Royal Enfield CONSTELLATION 1958, Workshop Maintenance Manual

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SECTION B11
Engine Specification
“Constellation”
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 stream-lined
and blended to the valve seatings.
3. Cylinders
The cylinders are separate and of cast iron,
with internal tunnels enclosing the push rods.
The cylinder heads are located by spigots on the
cylinder barrels.
The cylinder heads are located on the
cylinders by hollow dowels.
4. Pistons
The pistons are of low expansion aluminium
alloy, heat-treated and form-turned oval. The
compression ratio is 8 to 1.
Early models have three piston rings, the top
two being compression rings, the bottom one a
single slotted scraper. Later models have pistons
of lighter weight than earlier types, and whilst
retaining similar compression rings, the bottom
piston ring groove contains 2 separate oil
control rings (see Fig. 7, section C). All
compression rings are taper ground, the top one
being chromium plated.
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 consist of
white-metalled steel liners which are renewable.
The detachable bearing caps are bolted to the
connecting rods by means of high tensile socket
screws, secured by cotter pins.
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 cast in one piece, integral
with the massive central flywheel, from high
quality spheroidal graphitic cast iron. The total
weight is 24 lbs. and except in some earlier
engines the crankshafts are dynamically
balanced.
The main journals are ground and the big end
journals are ground and hand-lapped. The main
journal on the drive side of the later type
crankshaft is drilled through its centre for the
situation and operation of the crankcase breather.
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 to give racing performance and, in
order to obtain the maximum efficiency, the
usual silencing ramps are omitted.
The camshafts are located in the crankcase
and run in bronze bushes. The bushes on the
near side are pressed into detachable housings
which are bolted to the driving side crankcase.
This enables the camshafts to be changed, if so
desired for tuning purposes, without the
necessity of dismantling the crankcases.
10. Valves
The inlet valves are machined from
stampings of special Silicon-Chrome Valve
Steel and the exhaust valves are of High
Nickel-Chromium Tungsten valve Steel with
the stems stellite-faced.
Section B11 Page 1
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