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Page 6
Royal Enfield "Interceptor" 750 Series II Workshop
1vf
anual
Engine Specification
1.
Engine
The engine is an even-firing vertical twin-
cylinder, having separate cylinders and heads and
fully enclosed overhead valve gear. The oil is
carried in a sump at the bottom of the crankcase
and is pressure fed to big ends and valve rockers.
A
massive
one-piece
high-strength
spheroidal
graphite cast iron crankshaft is used.
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 71 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 ~t 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. Each piston carries two taper faced
compression rings and a special dual oil control
ring.
One compression plate, .022 in. thick, is fitted
below each cylinder barrel when the compression
ratio is 8.5 to I. With the plates removed the ratio
is raised to 9 to I.
·
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 Flvwheel
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 crankshaft5 are
dynamically 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 camshafts are located in the crankcase and
run in bronze bushes in the left hand case and in
detachable aluminium housings which are bolted
to the timing side crankcase. This enables the cam-
shafts to be changed, if so desired for tuning
purposes, without the necessity of dismantling the
crankcase.
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-tipped.
11.
Valve Gear
The valves are operated from the camshaft by
means of large, flat-based, guided tappets, tubular
alloy push rods with induction hardened steel ends
and overhead rockers. Two compression springs
are fitted to each valve secured by Bullock Type
split collets locking in high strength aluminium
collars. The springs are specially designed to give
a variable rate on compression.
12.
Timing Drive
The camshafts are driven by an 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.
An extension of the front camshaft drives the
contact breaker housed in the timing cover.
A tachometer gearbox is mounted on the left
hand crankcase and is driven by the fro,nt camshaft.
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