|BMW Type 253 in the BMW Collection (Munich)|
A little history
In the post war effort to develop a motorcycle that could challenge the brits, there evolved at BMW an enigmatic machine colloquially known as the RS54.
The machine was the culmination of design efforts beginning well before the war when Schleicher helped develop the Koenigswelle, or "King Shaft" supercharged bikes that had positioned Schorsch Meier atop the leader board at the 1939 Isle of Mann Senior TT race.
As the platform developed, the double overhead cam design was refined. After several iterations, in 1953, BMW began campaigning and showing early prototypes of a motorcycle that would go on to become a small production run of machines for a select few racers.
The bikes produced numbered approximately 25, and all were long stroke versions, equipped originally with 4 speed gear boxes. Six of the original machines were "seitenwagen" or side-cars.
While not overly successful in solo form, the engine platform was utilized in the ensuing decades to harness no fewer than 18 side-car world championships in 20 years. This was an amazing feat, unlikely to ever be duplicated.
Of course development wasn't static. Long stroke engines gave way to short stroke version. The original 30 mm Amal Fischer carburetors were exchanged for 32 or 35 mm Dell'Ortos. (Some works bikes were fuel injected.) A five speed gear box was available.
In later years, massive carburetors fed the boxer motors that by then wound greater than 10K rpm. Double plugged heads were commonplace. The kneeler, with its tremendously low center of gravity, became the preferred configuration.
A victim of it's own success in the side-car arena, most original long stroke bikes were dismantled, and frames discarded or modified for use in side car racing. For this reason, there exists today no complete bike that the author is aware of, with the original frame and long stroke motor.
|Ex Auerbacher/Hahn kneeler.|
The bike referred to is the RS54 or "Rennsport". Of course the term Rennsport is rather generic German word referring to any matter of racing car or motorcycle. However if you ask any BMW motorcycle aficionado about the "BMW Rennsport" they will understand that you are referring to the DOHC boxer race bike developed in the 1950's.
It is unclear how and when the term RS54 came into use. The origins are simple to deduce. RS of course referring to RennSport and 54 being the year of production (though the bike was shown one year earlier in slightly different trim than was used on productions bikes.)
Interestingly, there is no reference to RS54 in any of the BMW documentation of the day. Internally, the bike was known as the Type 253 Rennmaschine.
Even this nomenclature continues to be wrongly used today. As noted above, there were approximately 25 factory produced long stroke bikes, sold to customers or dealerships, however there was an unknown number of machines developed at the Works for use by the factory team, including Walter Zeller.
These bikes were seen with various "works" parts including a larger magnesium front brake, fuel injection, fairing, Drehmoment schwinge (special rear swingarm and drive shaft). These bikes have been referred to as Type 256, however this too is an incorrect term. As the type 253 platform developed, or changes were made, the new designation had a letter added, i.e. Type 253f.
Unfortunately, the record keeping with respect to develop of these bikes is either woefully inadequate, or a tightly kept secret. Be that is at may, it is unlikely that my essay here will change the terms we use to describe these fantastic machines!
|Daniela Weingartner at Goodwood 2014. This machine is part of the BMW collection in Munich. Photo BMW.|