1965 Royal Enfield Interceptor - 4-Page Vintage Motorcycle Road Test Article

Description

1965 Royal Enfield Interceptor - 4-Page Vintage Motorcycle Road Test Article
Original, vintage magazine article
Page Size: Approx. 8" x 11" (21 cm x 28 cm) each page
Condition: Good
Most motorcycles have an indefinable something we
call “character,” and because they have this quality,
they also almost invariably acquire appropriate names.
We do not know what the average Royal Enfield Inter-
ceptor owner is calling his machine these days; but we
would offer “King Kong” as a suggestion. No other name
that comes to mind so completely describes the Inter-
ceptor: it is truly big and hairy. Of course, others have
the size, but none have the Interceptor’s sheer brute
performance. It is, by an impressive margin, the fastest
true road machine we have ever tested. Fast, in the sense
that it will reach 120 mph (we no longer make high-speed
runs with touring bikes, but the bike should pull 7000
rpm in 4th). Fast, too, in that it covers distance from a
standing start at a rate few others can approach. In full
road trim, without benefit of any on-the-spot tuning, the
Interceptor we tested would do the standing-start 1/4-mile
in an astonishing 13.8 seconds, with a terminal speed of
96 mph.
All of this is especially remarkable if one considers that
the Royal Enfield Interceptor is relatively heavy, and
pulls a relatively “tall” overall drive ratio with what its
makers say is only 52.5 bhp. In light of its performance, it
must be said that the Interceptor has a very healthy 52.5
bhp, and a lot of torque to back it up. As a matter of
fact, Enfield advertising stresses the torque, and gives
credit for this to the engine’s long stroke. We will certain-
ly agree that the engine has a long stroke — 3.66 inches
is a lot. However, as we have said before and say again
now, bore/stroke ratio has no direct bearing on an en-
gine’s torque characteristics. This is all a question of
carburetion, porting, valves and valve timing. Engines that
have a lot of low-speed torque usually have a stroke ap-
preciably greater than their bore size, but this is incidental;
the other factors we listed determine where the torque
peak will be. The Enfield engine will crank off revolutions
quite vigorously, if one considers the length of its stroke,
but the stroke is a limiting factor. On the other hand, the
long stroke gives lower bearing loads at low crank speeds,
and its natural partner, the small cylinder bore, gives a
compact combustion chamber, a light piston, and high
thermal efficiency. In the end, the Enfield’s long stroke
will limit power output; but, and this is very important,
within the speed range the average rider will use (up to
6000 rpm) the long stroke is no handicap whatever,
and it does have the advantages we noted. Finally, there
can be no disputing the fact that this engine does the job
with regard to performance, and we haven’t heard any
complaints about reliability.
Perhaps the reason we don’t hear of the Enfield en-
gine lacking reliability is because so much attention has
been given to making it strong. It has, for example, really
huge main bearings, and the crankshaft is cast all in a
single piece of nodular iron. Some people may sneer at
a cast-iron crankshaft; they shouldn't. Nodular iron is
not the brittle stuff that has gone into so many old engine
blocks. It has a molecular structure that gives it great
strength and fatigue resistance, and has proven entirely
satisfactory in a lot of applications where only forgings
could be used a few years ago. Also, it has the good wear-
ing properties of most cast irons, and journal life should
be exceptional. And, of course, it has the great advantage
of permitting the crank and flywheel to be made in a
single piece — something that is virtually impossible with
forgings.
Cast-iron (not nodular) is also used for the cylinders....
And much more!
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