Stainless-steel alloys are today
found on motorcycles mainly in the
form of exhaust valves and exhaust
systems. So well-adapted to their
purpose have these alloys become
that there is no longer even a mem-
ory of the exhaust-valve problems
that plagued early motoring.
Records of racing at England’s
great Brooklands Speedway show
exhaust-valve failures as third-most-
frequent behind drive-belt and
spark-plug trouble. The chauffeurs
of moneyed early motorists at-
tended mandatory service schools,
learning to regrind valve seatings
every six weeks to restore the seal
steadily destroyed by intense heat
and corrosion.
Early engines were given exhaust
valves riveted together from a cast-
iron head—they make stoves out
of iron, right?—and a carbon-steel
stem. Seeking some better solu-
tion, engineering pioneer Frederick
Lanchester devised a single-valve
system, functioning alternately as
intake and exhaust, as a means
of cooling the hard-worked metal.
When the machine-tool industry
developed so-called tungsten “high-
speed steel” cutting tools, which
remained hard even when red
hot, they were eagerly adopted as
exhaust-valve materials.
Yet valves went right ahead grad-
ually losing seal from corrosion,
stretching from high temperature
and strong valve springs, and being
a continuing menace to reliability.
Help was on the way. In England,
Harry Brearly—seeking more corro-
sion-resistant materials for gun-bar-
rel manufacture—discovered in
1913 that alloys of iron with at least
10.5 percent chromium displayed
greatly enhanced resistance to the
erosion of hot-propellant combus-
tion. Chromium reacts with the
oxygen in air to form a continuous
and strongly bonded surface layer/ ELEMENTS /
TOUGH
AND PURE
Stainless Steel has the power to resist
By KEVIN CAMERON / Photography by TIM SUTTON
S
of chromium oxide, a ceramic. This
layer protects the iron from oxida-
tion. Victory!
From Brearly’s work quickly
evolved the food-grade stainless
alloy known to this day as “18-8.”
Those numbers, seen on tableware
and cookware, indicate the pres-
ence of 18 percent chromium and 8
nickel in the material. Today, stain-
less flatware has almost completely
displaced actual silverware—and
the weekly ritual of polishing it.
By 1923, research had produced
a stainless exhaust-valve alloy
familiar to all fanciers of older
British motorcycles: KE965. It had
the remarkable property of being
compatible with fuels containing
the anti-knock catalyst tetraethyl
lead—now banned from motor gas-
olines because it poisons catalytic
mufflers...and also people.OPPOSITE: Here are tube bends in stainless
steel, ready to become parts of an exhaust
system. It’s comforting to know they will
not in time become masses of rust.22 / CYCLE WORLD