Section B3 - Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual

ROYAL ENFIELD WORKSHOP MANUAL
1. Engine
The engine is a 248c.c. vertical single four
stroke, with separate cylinder head and fully
enclosed pressure-fed overhead valve gear. It
has dry sump lubrication with the oil tank
integral with the crankcase and a built-up steel
crankshaft.
2. Cylinder Head
The cylinder head is of cast iron and is
generously finned to ensure adequate cooling. It
has a large bore induction port, stream-lined and
blended to the valve seating.
3. Cylinder
The cylinder barrel is of cast iron, with
internal tunnels enclosing the push rods. The bore
is nominally 64m.m. and the stroke 77m.m.,
giving a cubic capacity of 248 c.c.
4. Piston
The piston is cast from low expansion
aluminium alloy, heat treated and form-turned
oval and having a split skirt. The compression
ratio is 6½ to 1. There are three piston rings, the
top two of which are compression rings. Both are
taper ground and the top, one is chromium plated.
The third ring is for oil control and is slotted.
5. Connecting Rod
The connecting rod is machined from a
manganese-molybdenum steel stamping and has
a carobronze bush in the little end. The big end
has a hardened chrome steel bush pressed in and
a floating bush made from mild steel and white
metalled.
6. Crankcase
The combined crankcase and oil tank are
die-cast from light alloy in two halves, being split
vertically.
7. Crankshaft and Flywheel
The crankshaft is built up from two steel
flywheels bolted to the crankpin and bolted and
keyed to the engine shafts the whole being
carefully balanced.

SECTION B3

Engine Specification
250 Clipper
8. Main Bearings
Heavy duty roller bearings are provided for
the engine shafts, the outer races being shrunk
into the crankcase while internally the rollers run
direct on the shafts.
9. Cams
The cams are integral with the cam pinions
being machined from carbon steel and case
hardened. They have internal bronze bushes
running on fixed spindles in the timing chest.
The cam profiles are produced with silencing
ramps to ensure quiet running.
10. Valves
The inlet valve is machined from a stamping
of silicon-chrome valve steel and the exhaust
valve is of austenitic steel.
11. Valve Gear
The valves are operated from the cams by,
means of large flat based guided tappets, high
quality tubular steel push rods, with steel caps.
and overhead rockers. Two compression springs
are fitted to each valve.
12. Timing Drive
The cams are located in the timing chest and
are driven at half engine speed from the
crankshaft by a positive geared drive.
The contact breaker is driven from the inlet
cam pinion through two idler pinions which also
act as a gear pump to return the oil from the
timing chest to the oil tank.
13. Ignition and Lighting System
Coil ignition and lighting are supplied from a
6volt battery which is charged through a rectifier
from an A.C. alternator mounted on the engine
shaft inside the primary chain case.
The alternator has a permanent magnet rotor
revolving within a six pole wound laminated
stator.
The arrangement is such that in case of
battery failure, the ignition can be supplied direct
from the alternator.
Section B3 Page 1