Shaving Weight
CW SPECIALITY FILE
Shaving Weight
Titanium is less than halt the weight of steel, but is it worth the price?
KEVIN CAMERON
TITANIUM IS FASHIONABLE, expensive, almost too good to be true. Titanium is two-fifths lighter than steel, develops equal strength and has a higher melting point. Its iridescent sheen is beautiful-more brilliant than the calm luster of stainless or nickel steel. Titanium is jewelry. In the hand, its lightness is almost alarming. It epitomizes technology and exclusivity. Ducati 916 owners can’t resist titanium’s special aura any more than engineers can resist its physical properties.
Titanium the element was discovered 200 years ago by a German chemist, but was not isolated in analyzable quantity until 1925. Titanium in quantity is a child of the Cold War.
The Berlin Blockade, the Soviets’ first nuclear bomb test in August 1949, and the beginning of the Korean war in 1950 were its parents. To engineers faced with problems of stress and weight in suddenly essential new turbojet aircraft engines, titanium was a gift-light, strong, enduring. In 1948, U.S. titanium production was 3 tons, but by 1957 it had expanded 10,000 times. By 1953, Canadian jet-maker Orenda was ready to gamble its entire PS-13 supersonic engine program on titanium. General Electric wasted no time putting the wonder-metal into its jets, first the J53, later the hugely successful J47. Titanium was flying.
Jack Williams came to AJS/Matchless in 1954, from three years in the aircraft industry. Williams tested titanium rocker arms and connecting rods during his brilliant development of the 7R 350cc Single race engine. Phil Irving, the engineer behind the legendary Vincent, publicized the new metal. Norton tested rods of titanium D.T.D. 5053 in its factory race engines. When bearing magnate Tony Vandervell hired Polish engineer Leo Kuzmicki away from Norton to develop his Vanwall GP car engine, it too sprouted Ti rods.
Titanium’s high cost is in manufacturing. When melted, it avidly absorbs gases that embrittle it, so all hot processing must be carried out under vacuum. Titanium can be forged, rolled and formed, but it must be done carefully. After hot work, the outer layer, with its crippling load of dissolved gases, must be etched or ground away. Machining it required new techniques. Tricky stuff.
The payback is strength, lightness and long fatigue life. Titanium alloy 6A1 4V (6 percent aluminum, 4 percent Vanadium) can develop 160,000-psi tensile strength-equal to that of normal high-strength steels-at only 57 percent of the weight. Advanced alloys offer strength to 250,000 psi. Weight saving is attractive, but for parts under inertia load, the payback is huge: The lighter weight reduces inertia force, which in turn cuts stress. Centrifugal-loaded turbojet compressor blades and discs were the application that drove governments to fund titanium production-and connecting-rods and valves likewise drew piston-engine designers to the new material. A titanium conrod can tolerate the same load as a steel one, but its own lighter weight lightens inertia loads
on cranks and bearings. Titanium valves and rockers require less spring to follow cam profiles.
Once available in quantity, titanium was next applied as a structural material. Lockheed chose titanium as primary structure for the Mach 3-plus SR-71 Blackbird, revealed in 1964. In the 1960s, BSA had a tough, titanium tubular chassis built for its 441 Victor motocrosser. Honda quietly used U.S. titanium in its classic four-stroke road-
racers of the 1960s. Racers eagerly sought titanium from any source. Indiana roadracer Bob Wakefield made titanium rods for his Kawasaki Al-R in 1968, and others would follow his example. In the scramble, some tried to make heavily loaded parts from the soft, corrosion-resistant grades used in the chemical industries. The parts failed. Race sanctioning bodies responded predictably-with a ban.
During the 1970s, Kawasaki and Porsche, among others, tried titanium as cylinder studs (heat expansion differences broke them) and brake caliper pistons. Porsche put Ti rods in racecars and some street 935s. Ti valves required stem coating to prevent destructive scuffing, and conrod big-ends needed surface treatment to survive side-thrust friction.
As turbojet engineers had discovered, motor-racing designers found that parts had to be designed to be made in titanium from the beginning. Simply changing material in an existing design was poor engineering. Suzuki learned this the hard way in the mid-1970s, as did many others.
Although titanium can be
strong, it’s Young’s modulus, or “spring constant,” is half that of steel. Therefore, although titanium can carry the load, it deforms more in doing so. In 1981, national racer Nick Richichi had a titanium front axle made for his Yamaha TZ750, but went straight back to steel after one track test; he could feel increased front-end flex. Simple substitution wasn’t enough to realize titanium’s advantage. To reach or exceed the stiffness of the small-diameter solid steel axle, the titanium one should have been made as a large tube-like the axles on the Britten Twin.
When Honda returned to U.S. roadracing in 1980, its 1025cc Superbikes and F-l
racers used forged rods from Jet Titanium, and titanium valves. When crew chief Udo Gietl asked race manager Steve McLaughlin for one set of the expensive valves, he was grandly directed to order a hundred. In the late 1980s, 500cc GP bikes began to use titanium pipes, and four-stroke pipes came soon. Titanium crank wheels have at least been tested in racing. The late John Britten chose Cosworth titanium rods and Del West titanium valves with tiny, slender stems for his V-1000 Twin.
Today, many suppliers offer ranges of titanium fasteners, axles, pivots and bracketry for popular sportbikes. Titanium conrods are
available from forging or billet. Titanium four-stroke exhaust pipes, so stunningly light, have displaced stainless pipes on racebikes. Welding oxide layers present to the eye the most beautiful gradations of color upon color in these pipes. A word of caution: Above 1310 degrees F, titanium converts to a flaky yellow oxide; don’t heatwrap titanium pipes!
Titanium also should not be used against cadmium-plated washers or nuts because embrittlement results.
Though titanium is often chosen for high-stress applications, Rob Muzzy for one insists that the rods and valves in his Superbikes are the steel factory race-kit parts-and that Ti parts offer no gain. Its use in fasteners and pivots requires thought, too. Weigh your pieces, take two-fifths of that weight and ask yourself if titanium’s bill is worth the number of grams saved. Are technology and expense identical? Twenty years ago, Porsche used $ 100 per pound as the ceiling cost for weight savings. Your figure may differ, and times have changed. Besides, titanium is beautiful. Don’t people pay millions for a Van Gogh?
