Section B4 - Royal Enfield CONSTELLATION 1958 Workshop Maintenance Manual

1. Engine
The engine is an even-firing vertical twin
cylinder, having separate cylinders and heads
and fully enclosed pressure-fed overhead valve
gear. It has dry sump lubrication with the oil
tank integral with the crankcase and a massive
one piece high-strength cast iron crankshaft.
2. Cylinder Heads
The cylinder heads are die-cast from light
aluminium alloy with ample finning to ensure
adequate cooling. The exhaust pipe inserts are
cast in and the valve inserts are of austenitic
iron and are shrunk in so that they are
replaceable. Steel wire thread inserts which are
easily renewable are provided for the sparking
plugs to prevent damage to the threads in the
heads. The large capacity induction ports are
streamlined and blended to the valve seatings.
3. Cylinders
The separate cast iron cylinders have a
nominal bore of 70 m.m., the stroke being 90
m.m. The cubic capacity of the engine is 692
c.c. The cylinder heads are located on the
cylinders by hollow dowels.
4. Pistons
The high compression pistons are of low
expansion aluminium alloy, heat treated and
form-turned oval and having split skirts. The
compression ratio is 7¼ 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 Rods
The connecting rods are produced from
stampings of Hiduminium RR56 light alloy. The
little end bearings are of alloy direct on to the
gudgeon pin. In case of wear after long service
the little end can be bored out and fitted with a
bush, but this is rarely necessary.
The big end bearings are of alloy direct to the
crankshaft. The detachable bearing caps are

SECTION B4

Engine Specification
" Super Meteor "
bolted to the connecting rods by means of high
tensile socket screws, secured by cotter pins.
6. Crankcase
The combined crankcase and oil tank is
die-cast from light alloy in two halves, being
split vertically.
7. Crankshaft and Flywheel
The crankshaft is cast in one piece, integral
with the massive central flywheel, from high
quality meehanite cast iron. The total weight is
26lbs. and it is carefully balanced.
The main journals are ground and the big end
journals are ground and hand-lapped.
8. Main Bearings
Heavy duty bearings are provided for the
crankshaft, the driving side being ball and the
timing side roller.
9. Camshafts
The camshafts are machined from drop
forged steel stampings with the cams and
bearings hardened and ground. The cam profiles
are produced with silencing ramps to ensure
quiet running.
10. Valves
The inlet valves are machined from
stampings of special Silicon-Chrome Valve
Steel and the exhaust valves are of austenitic
steel.
11. Valve Gear
The valves are operated from the camshafts
by means of large flat based guided tappets,
tubular alloy push rods and overhead rockers.
Two compression springs are fitted to each
valve.
12. Timing Drive
The camshafts are located in the crankcase,
running in bronze bushes. They are driven by a
common, endless chain from the timing
sprocket on the crankshaft and the tightness of
the chain can be adjusted by means of the chain
tensioner in the timing chest.
Section B4 Page 1