Digitally reporting how we feel about things has become the winning play, so perhaps I should begin by saying that I’m really into finger followers but am wrestling with a previous emotional attachment to inverted-bucket-and-shim tappets. I must get counseling before I’m mentally torn apart by this.

In four-stroke engines the intake and exhaust valves open and close once in a complete cycle of two crank revolutions. They are opened and closed by a combination of cams (which are smooth bumps projecting from an otherwise circular shape) and springs (exception: Ducatis with desmo valves, which are opened by one cam and closed by another—no springs).

Each valve resembles a tiny manhole cover on a stick; the manhole cover is the valve head which, when closed, seals either an intake or exhaust port in the cylinder head, which in turn covers the top of a cylinder. Each little “manhole cover” (often about the size of a quarter) is guided to its seat by its “stick,” called the valve stem. The valve stem slides back and forth in a valve guide that is pressed into the cylinder head. Each valve is held closed against its seat by coil springs, used singly or in nested pairs.

A cam lobe cannot simply press against the end of the valve stem to open the valve; the stem, being quite small in diameter, would soon gouge up the smooth-surfaced cam lobe. So we need to put something broader and smoother between the valve stem and the cam lobe. For many years that has been the classic inverted-bucket tappet, which is a short little quarter-sized steel cup that fits down over the valve stem and valve spring(s), guided by closely fitting into a bore in the cylinder head.

As the cam lobe, rotating at half crankshaft speed, swings around, it begins to push this bucket tappet downward, opening the valve under it. The wide, smooth, and hard closed end of this tappet forms an excellent friction surface against which the lobe operates. Random rotation of the bucket tappet serves to equalize wear in all directions, making it last many tens of thousands of miles.

Honda used such bucket tappets on all of its classic 1960s four-stroke roadracing engines, including the 20,500-rpm RC149 five-cylinder 125 of 1967.

Yet a bucket tappet contains extra weight—the length necessary to guide it in its bore, and its extra width, projecting beyond the narrow cam lobe on both sides. When it becomes necessary to make valve-train parts as light as possible to allow operation at high engine rpm and/or high valve acceleration rates, the finger-type cam follower is the best choice. It is a lever, pivoted at one end with the other end bearing against the end of the valve stem, and it is in no part wider than the cam lobe. Facing the cam lobe is a smoothly ground curved pad, given great surface hardness to resist wear. As the cam lobe presses against this pad, the moving end of the lever pushes against the valve stem, opening the valve. As always, continuous lubrication is the key to durability.

When Kawasaki recently switched its ZX-10R literbike from inverted bucket tappets to finger followers, the project leader on that model, Seiji Azuma, had this to say about the change:

"To gain low-end torque you want a shorter duration (shorter total valve-open time), however for top-end power you need a higher lift [maximum opening of the valve], which requires a very aggressive profile on the cam [i.e., a high rate of valve acceleration as it opens], which you can achieve using finger followers but not [with] a bucket-and-shim system."

Azuma went on to say that while bucket tappets have a simple round shape that is easily made on a lathe, finger followers have a complex shape that must either be forged or machined from solid, both of which add costs. This is why bucket tappets have continued to be used over many years and in so many motorcycle models—even though their greater weight limits valve-train performance somewhat.

Kawasaki 2019 ZX-10R engine
Kawasaki’s 2019 ZX-10R uses finger followers to achieve shorter duration and higher valve lift while reducing weight.Kawasaki

While looking into the design of early Honda auto racing engines, I found a photo of a cutaway Formula 2 engine displayed in its Motegi Collection Hall. This engine was last raced in 1968 but its design had begun at least four years earlier. When I enlarged the photo I saw this engine from 51 years ago had finger followers machined from solid steel.

Thinking there must be more to this story, I searched for more information on this F2 engine. Two of Honda’s greatest engineers, Yoshio Nakamura and Tadashi Kume, had been principals in the early development of Honda formula cars. In 1965 driver Jack Brabham had explained to them the critical importance of giving the engine broad torque instead of the peaky power its original design delivered. In order to achieve that, Nakamura and Kume had to do what Seiji Azuma described (above) a half-century later: shorten the valve timing and increase valve lift. Because that required reaching a higher lift in less time, valve acceleration had to be very high. To achieve that acceleration without valve float (failure to follow the cam lobe) it became crucial to reduce valve train weight as much as possible. Finger followers were the logical choice.

When Honda, in replying to Yamaha’s late-1970s marketplace challenge, designed the liquid-cooled V-4 VF750, they wanted it to deliver the wide powerband Brabham had described years before. Therefore it was given finger followers.

Today finger followers have made a comeback wherever the best combination of acceleration and top power is required. At present that includes Suzuki’s GSX-R1000, Yamaha’s YZF-R1, the BMW S 1000 RR, and Kawasaki’s ZX-10R.