1954 BMW Rennsport RS54
Chassis no. 549012
Engine no. 549012
While BMW had captured the world's attention before WW2 by repeatedly capturing the World Land Speed Record with its supercharged streamliners, winning the European Championship in 1938 and the Isle of Man TT in '39, all German factories (BMW, NSU, DKW, etc) were barred from international competition immediately post-war. Yet each carried on developing their 'old' supercharged designs for domestic championship honors, while retooling for renewed civilian production. When Germany was again admitted to worldwide FIM-sanctioned events, each factory 'set to' with renewed vigor; with the burgeoning economy of their 'economic miracle' and exploding sales of two-wheelers, the BMW factory invested in upgrading their prewar RS255, built for supercharging, into modern, normally-aspirated GP racers.
Their new designs retained much of the old 'Kompressor' engine design on paper, with twin gear-driven camshafts compactly hidden in the cylinder heads, but the engine was nearly all-new, while the greatest change came to the now cutting-edge chassis. The introduction of a full loop, all-welded lightweight frame with proper swingarm suspension and hydraulic damped shocks, plus the latest ultra-rigid front fork design licensed from Englishman Ernie Earles, brought the BMW back in the game.
What wasn't expected was the announcement in 1953 that BMW would offer well-heeled professionals a genuine production racer, closely modeled on the Works' machines. The RS ('Rennsport') 54 could be found in black and white (and blue!) in the factory catalog, although perhaps only 24 were ultimately built by BMW. What the factory offered was a 130kg (286lb) DOHC dedicated racing machine producing a nominal 45hp, which on paper compared well with its competition, the Norton 'Manx' with all-welded Featherbed frame and DOHC engine, which produced perhaps 50hp, but was 10kg (22lbs) heavier. While the BMW had theoretical advantages as a production racer over rival Norton, with a lighter weight and a lower center of gravity, the BMW never handled quite as well, but then again, it never leaked oil (as from Norton's open cambox) over the rear tire!
The RS54 was introduced two years before BMW roadsters converted to swingarm suspension front and rear (in 1955), using Earles forks and a far less 'Featherbedish' frame than the RS54, with extended loops holding upright hydraulic shocks. The new roadster line never looked as rakish and fast (nor were they as anywhere near as light, at 195kg/430lbs), and the RS54 was the bike BMW enthusiasts Really wanted, but with such small and selective production, ownership was out of the question for all but a lucky few professionals.
The RS54 initially had bore and stroke dimensions of 66 x 72 mm, giving 492cc, although with later development, the engine became 'square' at 68 x 68 mm, while the 'Works' racing machines used 70 x 64 mm bore and stroke eventually. The camshafts were driven by a shaft-and-bevel system, running on needle roller bearings throughout. To keep the cylinder head short, the exhaust cam (driven from the engine) was geared direct to the inlet cam, and drove the valves by short, flat rockers. Valves were set at a wide 82 degree angle in the semi-spherical heads, using duplex coil springs held by stepped aluminum keepers.
Amal-Fischer TT carburetors (made under license since the 1930s) of 30mm were mounted at 15 degrees downdraught. The crankshaft ran in three main bearings inside a one-piece cast crankcase, at the front of which gears drove the oil pump and magneto, which sat atop the engine. The connecting rods used a flat section, as tests showed cracking with a more typical 'I' section rod. Forged Mahle pistons of only 8:1 compression ratio ran inside cast aluminum cylinders, with either a shrunk-in iron liner, or chrome-plated plain barrel, with six stud crankcase fixing. The typical BMW engine-speed flywheel clutch drove a four-speed gearbox, and the final driveshaft was housed inside the right-hand swingarm tube, although unlike the later production models, the swingarm did not hold oil.
To stop the machine, an aluminum 200mm twin-leading shoe full-width brake graced the Earles forks, while a single leading shoe drum fixed the rear swingarm. A hydraulic drum brake, as fitted to the later Works racers and sidecar machines, sometimes found their way to the RS54 as well. Other developments of the RS54 included a shorter-stroke engine of 68x68mm (the Works engines used 70x64mm at the end, and these dimensions migrated to many RS54s in later competitive life), a five-speed gearbox, higher compression pistons, larger Dell'Orto SS1 carbs, etc.
This BMW RS54, engine #549012, corresponds with an early-type, long-stroke '253-1' Rennsport. The machine is currently fitted with a 5 speed gearbox, a Bosch magneto (stamped H241-72), Smiths 10k rpm tachometer, aluminum fuel tank with Enots 'Monza' filler, crankshaft-driven 90degree tachometer drive, and early type frame with a single strengthening cross-tube below the swing-arm, Dell'Orto SS1 carburetors, and correct twin-leading shoe RS54 front brake.