BMW M78
Template:Infobox automobile engine
The BMW M78 is a petrol overhead valve straight-six engine which was produced from 1933 to 1950.[1] 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.[2]
The M78 was launched in the 1933 BMW 303.[3] 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.[4]Template:Refpage[5]
Design
The M78 was designed by Rudolf Schleicher[3]Template:Refpage[6] as a medium power straight-6 engine.[7] Initial versions of the M78 had the same bore and stroke as the BMW 3/20's four-cylinder engine.[8] 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 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 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.[7]
Models
| Model | Displacement | Power | Year |
|---|---|---|---|
| 303 version | Script error: No such module "convert". | Script error: No such module "convert". | 1933-1934 |
| 315 version | Script error: No such module "convert". | Script error: No such module "convert". | 1934-1937 |
| 315/1 version | Script error: No such module "convert". | ||
| 319 version | Script error: No such module "convert". | Script error: No such module "convert". | 1935-1937 |
| 319/1 version | Script error: No such module "convert". | ||
| 326 version | Script error: No such module "convert". | Script error: No such module "convert". | 1936-1950 |
| 320 version | Script error: No such module "convert". | 1937-1938 | |
| 327 version | Script error: No such module "convert". | 1937-1953 | |
| [9] | |||
303 version
This first version of the M78 had a bore of Script error: No such module "convert"., a stroke of Script error: No such module "convert". and a compression ratio of 5.6:1.[4]Template:Refpage It produces Script error: No such module "convert". and Script error: No such module "convert"..[10][1]
Applications:
- 1933-1934 303
315 version
A development of the 303 version, where the bore was increased from Script error: No such module "convert". and the stroke was increased from Script error: No such module "convert"..[4]Template:Refpage The compression ratio remained at 5.6:1.[4]Template:Refpage[11] This engine produces Script error: No such module "convert". at 4000 rpm.[11]
Applications:
- 1934-1937 315
315/1 version
An upgraded version of the 315 engine with the compression ratio increased to 6.8:1[4]Template:Refpage[12] and using three Solex carburetors.[4]Template:Refpage[12] This version produces Script error: No such module "convert". at 4000 rpm.[12]
Applications
- 1934-1937 315/1
319 version
The 315 engine was enlarged to Script error: No such module "convert". for the 319.[13] This was a result of increasing the bore to Script error: No such module "convert". and the stroke to Script error: No such module "convert".. This engine produces Script error: No such module "convert". at 3750 rpm.[4]Template:Refpage
Applications:
319/1 version
The 315/1 engine was enlarged to Script error: No such module "convert". for the 319/1.[13] This was a result of increasing the bore to Script error: No such module "convert". and the stroke to Script error: No such module "convert".. This engine produces Script error: No such module "convert". at 4000 rpm.[4]Template:Refpage
Applications:
- 1935-1937 319/1
326 version
The 319 engine was enlarged to Script error: No such module "convert". for the 326 by increasing the bore by one millimetre to Script error: No such module "convert".. Twin Script error: No such module "convert". Solex carburetors were used. The compression ratio was raised to 6.0:1.[4]Template:Refpage This engine produces Script error: No such module "convert". at 3750 rpm.[4]Template:Refpage[14]
Applications:
320 version
The 326 engine was detuned (by using a single carburetor) for the 320 and 321. This engine produces Script error: No such module "convert". at 3750 rpm.[15]
Applications:
327 version
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 Script error: No such module "convert". at 4500 rpm.[4]Template:Refpage The engine retains its 66 by 96 mm bore and stroke, resulting in a displacement of Template:Cvt. The engine has a BMEP of Template:Cvt at 3750/min, equivalent to a max torque of Template:Cvt at 3750/min.[7]
Applications:
See also
References
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