BMW 3/20

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BMW 3/20
BMW AM 4 1933 red vl closed top.jpg
1933 BMW 3/20 type AM 4
Production start1932[1]
Production end1934[1]
AssemblyEisenach, Germany
PredecessorBMW 3/15
SuccessorBMW 309
LayoutFR layout
Engine(s)788 cc (Template:Convert/CID) OHV straight-4[1]
Wheelbase84.6 in (2,149 mm)
DesignerAlfred Böning
ManualsService Manual

The BMW 3/20 PS was the first BMW automobile designed entirely by BMW. It was manufactured from 1932 to 1934, replacing the 3/15 model that was initially an Austin 7 manufactured under licence from the Austin Motor Company.

BMW 3/20 AM 4 engine

The engine used in the 3/20 was based on the Austin Seven engine used in the 3/15, but its crankshaft ran in plain bearings instead of roller bearings and had an 80 mm (3.1 in) stroke, generating a displacement of 788 cc (Template:Convert/CID).[1] The new engine design also had a water pump and an overhead valve cylinder head. These design changes caused the engine to generate 20 hp, but did not change the taxable horsepower rating of 3 PS, thus giving the model designation 3/20. [2]

The 3/20 was larger than the 3/15, with an 84.6 in (2,149 mm) wheelbase and a body 3 in (76 mm) lower than the 3/15.[2]. It inherited the the 3/15 DA-4's independent front suspension and added a swing axle independent rear suspension, using a transverse leaf spring similar to that used at the front.[1]

Journalist and engineer Josef Ganz, who had criticized the 3/15 DA-4's suspension system in the magazine Motor-Kritik,[3], was contracted in July 1931 as a consultant in the design of the 3/20 AM-1.

Four versions of the 3/20 were built: AM 1, AM 2, AM 3 and AM 4, where AM denoted Automobil München.[1]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Norbye, p.30
  2. 2.0 2.1 Unixnerd: BMW's Early History
  3. Article ‘Die Schwingachse des Kleinen,’ Motor-Kritik magazine, issue 3, early February 1931