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Page 6
Royal Enfield "Interceptor" Workshop Manual
Engine Specification
1.
Engine
The engine is an even-firing vertical twin-
cylinder, having separate cylinders and heads and
fully enclosed pressure-lubricated overhead valve
gear.
It
has a dry sump lubrication with the oil
tank integral with the crankcase and a massive one-
piece high-strength spheroidal graphite 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.
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
7l
mm, the stroke being 93 mm.
The
cubic capacity of the engine is 736 c.c.
The
cylinder heads are located on the cylinders by
hollow dowels and the joint between head and
barrel is made by a split, triangular section steel
ring which seats on a chamfer at the top end of the
cylinder barrel and stands about ·005 in. proud of
the joint face. The push rod tunnels are sealed
by washers of special heat and oil resistant rubber
bonded to metal and fitting in recesses in the
cylinder head.
4.
Pistons
The pistons are made of low expansion alu-
minium alloy, heat treated and form ground taper
and oval. Standard and low compression pistons
are available; the former having approximately
½
in. dome and
the
latter about
fir
in. Each piston
carries two compression rings, of which the top
one is chrome plated.
Standard compression
pistons are fitted with a special dual oil control
ring.
Low compression pistons use a single
slotted type ring.
Compression ratios are as follows:-
Standard Pistons, No compression plate-
8½
to 1.
Standard Pistons, I compression plate-
8 to I.
Standard Pistons,
2
compression plates-
7½
to 1.
Low Compression Pistons, no plate-
7¼
to
1.
Low Compression Pistons, 1 plate-6·9 to I.
Low Compression Pistons, 2 plates-6·6 to 1.
5.
Connecting Rods
The connecting rods are produced from stamp-
ings 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, the heads of
which are drilled for wiring.
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
spheroidal graphitic cast iron. The total weight is
approximately 24 lbs., and all 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 is drilled through its
centre for 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.
Alternative cam-
shafts with quietening ramps are available for
riders who are prepared to sacrifice a little per-
formance in the interests of mechanical silence.
These were fitted to the earlier engines.
The camshafts are located in the crankcase and
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