BMW 3/20

BMW 3/20[1]
Overview
Manufacturer	BMW
Also called	AM-1, AM-2, AM-3, AM-4
Production	1932–1934
Assembly	Eisenach, Germany
Designer	Alfred Böning
Body and chassis
Class	City car
Body style	four seat saloon four seat cabriolet two seat convertible coupé
Layout	FR layout
Powertrain
Engine	788 cc (48.1 cu in) OHV straight-4
Transmission	4-speed manual
Dimensions
Wheelbase	2,150 mm (84.6 in)
Length	3,200 mm (126 in)
Width	1,420 mm (56 in)
Height	1,550 mm (61 in)
Kerb weight	650 kg (1,433 lb) with saloon body
Chronology
Predecessor	BMW 3/15
Successor	BMW 309

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 (48.1 cu in).^[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] The 3/20 used a backbone frame unrelated to the 3/15's Austin Seven "A" frame.^[3][4] It inherited 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][4] The standard bodies for the car were built by Daimler-Benz in Sindelfingen.^[1][4]

Journalist and engineer Josef Ganz, who had criticized the 3/15 DA-4's suspension system in the magazine Motor-Kritik,^[5] 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]

References

Citations

1. Norbye, p.30
2. Unixnerd: BMW's Early History
3. Noakes, p.24
4. Robson, p.36
5. Article ‘Die Schwingachse des Kleinen,’ Motor-Kritik magazine, issue 3, early February 1931

Sources

• Noakes, Andrew (2005). The Ultimate History of BMW. Bath, UK: Parragon Publishing. ISBN 1-4054-5316-8.
• Norbye, Jan P. (1984). BMW - Bavaria's Driving Machines. Skokie, IL: Publications International. ISBN 0-517-42464-9.
• Robson, Graham (2008-11-07). "The First Cars—Dixi, BMW, and Advanced Engineering". Inside the BMW Factories: Building the Ultimate Driving Machine. Minneapolis, MN US: MBI Publishing. p 36 The development of the 3/20. ISBN 978-0-7603-3463-8. Retrieved 2013-02-15.
• "BMW's Early History". unixnerd.demon.co.uk. Archived from the original on 23 February 2008. Retrieved 2008-02-18.
• Ganz, Josef (February 1931). "Die Schwingachse des Kleinen". Motor-Kritik (in German) (3).