~ Auto Buzz ~: Will BMW Build a W-3 Engine? These drawings prove that BMW is considering this pushrod W-3, which could find a home in a new cruiser.

BMW is seeking patents on two concepts for building air-cooled pushrod W-3 engines. Historically, such designs have come into being when a maker (such as Glenn Curtiss in 1910, or the late Jim Feuling in 2000) wants more power than an existing V-twin can deliver. The attraction of the W-3 is that it can notionally fit into a chassis originally designed for the twin. When Feuling prototyped his concept, he left the original pair of cylinders where they were and added the third cylinder ahead of them. To make room, he moved the steering head forward. BMW’s patent drawings envision two architectures:

A transverse crankshaft with three crankpins and four main bearings. Seen from the side, the three air-cooled cylinders would have the W configuration, but seen from the front, the cylinders would be offset from each other by a distance equal to the crankpin spacing. This offers a cooling advantage as each cylinder has access to fresh cooling air.

2) A transverse crankshaft with two crankpins and three main bearings. The left crankpin would carry the single connecting rod of the left cylinder but the longer right crankpin would carry two conrods side by side (as they are in the fabled Vincent V-twins).

To meet the modern rider’s expectation of smoothness, both engines would carry a gear-driven balance shaft ahead of the crank.

Although all of BMW’s recent motorcycle engines are either liquid-cooled or have liquid-assisted cooling of their exhaust valve areas, the company has long experience with air-cooling. We naturally remember BMW’s 1-2 victory in the 1939 Senior Isle of Man TT (photo above), using an air-cooled and supercharged flat-twin, but the company also produced 61,000 of its very sophisticated air-cooled 801 radial piston engines for the wartime FW-190 fighter.

When Fueling built his W-3 (for which he claimed 150 hp), only the conrod of the center cylinder attached to the crankpin. The pistons of the outer cylinders attached to link rods that attached to pivot lugs on the outside of the master rod’s big end. Glenn Curtiss did the same. Thus, all three cylinders were in the same plane, which compromises cooling by placing the aft cylinders in the front cylinder’s wind shadow. It is surely to overcome this problem that BMW’s scheme above (1) offsets the three cylinders.

A very successful W engine from long ago was the liquid-cooled W-12 Napier Lion, which used the master-and-links conrod system. Because the master-and-links system introduced difficult vibration problems, later V-engines such as the Rolls-Royce Merlin and the American Allison V-12 were given knife-and-fork rod systems of the kind that Harley’s Big Twin has to this day.

Another historical example of interest is the 24-hp W-3 or “fan engine” built by Anzani and used by Louis Bleriot on his pioneering 1910 flight across the English Channel. Anzani’s use of this configuration is attributed to previous experience in building motorcycle engines. A year later, Anzani switched to a better-balanced 120-degree radial configuration for aircraft use. Something common to both of BMW’s concepts is their robust plain-bearing lower ends, which could be made to last practically forever. Will BMW actually build some kind of mighty air-cooled pushrod cruiser? Your guess is as good as mine, but who can ignore the market Ducati discovered with their Diavel? Every company continuously conceives, patents, and even prototypes a stream of novelties, of which few actually reach production. The patent system affords us a small window through which we can watch the process at work.