In the spring of 1971, we had two premature crankshaft failures in our dealership's two-stroke 500cc Kawasaki H1R roadracer. In 1970, cranks typically lasted 600 to 800 racing miles, which was excellent at the time (during the recent era of Honda CBR600RR-spec engines in Moto2, those modern four-stroke engines were given new cranks and connecting rods after every three GPs).

But in our first 1971 outings, we had seizures of con-rod big-end needle bearings at roughly 150 and 300 miles. We would soon learn that Ginger Molloy, running the same machine, had one rod bearing seize at 49 miles! Ginger was a very experienced two-stroke rider/tuner, having ridden his self-tuned H1R to second behind Giacomo Agostini in the 1970 500cc world championship.

When I phoned the US distributor about this, I was referred to a tech who told me, “It must be something you’re doing wrong because we haven’t had a single failure.” Years later, I would be anonymously sent a copy of a January 1971 telex from racing service manager Taizo Mizumachi to KMUS, advising it of ongoing emergency efforts to overcome “burning” of con-rod needle roller bearings.

We were on our own. I put on a tweedy jacket and did what I could to look like a prof. I blended into the line of people entering MIT’s engineering library, located in its famous big dome. I spent the day there, reading papers from NACA (National Advisory Committee for Aeronautics) and, oddly, United Shoe Machinery Co. United Shoe seemed particularly interested in combined rolling and sliding, which strongly accelerated surface damage. I took notes.

H1R
Kawasaki introduced the H1R in 1969. New Zealander Ginger Molloy finished second in the 1970 500cc world championship riding one of the two-stroke triples. A year later, an H1R ridden by ’69 125cc world champion Dave Simmonds won the season-ending Spanish GP at Jarama.Cycle World

As I read, a picture formed. Loaded rolling contact between curved surfaces generates subsurface shear stresses. After many cycles of such stress, defects in the material may nucleate cracks that propagate through it. Such a crack typically reaches the surface of a part—a needle roller in this case, 3mm in diameter and 10.8mm long—at an angle. When it does, the sharp tip of the crack breaks off, creating a class-A surface pit. As the population of such surfacing cracks increases, two or more may join together to form a class-B pit. And now, the final stage of failure: When among these pits one forms of sufficient size, the particle of material released from the breakage of its tip is big enough to jam the roller, forcing it to slide rather than roll.

I examined their surfaces under good light and 50 times magnification: There were the pits, just as described.

I had seen that condition many times. The stopped roller slows or stops the rotation of the cage holding the rollers and the resulting sliding friction instantly heats and softens them, the piston’s inertia forces (roughly 3,000 pounds in this case) hammer them flat, and everything stops. I have examples in the shop, rollers and cage hammered into little black, jagged-edged steel pancakes. The big end of the rod is softened as well, elongating into an oval shape, heat-blackened. It is not artistic license that describes a two-stroke crank failure as “rattling to a stop.”

Returning to our shop, I removed the rollers from the about-to-fail most recently seized crank. I examined their surfaces under good light and 50 times magnification: There were the pits, just as described.

Kawasaki H1R
In the early 1990s, the Cycle World Readers Collection appeared at seven of the nationwide International Motorcycle Shows. This immaculate Kawasaki H1R, seen here with owner Tom Sherman, won the "Competition" class held at the Anaheim, California, event.Cycle World

I now believe that the rollers in the longer-lasting 1970 batch of H1R cranks were probably made of expensive vacuum-remelted bearing steel. Another Kawasaki division at the time was rebuilding military turbine engines. It surely employed engineers familiar with such new materials, which became available for military applications in 1957. Having fewer internal defects such as oxide stringers, they nucleated fewer subsurface cracks and so lasted several times longer than rollers made of conventional bearing steel. Another possible approach was to use rollers made from more temperature-tolerant tool steels such as M50.

Why were the 1971 cranks failing prematurely? Cost control is a continuing corporate activity. Maybe an eagle-eyed accountant spotted the higher price of the 1970 rollers and loyally put a stop to their use.

In any case, the key to survival on the racetrack was now to find replacement rollers made of better material. Due diligence eventually put me in touch with an outfit in New Jersey, which had in stock German-made Dürkopp needle rollers of the correct dimensions.

But were they any better than what we had? There was only one way to find out: Rebuild an H1R crankshaft with the Dürkopp rollers in its con-rod big-ends and try it. We did 26 race weekends that year and had no more unscheduled crank failures.

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