D-400 engine

The D-400 series engine or the Iron Horse engine was a light-duty two-stroke engine used for powering lawnmowers produced from the 1950s to the late 1970s. D-400 engines were single-cylinder engines designed and manufactured by the Outboard Marine Corporation (OMC; Johnson and Evinrude) for Lawn-Boy[2] and Masport. The D-400 engines displaced 109 cc, generated 2.61 kW of power, and operated in the range of 2400-3300 RPM.[1][3] The engines have a distinctive rectangular cowling that has created a nickname of Brick-top mowers. Another distinctive feature is the two-finger vertical recoil starter.[3] The kidney-shaped muffler and exhaust unit is mounted beneath the mowers' deck and gives the engine a small, low profile design when compared to the newer and more powerful lawnmower engines. The ignition system employs a magneto, points, and a condenser (capacitor) set-up with an unusual spark-advance system which utilised a weight on the crankshaft to adjust the spark-advance amount depending on engine speed. The sprung governor was also unusual with a throw-yoke which operated under the flywheel and was linked to the throttle. The carburetor was a float design and fed into a pair of reed valves.

D-400 series engine
Restored Masport Iron Horse engine
Overview
Manufacturer	Outboard Marine Corporation (OMC) Lawn-Boy
Also called	Iron Horse
Production	1954--1977
Layout
Configuration	Single-cylinder 2-stroke
Displacement	108.99 cc (6.651 cu in)[1]
Cylinder bore	60.325 mm (2.3750 in)
Piston stroke	38.1 mm (1.50 in)
Block material	Aluminum
Head material	Aluminum
Compression ratio	4.5:1
Combustion
Fuel system	Float carburetor
Fuel type	Petrol
Oil system	16:1-32:1 pre-mixed fuel:oil mix
Cooling system	Air-cooled
Output
Power output	2.6 kW (3.5 hp)[1]
Chronology
Successor	D-600

The D-400 engines are now a popular engine restoration job due to their distinctive shape and low cost.[4][5] Parts, however can be difficult to source and therefore multiple engines are often bought to satisfy part requirements. The recommended oil:fuel mix is either 16:1 or 32:1 depending on age.[1] In New Zealand and Australia, Masport also known in New Zealand as "Charlie Gamble" offered the D-400 engine on their Premier, Premier II, Rancher, Rotacut, and Tornado models.[6] In this Oceania market, the D-400 was called the Iron Horse engine.

References

1. Lawn-Boy (1983). "Lawn-Boy Service Manual 1950--1983". Retrieved 2012-02-04.
2. "Lawn-Boy brand history". 2012. Archived from the original on 2012-02-13. Retrieved 2012-02-04.
3. "Lawn Boy Engine series". 2008. Retrieved 2012-02-04.
4. "1977 Lawnboy 5024 Restored by Yard Nazi". 2012. Retrieved 2012-02-04.
5. Pcamore (2011). "Finished my Renovation 2 Stroke Masport Iron Horse". Retrieved 2012-02-04.
6. "Moving Up to Masport TV Commercial [sic] (1972)". 2011. Retrieved 2012-02-04.