BOXING CLEVER
BMW’s new R18 represents the pinnacle of their opposed twin layout, but it’s an engine that’s been 100 years in the making
The 1802cc air-cooled unit inside the new R18 is the largest and torquiest boxer BMW have ever built. It sets a whole new standard in modern, air-cooled engine design but the basic layout stretches back exactly 100 years.
Early beginnings
BMW started life as Bayerische Flugzeugwerke (Bavarian Planeworks) in 1916 and specialised in aircraft engines. After Germany were defeated in World War I, their military were disbanded and the Treaty of Versailles was signed to prevent the country from rebuilding their armed forces. Bayerische Flugzeugwerke were forced to change direction and in 1919, they built the M2B15, 500cc side-valve flat twin engine with the intention of it being used as a stationary engine to power machinery. Local motorcycle maker Victoria AG bought the M2B15 and used it in their KR1. Fancying a piece of the action, BFW built their own bike and called it the Helios. Less than a year later BFW merged with a local firm called Bayerische Motoren Werke (Bavarian Motor Works) and BMW AG was formed.
BMW inherited the BFW Helios and set about trying to improve on it. The Helios was a copy of a 1914 Douglas, so the engine was mounted longitudinally, enabling a simple final drive. The downside was that the rear cylinder suffered from terrible cooling issues, such that BMW’s then head of design proposed the best way they could improve a Helios was to throw it in a canal. After a bit of thought he proposed a short-term solution: spinning the engine 90-degrees so that each cylinder sat in the wind. Then to get the power down, he suggested a shaft drive, with a 90-degree bevel at the rear wheel. The test was a success and BMW put the bike into production in 1923 as the R32.
Solid foundations
The R32 was a hit and laid the foundations for future BMWs. When it was first released, is was revolutionary in ways that now seem quite banal. It ran a wet sump for instance, so oil could be dripped onto the crank bearings, rather than the total loss systems common at the time. BMW’s next big step was with the R37, which had overhead valves, followed by the R5, which brought with it two camshafts and the first foreign win of the Senior TT in 1939. The design of the R5 set up BMW’s boxers for the next 30 years and went on to become the inspiration for the new R18.
Fast foward to the 60s and 70s and with the notable exception of the then aging R69S, BMW’s twins became seen as old-fashioned and expensive tourers. Worse, their shortcomings were being exposed by a new breed of Japanese superbikes that were proving increasingly popular in the US market. In response, in late 1966, BMW set on a course for a radical overhaul: along with the decision to can the small capacity singles and relocate to Berlin, the marque began developing an all-new family of bikes. Former Porsche designer Hans-Gunther von der Marwitz headed up the project. He wanted to follow the tradition of former BMW racers Rudolf Schleicher (who created the R5) and Alexander von Falkenhausen by using race technology to create a new BMW that was not only fast but also reliable. What he came up with, while still being a classic air-cooled boxer with shaft drive, was also one with a host of tech innovations, fundamentally lighter and better performing than before yet maintained the BMW values of quality, durability and comfort.
A truly modular engine
Development of the new engine, designated the Type 247 but commonly known as the ‘airhead’, was overseen by von Falkenhausen and Ferdinand Jardin with the result considered the first true ‘modular’ BMW engine. Three new bikes would use the new engine and form the /5 range with the main difference being the bore size being changed according to capacity. Equally important was a desire to make the air-cooled boxer look more modern. New, taller, one-piece aluminium crankcases rose right up to the fuel tank and now contained an electric starter motor. There was a new one-piece forged crankshaft running in plain bearings. While the pushrods were now placed under the cylinders to leave the top of the barrels free from