Section 4. Construction of the Automotive Department Assembly Plant and Koromo Plant

Item 8. Model B Engine, Model GB Truck Developed

In about October 1937, when the Model GA truck had been proved that it could withstand a certain degree of use, vehicle improvements were completely suspended and all efforts were directed toward construction of the Koromo Plant. In conjunction with the completion of the Plant, engines and vehicle series were completely updated.

The Chevrolet engine that was used as a model for development of the A engine was later improved and the output increased, so development of a new engine for Toyota vehicles was also undertaken. The design of A engine used imperial measurements to ensure compatibility with Chevrolet engine parts so service parts could be used. At around this time, the construction plan for the Koromo Plant was adopted and concerns regarding supplies of service parts were eliminated, so a decision was made to conduct new engine design using metric units with the premise that the new engine would use Toyota vehicle parts only.

Work on the design of the new engine started in about May 1937 and was completed in about October. Prototype production of the new engine, known as the B engine, began and full-scale production started from December with the completion of the Koromo Plant in November 1938. The main specifications and areas of improvement leading to the B engine are shown in Table 1-6.

Table 1-6. Comparison of the B Engine (1939) Specifications with the A Engine

B Engine
A Engine
Inline 6-cylinder, overhead valves
Diameter (bore)
84.14 mm
35/16 in (84.14 mm)
Travel (stroke)
101.6 mm
4 in (101.6 mm)
Cylinder volume (exhaust volume)
3389 cc
206.8 in3 (3,389 cc)
Compression ratio
Actual hp
75 hp
65 hp
22.0 kg-m
140 ft-lbs (19.4 kg-m)
Crankshaft bearing parts
Material of bearings
Special cast steel
Carbon steel (forged)
Camshaft bearing parts
Material of bearings
Special cast steel
Carbon steel (forged)
Intake valve
40 mm diameter, 30-degree seat angle
11/2 in diameter (38.1 mm), 45 degree seat angle
Exhaust valve
38 mm Diameter, 30-degree seat angle
113/32 in (35.72 mm), 45-degree seat angle
Cooling equipment

78 mm rotor diameter, 8-vane centrifuge pump, 19.7 liter coolant capacity
Force-feed circulating water-cooled, 69 mm diameter rotor, 4-vane centrifuge pump, 15.7 liter coolant capacity
Water jacket
Full cylinder length
Part of the cylinder
Oil supply equipment
Gear-type oil pump, pressure delivery, airborne droplet spray, jet-injection
Vane-type oil pump, pressure delivery, airborne droplet spray
Toyota Vehicle Handling and Repair Methods,' February 1, 1940; Streamline, issued February 1, 1939, pages 42-45; 'Anatomy of Domestically-Produced New Toyota Trucks', Ryusenkei, February 1, 1939, pp. 42-45.
The 'Toyota Vehicle Handling and Repair Methods' issued on March 1, 1940 indicated improved specifications with maximum output of 78 hp.

The B engine was used on the Model GB truck (released in 1939, an improved version of the Model GA truck), the Model AA passenger car (1939), the Model AC passenger car (1943, an improved version of the Model AA), the Model KB truck (1942), the Model KC truck (1943), the Model BM truck (1947), the Model BX (1951), and other vehicles. Maximum output was increased from 75 hp to 78 hp, and it was further improved to 85 hp in 1953. The B engine was produced until the end of 1956, when it was replaced by its successor, the F engine.

The Model GB truck equipped with the B engine was launched at dealers nationwide on January 15 and 16, 1939. At the time of the development, improvement to the Model GA truck was suspended to focus on the Model GB truck, and the improvements to the GA were reflected in the GB. Production of the Model GA truck continued until September 1940 to use up inventories of parts.

Various improvements to the Model GB truck included the steering worm gear (improved machining precision), the front springs (improved strength), the spring hangers (improved strength), and adoption of an X member frame (increased frame rigidity). The specifications of the Model GB truck chassis compared to the Model GA are shown in Table 1-7.

Table 1-7. Specifications of the Model GB Truck (1939)

Model GB Truck Chassis
Model Gab Truck Chassis
Type B (3,389 cc, 75 hp)
Model A (206.8 in3 (3,389 cc), 65 hp)
3.609 m
1411/2 in (3.594m)
5.786 m
237 in (6.02m)
2.051 m
803/4 in (2.050m)
Empty weight
1,720 kg
2,936 lbs (1,332 kg)
'Toyota Truck Specification Sheet' (model GA: 1937; Model GB: 1939), Toyota Truck catalog.

The GB truck was a substantial improvement from the GA truck, but there were still problems with the performance, and the efforts to improve the performance were as discussed above.

To top of page