The BMW M78 is a petrol overhead valve straight-six engine which was produced from 1933 to 1950. It is the first straight-6 automobile engine produced by BMW, an engine layout which has been a key feature of the brand for many years since.
31-570: The M78 was launched in the 1933 BMW 303 . In 1936, the higher performance BMW M328 straight-six engine began to be produced alongside the M78. In 1952, the BMW M337 engine was introduced as the replacement to the M78. Compared with the M78, the M337 has a revised cylinder head, a new inlet manifold and a reinforced crankshaft with bigger, more modern bearings. The M78 was designed by Rudolf Schleicher as
62-441: A compression ratio of 5.6:1. It produces 22 kW (30 PS) and 68 N⋅m (50 lb⋅ft). Applications: A development of the 303 version, where the bore was increased from 56 to 58 mm (2.20 to 2.28 in) and the stroke was increased from 80 to 94 mm (3.15 to 3.70 in). The compression ratio remained at 5.6:1. This engine produces 25 kW (34 PS) at 4000 rpm. Applications: An upgraded version of
93-404: A drum brake ; all four were operated through the pedal using rods and levers, while the rear brakes were also operated by cables from the handbrake lever . The 303 was the first BMW car to use a straight-6 engine. The M78 1182 cc six-cylinder engine was developed from the four-cylinder engine used in the 3/20. The engine had the same bore and stroke as the four, but the bore spacing
124-399: A displacement of 1,971 cc (120.3 cu in). In the 326 application, it was fed by twin 26 mm Solex carburetors to produce a claimed maximum output of 50 PS (37 kW) at 3750 rpm . The top speed is 115 km/h (71 mph). The four-speed gear box was supported by freewheeling on the bottom ratios and synchromesh on the top two. The 326 was introduced at
155-408: A displacement of 1,971 cm (120.3 in). The engine has a BMEP of 6.7 kp/cm (0.66 MPa; 95.30 lbf/in) at 3750/min, equivalent to a max torque of 104 N⋅m (10.6 kp⋅m; 76.7 lb⋅ft) at 3750/min. Applications: BMW 303 The BMW 303 was a small family saloon produced by BMW in 1933 and 1934. It was the first BMW motor car with a six-cylinder engine and
186-452: A medium power straight-6 engine. Initial versions of the M78 had the same bore and stroke as the BMW 3/20 's four-cylinder engine. The M78 has two main cast pieces, the iron cylinder block, and the reverse-flow cylinder head , also made from iron. The oilpan, and the cylinder head cover are made from pressed steel. In addition to that, the M78 has a pressed-steel cover for the chain that drives
217-454: A transverse mounted leaf spring mounted above the wheel centre line. The hubs were located with the spring mounts at the top and control arms at the bottom. The rear suspension used a live axle on semi-elliptic leaf springs, a conventional system neither as advanced nor as troublesome as the 3/20's swing axles . The 303 was the first German car in its size and price class to have automatic "one-shot" chassis lubrication. Each wheel had
248-493: A two-seat sports cabriolet for the 303. At the time it was being made, the 303 was the least expensive six-cylinder car in Germany. However, it was considered underpowered, with a top speed of 90 km/h (56 mph). The combination of soft spring rates at the front and hard spring rates at the rear caused understeer , body roll , and a generally unsettling pitching movement. 2300 BMW 303s were produced up to 1934, when
279-421: The BMW 329 , a development of the 319 with styling based on the newer, larger BMW 326 , that briefly replaced the 319 in 1937. The 303 platform was also used for the BMW 315/1 and BMW 319/1 . These were high-performance versions of the 315 and 319 respectively, with tuned engines and lightweight roadster bodywork. The 315/1 and 319/1 were replaced by the BMW 328 in 1936. Upon its introduction in 1933,
310-658: The Berlin Motor Show in February 1936, the 326 was offered for sale from May of that year. The 326 was a success. By the time production was suspended in 1941, the Eisenach plant had produced 15,949 of them. In 1945, Eisenach was occupied by US forces. However, the wartime allies had already agreed that Thuringia would fall within the Soviet occupation zone . The plant that BMW had originally acquired in 1929
341-484: The torsion bar rear suspension, inspired by the dead axle suspension of the Citroën Traction Avant , and the hydraulic braking system , the first to be used on a BMW car. Styled by Peter Szymanowski, the 326 was offered as a four-door sedan and as a two- or four-door cabriolet. The 326 sedan was the first BMW available with four doors. The BMW 320 , BMW 321 , BMW 327 , and BMW 335 were based on
SECTION 10
#1732772566955372-556: The 303 was replaced by the 315. The BMW 309 was a development of the 303. A replacement for the 3/20, the 309 was a 303 with a four-cylinder engine developed from the M78 six-cylinder engine used in the 303. The 309's engine had the bore increased from 56 mm (2.2 in) to 58 mm (2.3 in) which, with a stroke of 80 mm (3.1 in), gave a capacity of 845 cc (51.6 cu in) and maximum power of 16.5 kW (22 PS; 22 hp) at 4000 rpm. In addition to
403-509: The 303 was the largest car BMW had made. The wheelbase of the 303 was 2,400 mm (94.5 in), an increase of 300 mm (11.8 in) over the 3/20 . The track, 1,150 mm (45.3 in) at the front and 1,220 mm (48.0 in) at the rear, was also wider than the 3/20's 1,100 mm (43.3 in) front and rear. Unlike the 3/20's backbone chassis , the 303 had a ladder frame made from tubular side members and box-section cross members. The independent front suspension used
434-470: The 315 engine with the compression ratio increased to 6.8:1 and using three Solex carburetors . This version produces 29 kW (40 PS) at 4000 rpm. Applications The 315 engine was enlarged to 1,911 cc (116.6 cu in) for the 319. This was a result of increasing the bore to 65 mm (2.56 in) and the stroke to 96 mm (3.78 in). This engine produces 33 kW (45 PS) at 3750 rpm. Applications: The 315/1 engine
465-507: The 319 was 850 kg (1,874 lb), and the fuel capacity was 40 L (11 US gal; 9 imp gal). Upon the introduction of the BMW 326 in 1936, the 315 and 319 were no longer BMW's largest cars. The 315 and 319 were discontinued in 1937. A total of 9,765 BMW 315s were built, including two-door saloon cars, touring cars, convertibles, sport convertibles, and 315/1 roadsters. A total of 6,646 BMW 319s of all types were built by
496-426: The 319's engine with the performance modification of the 315/1's engine resulted in 41 kW (55.0 hp) at 4000 rpm in the 319/1 roadster. Production of the 315/1 and 319/1 roadsters ended in 1936, with 242 of the 315/1 roadsters and 102 of the 319/1s built. The 315/1 and 319/1 were replaced by the BMW 328 , which was based on an all-new tubular steel ladder frame, but used the steering gear and suspension of
527-473: The 319/1. BMW 326 The BMW 326 is a medium-sized sedan produced by BMW between 1936 and 1941, and again briefly, under Soviet control, after 1945. The 326 was BMW's first four-door sedan. It had an innovative design and sold well despite its relatively high price. It also had an unusually involved afterlife. Designed by Fritz Fiedler , the 326 featured a box-section frame that could readily be adapted for derivative models. Also innovative were
558-413: The 326. The streamlined form of the body contrasted with previous relatively upright BMWs: drag was presumably reduced further by including a fixed cover over the spare wheel at the back. The 1971 cc straight 6 engine was a version of the 319 ’s power plant, with the bore increased from 65 mm (2.6 in) to 66 mm (2.6 in), and an unchanged stroke of 96 mm (3.8 in) giving
589-560: The 326. Detailed plans of the sedan and coupé derivative models were also rescued by the British. Family connections, involving the founder of the Bristol Aeroplane Company and a Frazer-Nash director who had imported to England and adapted BMW designs in the 1930s, led to Bristol. A succession of Bristols cars introduced between 1947 and 1953 were unapologetic developments of the respected BMW design. Ten years after
620-497: The BMW name. It was, perhaps, a tribute to the 326's perceived excellence, together with the skills of the workers who had struggled to revive it, that the Eisenach plant was permitted to produce the BMW design till approximately 1955, long after the Auto Union assembly facilities at nearby Zwickau had been dismantled and removed to Russia as part of the war reparations package. The Russians were not alone in being impressed by
651-428: The alternator. The spark plugs are installed almost horizontally, below the intake manifold. BMW installed two horizontal draught Solex 26 mm carburettors next to the engine block and flange-mounted them to the intake manifold that sits atop them, i.e. the carburettors "hang down" from the intake manifold. This first version of the M78 had a bore of 56 mm (2.20 in), a stroke of 80 mm (3.15 in) and
SECTION 20
#1732772566955682-418: The body styles offered with the 303, the 309 was also available as a tourer . With the same body as the 303, the 309 offered the same amount of room at a lower cost and a lower tax rating based on its smaller engine. The 309 was manufactured from 1934 to 1936, with a total of 6,000 made. The 315 replaced the 303 in 1934. The 315 differed from the 303 mainly with its larger engine, with increases in both
713-520: The bore, to 58 mm (2.3 in) from 56 mm (2.2 in), and the stroke, to 94 mm (3.7 in) from 80 mm (3.1 in). The 319 were introduced in 1935. Produced alongside the 315, the 319 differed from it mainly by its new, larger engine with a bore of 65 mm (2.6 in), and a stroke of 96 mm (3.8 in), resulting in a displacement of 1,911 cc (116.6 cu in). This resulted in an increase in power to 34 kW (45.6 hp) at 3750 rpm. The kerb weight of
744-425: The end of production in 1937. The 329 replaced the 319 in early 1937. The 329 was basically a 319 with the front bodywork and fenders from the BMW 326 . The 329 was available only as a convertible, with either two or four doors. The 329 was replaced by the 326-based BMW 320 later in 1937. The BMW 315/1 was a sports car based on the 315 saloon. It used the same chassis as the 315 saloon and had an engine of
775-406: The first BMW motor car with the "kidney grille" associated with the brand . The platform developed for the 303 was used for several other BMW cars, including the BMW 309 , a four-cylinder version of the 303, the BMW 315 , a 1.5-litre version of the 303 which replaced it in 1934 and was built until 1937, the BMW 319 , a 1.9-litre version of the 303 produced alongside the 315 from 1935 to 1937, and
806-407: The in-block camshaft. Both the crankshaft, and the camshaft have four bearings. The camshaft also drives the shaft for the oil pump and the ignition distributor. The engine has overhead valves that are actuated through pushrods and rocker arms. The water pump is flange-mounted to the cylinder head, and powered by a belt that is driven by a pulley that is flanged to the crankshaft. The belt also powers
837-412: The same displacement. However, with compression ratio increased to 6.8:1 from 5.6:1 in the saloon, and with the use of three Solex carburetors, power increased to 30 kW (41 PS; 40 hp) at 4300 rpm, while the roadster bodywork reduced kerb weight to 750 kg (1,653 lb). The BMW 319/1 was a 1.9-litre version of the 315/1 introduced alongside the 319 in 1935. The dimensions of
868-469: Was enlarged to 1.9 L (1,911 cc) for the 319/1. This was a result of increasing the bore to 65 mm (2.56 in) and the stroke to 96 mm (3.78 in). This engine produces 40 kW (55 PS) at 4000 rpm. Applications: The 319 engine was enlarged to 2.0 L (1,971 cc) for the 326 by increasing the bore by one millimetre to 66 mm (2.6 in). Twin 26 mm (1.0 in) Solex carburetors were used. The compression ratio
899-593: Was increased to allow for further increases in bore and to provide for crankshaft bearings between the ends of the crankshaft. The crankshaft ran in four plain bearings . The 303 was the first BMW to use the 'kidney grill', which has since become a defining feature of the company's models. Two-door saloon and cabriolet bodies were manufactured, at first by Daimler-Benz 's coachworks in Sindelfingen , and later by Ambi-Budd in Berlin. Ambi-Budd would also offer
930-409: Was not fully destroyed, and it was possible for returning survivors to assemble sixteen postwar 326s. A modernised version, badged initially as the BMW 340 , emerged around 1948. Despite the nomenclature, it was clear that BMW’s Eisenach plant was no longer under the control of BMW: later BMW 340s, still based on the prewar 326, were badged as EMW 340s following a protracted dispute concerning title to
961-496: Was raised to 6.0:1. This engine produces 37 kW (50 PS) at 3750 rpm. Applications: The 326 engine was detuned (by using a single carburetor) for the 320 and 321. This engine produces 33 kW (45 PS) at 3750 rpm. Applications: The 327 used a version of the 326 engine with a new cylinder head, yielding a 6.3:1 compression ratio and a slight power increase to 40 kW (55 PS) at 4500 rpm. The engine retains its 66 by 96 mm bore and stroke, resulting in