Section 6. Postwar Arrangements and Labor Disputes

Item 5. U.S. Army Vehicle Repair Operations and Compact Car Development

As part of occupation policy, U.S. army vehicle repair operations were commissioned to automakers. As the repair operations purchasing order issued by the U.S. army was called a 'Procurement Demand' (PD), this work was referred to as PD Operations at Toyota Motor Co., Ltd.

In April 1947, a passenger car repair purchasing order was received from the U.S. Fifth Air Force and relevant operations began at the Koromo Plant. The operational procedure was to take the vehicle for repair to a disassembly station set up inside Machining Plant No. 3, where it was broken down into engine, frame, and body before being repaired part by part, then painted, coated, and reassembled at the assembly plant. In June of the same year, the Kariya-kita Plant also received a commission for jeep and truck repair from the U.S. Fifth Air Force and was engaged in the operation for around one year.

The Koromo Plant was again commissioned with repair operations in July 1948 and in October1949. However, in that same month, the ban on passenger car production was lifted. Toyota Motor Co., Ltd. joined in the return to passenger car manufacturing, and so U.S. army vehicle repair operations were terminated in March 1950. Up till then, approximately 300 vehicles had been repaired, most of them Chrysler passenger cars of the Plymouth model.

Immediately after the war, the occupying administration had forbidden passenger car production, but companies were free to carry out research and development. Toyota Motor Co., Ltd. started work in mid-October 1945 on the design of a compact car engine and completed the drawings in February 1946. Prototype production began immediately and, in November of the same year, the first prototype of the S engine was completed and mounted in the Model SB truck that went on sale in April 1947.

The structure of the various parts of the S engine were designed with reference to the Baby Ford made by Ford of Britain, while the main specifications and performance drew on the Trumpf-Junior made by the German firm Adler.1 Table 1-21 presents a comparison of the S engine with the Baby Ford and Adler engines.

The S engine was the only Toyota vehicle engine of the side valve type. From the first A engine through to the engine developed in 1945, Toyota vehicles had all been of the overhead valve type.2

Table 1-21. Specifications of the S Engine (1947)

S Engine
Baby Ford
Water-cooled inline, 4-cylinder, side valves
Total engine displacement volume
Compression ratio
Maximum output
Maximum torque
S engine: Toyota Technology, March 1, 1948, p. 30
Baby Ford (model Y): British Cars (1974), p. 129.
Adler (Adler 'Trumpf Junior'): Autos in Deutschland 1920-1939 (1963), p. 22.

However, in order to create some parts in common with the engines of Nissan Motor Co., Ltd., there had in fact been a plan to develop a six-cylinder side valve engine. According to a design order dated September 10, 19413 he side valve engine was to be easy to produce, but was also required to have superior performance and improved fuel efficiency. The design phase of this side valve engine was completed in 1943 as the L engine4 (six-cylinder, 3,790 cc), but did not progress to prototype production.

The design engineer in charge of S engine development at the time explained that the reason for adopting the side valve format was that even greater simplicity and solidity was demanded.5 There was a shortage of materials for vehicle manufacturing due to the rationing system and manufacturing had to make do with existing facilities. The choice of the side valve format with its simple structure and small number of parts was therefore a natural adaptation to the circumstances of the time.

Vehicles fitted with the S engine are discussed below in “Development of Compact Car Equipped with the S Engine” (Section 8 Item 1).

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