| BMW 3/20 | |
| Manufacturer: | BMW |
| Aka: | AM-1, AM-2, AM-3, AM-4 |
| Production: | 1932–1934 |
| Assembly: | Germany: Eisenach |
| Predecessor: | BMW 3/15 |
| Successor: | BMW 309 |
| Class: | City car |
| Body Style: | four seat saloon four seat cabriolet two seat convertible coupé |
| Layout: | FR layout |
| Engine: | 7881NaN1 OHV straight-4 |
| Transmission: | 4-speed manual |
| Wheelbase: | 21501NaN1 |
| Length: | 32000NaN0 |
| Width: | 14200NaN0 |
| Height: | 15500NaN0 |
| Weight: | 6500NaN0 with saloon body |
| Designer: | Alfred Böning |
| Sp: | uk |
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 801NaN1 stroke, generating a displacement of 7881NaN1.[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.
The 3/20 was larger than the 3/15, with an 84.60NaN0 wheelbase and a body 30NaN0 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. The standard bodies for the car were built by Daimler-Benz in Sindelfingen.
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.