate spring loaded relief valves control
the pressure to the big end and to the valve gear.
The oil supplies to the big end and to the
cylinder wall are 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 end cap off
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
atmosphere, causing a partial vacuum in the
crankcase and rocker box which prevents the
passage of oil into the cylinder and consequent
smoking and oiling of the plug.
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.
18. Gearbox
The gear box is bolted on to the rear engine
plates and has four speeds, which are foot con-
trolled. All the gears are in constant mesh,
changes being effected by robust dog clutches.
The standard gear ratios are 6.25, 8.45, 13.1,
18.5 to 1.
19. Clutch
The clutch has three pressure plates and two
friction plates, one of which is the inner portion
of the clutch sprocket.
Both friction plates have cork inserts which
give smooth operation and freedom from
slipping in the presence of oil.
its seating thereby
and the outside
Section B3 Page 5