From BMW Tech
1933 BMW 3/20 type AM 4
|Automobile layout||Automobile layout|
|Internal combustion engine||788 cc (Convert/CID) Overhead valve Straight-4|
|Wheelbase||84.6 in (2,149 mm)|
|Automotive design||Alfred Böning|
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.
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 (Convert/CID). 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. 
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.. It inherited the the 3/15 DA-4's Independent suspension and added a Swing axle Independent rear suspension, using a transverse leaf spring similar to that used at the front.
Journalist and engineer Josef Ganz, who had criticized the 3/15 DA-4's suspension system in the magazine Motor-Kritik,, 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.
- Norbye, Jan P. (1984). BMW - Bavaria's Driving Machines. Skokie, IL: Publications International. ISBN 0-517-42464-9.
- "BMW's Early History". unixnerd.demon.co.uk. http://www.unixnerd.demon.co.uk/history.html. Retrieved on 2008-02-18.
- "Die Schwingachse des Kleinen" (in German). Motor-Kritik (3). February 1931.
BMW road car timeline, 1920s–1950s — next »
|Straight-4||Dixi 3/15/Dixi 3/15 DA/Dixi 3/15 DA1/||3/15 DA2/ 3/15 DA4||3/20||309|
|Sports car||DA-3 Wartburg||315/1, 319/1||328|