BMW, of course.

BMW has been making motorcycles with air cooled twin motors since 1921. While the line was discontinued in 1995 in search of more power for children who think that 100hp is called for in a single track vehicle, the design layout continues in air and oil cooled twins to this day from the BMW factory. Sure the charm and light weight have been lost but the design is as right today as it was almost a century ago.

The 900cc motor at left is in a 1975 R90/6 which is now in my 29th year of ownership. The fully faired touring rig on the right is a tad larger at 1,000cc. Both develop around 60hp, perfectly adequate for touring at 70mph all day long. The beauty of these air cooled twins is that the cylinders are way out there in the air stream, so no oil or water cooling is called for. While the later machine sports a small oil cooler it’s quite unnecessary in practice. A related benefit is that the design means that the center of gravity is very low indeed, making maneuvering at low speeds child’s play. Try horsing that high mounted Japanese ‘across the frame’ four around at parking lot speeds and you will get my drift.

Each cylinder has its own carburetor, as is clear in the image. These share the same technology present in the 1921 version and are as reliable as a hammer. Periodic valve lash check-ups and adjustments are very easy as the valve covers are simply removed (two nuts and one bolt), giving full access to the valves and followers. Rapacious and unnecessary demands for ever more power doomed these machines, which remain firm favorites with touring riders for their quietness, freedom from vibration and comfort. 300,000 miles on one of these engines is no big deal.

The last time horizontally opposed, air cooled motors were used in cars was in the original four cylinder VW Beetle and four and six cylinder Porsches, before both went to water cooling. The modern Subaru uses the design in a water cooled variant and the motors are also famously long lived.

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