Where Is The Camshaft Drive Located?

Crowding the cylinders closer together made for a more compact and lighter-weight engine

The camshafts in an overhead-valve engine like this Honda CBR600RR are located in the cylinder head. Two black lumps on the side seal up the little cavities used by the tooling to generate the cam bearings. A hump over the top and the broad structure indicate that the chain drive running from the crankshaft up to the two camshafts is on the end of the engine.

There is a story how the cam drive came to be on the end of the engine. In earlier examples, the cam drive was almost invariably placed in the center of the engine. With its super high-revving four-stroke Grand Prix engines of the 1960s, Honda put the primary drive—that is, engineers took the power from the crankshaft with a gear—at the middle.

They did this because they didn’t want the whole crankshaft, which was pressed together out of several parts, vibrating back and forth torsionally; they didn’t want any of those parts to slip. So putting the drive in the middle—a “still” part of the crankshaft—shortened the number of pressed joints that power had to pass through on its way to the primary gear.

Properly supporting the crankshaft meant a main bearing on either side of the center and two more on either side of it—one between each crankpin—for a total of six main bearings. By putting the cam drive on the end, they could eliminate one of those bearings, and the friction that came with it, and crowd all the cylinders that much closer together for a more compact and lighter-weight engine.

That’s what started to happen during the 1990s. The manufacturers shifted from having the camshaft drive in the center of the engine to having the drive at one end. That is one of the identifying features of the modern four-cylinder sportbike engine.