Pure racing engines usually drive their camshafts through a train of spur gears, but that solution is too noisy (because of cold backlash) and expensive (gear accuracy is costly) for mass-produced engines. At present, the popular and affordable solution is Morse chain.

My first experience with a cam chain was on a 1964 Honda Super Hawk 305cc parallel twin, and, yes, I did manage to fumble the safety clip of the master link down the chain tunnel and into the lower end. Such learning experiences are powerful and long-lasting.

When Jaguar built its sporty XK120 DOHC inline-six after WWII, the cams were driven with a 7-foot-long roller chain.

Leading up to its 1967 Formula 1 debut, the Cosworth DFV V-8 was given a proper racing cam drive of supposedly “rigid” spur gears but there was trouble. Design chief Keith Duckworth’s calculations had predicted peak cam-drive torques of 30 pound-feet, but in service the actual loads were 10 times greater and parts were breaking unpredictably.

Why such large loads? Think about it: Neither shaft rotates smoothly, yet the gears force them to rotate together. The crank is accelerated four times per revolution by a 10,000-pound shove from a cylinder firing and slows between firings. This produces violent irregular, not smooth, motion. The cams experience alternately the torques required to lift and accelerate valves against their spring forces and inertia, followed by similar but reversed forces as the valves close. As this engine revved to 10,500, there were surely torsional oscillations excited in its crankshaft, and long, slender camshafts aren’t rigid either. Somehow, all this was adding up to forces that, from time to time, broke a gear tooth.

As Ducati developed shorter-duration, higher-lift cam profiles to improve acceleration, the forces required to toss the valves back and forth became too great for the stiffness of the parts.

Duckworth had to provide some “give” in the system, but there was room in the gear drive only for the gears themselves. Therefore, he provided a circle of multiple tiny torsion bars inside a two-piece assembly, allowing just enough torsion-sprung movement to reduce the peak loads, stopping gear-tooth breakage. Modern versions include a stack of tiny clutch plates in the flexible member to provide a damping force preventing buildup of oscillations in the drive.

Torsional oscillations are serious stuff. Aftermarket V-8 cylinder blocks are now being made with huge 3-inch cam bearings (in classic V-8s, the cam installs endwise from the front in 2-inch bearings, so the bearings must be big enough to pass the lobes as well). The reason for bigger cam bearings is to allow the camshaft itself to be made torsionally stiffer as a larger and hollow tube as well as to allow the lobes to be taller. Why does it need to be stiffer? Because super-power V-8s (and the giant V-twins in NHRA Pro Stock Motorcycle drag racing) are lifting their valves 1.250 inches, at which the valve spring force is around 1,200 pounds.

Ducati did something very similar about 20 years ago in its Testastretta redesign of the eight-valve V-twin. Yes, I know, there are no valve-spring forces in Ducati's desmodromic system. But as Ducati developed shorter-duration, higher-lift cam profiles to improve acceleration, the forces required to toss the valves back and forth became too great for the stiffness of the parts. Larger-diameter hollow cams were part of the fix.

Cam-drive dynamics remain a highly active area of design in sports and racing engines.