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Kemp (Grey Eagle) I-4 or D-4, In-line 4 Engine


Display Status:

This object is on display in the Early Flight exhibition at the National Air and Space Museum in Washington, DC.

Collection Item Summary:

The Kemp Machine Works of Muncie, Indiana built several types of air-cooled engines for airplanes, motorcycles, ice boats, and air-drives for boats. Due to its simple design and quantity production, this engine sold for approximately one half the price of its water-cooled competitors, and was lighter, more streamlined, and trouble-free than most of them.

Early models such as this one had concentric valves, which presented a large valve area, but a complicated design. Later models were equipped with conventional valves. All of the 2-, 4-, and 6-cylinder models had automatic intake valves.

A Kemp Model D-4 powered Walter Ralston's 1912 biplane.

Collection Item Long Description:

Data Source

National Air and Space Museum


Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum

Credit Line

Gift of Mrs. L. L. Walker Houston, TX.




  • 3-D: 76 × 30 × 46cm (29 15/16 × 11 13/16 × 18 1/8 in.)
  • Support: 72.4 × 73.7 × 47cm (28 1/2 in. × 29 in. × 18 1/2 in.)

Country of Origin

United States of America



Physical Description

  • Type: Reciprocating, in-line, 4 cylinders; air-cooled, concentric valves; automatic inlet valve
  • Power rating: 26 kW (35 hp) at 1,150 rpm
  • Displacement: 4.18 L (255.36 cu in.)
  • Bore and Stroke: 108 mm (4.25 in.) x 108 mm (4.25 in.)
  • Weight: 82.2 kg (181 lb)


PROPULSION-Reciprocating & Rotary

Inventory Number