Bedford TM 4400
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The Detroit Diesel engine fitted to Bedford's 38-tonne TM 4x2 tractive unit had a relatively modest power output compared to many of the other machines we had been testing at the new maximum weight.
A net installed 1 9 8 kW (265bhp) power output is backed up by a healthy torque of 1,276Nm (934 lbft) which hardly falls off at all between 1,000 and 1,60Orpm.
To improve light load fuel economy a Belleville washer is fitted to the governor to restrict fuel delivery at engine speeds above 1,600rpm. It did not appear to impair the vehicle's hill climbing ability as it is only effective at speeds above which maximum torque occurs.
A throttle delay mechanism might also have helped in economising on the rate of fuel consumed. However, it proved troublesome on the test vehicle preventing the full fuel position from being reached during track tests.
Big brakes gave a good, controlled response and a Jacobs brake provided a worthwhile retardation from the engine.
The lightweight two-stroke engine complements the lightweight chassis and provides for an excellent payload of 24.78 tonnes when coupled to CM's York tri-axle trailer. A fuel return of 42.671it/100km (6.62mpg) is a significant improvement over past performances with Detroit Diesel engines.