KrAZ-256

KrAZ-256 at a glance: maker, years and purpose

KrAZ was set up in Kremenchuk to build heavy trucks, taking over production from an older plant in the late 1950s. Its first dump truck, the KrAZ-222 "Dnipro" (1959–1966), used a two-stroke diesel. The KrAZ-256 kept the proven bonneted layout and chassis but introduced a modern four-stroke V8, and it became the standard heavy dump truck of Soviet quarries, mines, oil fields and large construction sites. The plant's story is told in the history of KrAZ, and its trucks are listed in the KrAZ catalogue.

History and development

In 1959 the Soviet leadership instructed engine makers to replace two-stroke diesels with more economical four-stroke engines. The result was the YaMZ family of 1960–1961: the six-cylinder YaMZ-236, the eight-cylinder YaMZ-238 and the twelve-cylinder YaMZ-240. The V8 YaMZ-238 was chosen for the new KrAZ dump truck. A first batch was built in 1961, and series production of the KrAZ-256 began in 1966, with the improved 256B soon becoming the main version.

The KrAZ-256 was designed for roads of the first and second category with axle loads of up to 10,000 kg, but in practice most trucks worked in quarries and on construction sites. It was valued for its simplicity, strength and tolerance of overloading. KrAZ adapted export trucks to local conditions: right-hand-drive versions went to sand quarries in England, tropical versions to southern countries, and cold-climate versions with double-glazed cab windows, frost-resistant rubber and an engine pre-heater to northern markets. By 1978 the KrAZ-256 had been exported to 55 countries.

By the mid-1970s the design was ageing. Its heavy controls, rolled-channel frame and wood-and-metal cab compared poorly with later Western and Czechoslovak trucks such as Magirus-Deutz and Tatra models. A planned successor, the KrAZ-251, was postponed, and a modern replacement arrived only with the KrAZ-6510 in the 1990s.

Cab and body

The three-seat cab sits behind the engine. The driver's seat is sprung and adjustable for reach, weight, backrest angle and height, and there is room for two passengers. In 1969 the headlights and indicators were moved into boxes on the front wings; at the end of the 1970s their mounting was simplified.

The standard body is a bucket-type quarry body without a tailgate, tipped rearwards by two hydraulic cylinders. It lifts in about 20 seconds and lowers in about 30 seconds. Flatbed versions were also built on the same chassis, but they were not developed further.

Engine, gearbox and running gear

The front axle sits on two semi-elliptic leaf springs with rubber-cushioned ends; the rear bogie uses a balanced suspension on semi-elliptic springs with sliding ends, which improves ride on rough ground. Steering is screw-and-ball-nut with a toothed sector and hydraulic power assistance.

The air brakes use 440 mm drums and two circuits: one for the front and middle axles and one for the rear. The parking brake is a mechanically operated drum on the transmission. The early brake system had a known weakness: on long descents with the engine idling, the compressor and power steering pump slowed down, air pressure fell and the truck became hard to stop. The 256B1 of 1978 added split brake circuits and other improvements.

KrAZ-256 specifications

KrAZ-256 versions and modifications

Some operators also converted trucks into tractor units for towing heavy trailers.

In service: strengths and weaknesses

Strengths:

• Strong, simple design that tolerates overloading and extreme temperatures.
• Fast tipping body and good approach and departure angles.
• Easy maintenance and wide availability of parts, many still made today.

Weaknesses:

• High fuel consumption and heavy controls that tire the driver.
• Limited visibility past the long bonnet and a dated cab.
• Rear-wheel drive only, so it can get stuck on soft ground.
• Brake weaknesses on early trucks.

The KrAZ-256 and the Kremenchuk plant

The dump truck grew up with the plant. KrAZ was already exporting its trucks early on: by 1961 more than 500 vehicles had gone to 26 countries, including Argentina, Bulgaria, China, India and Vietnam. With the KrAZ-256B as one of its main products, the plant built its 100,000th truck in 1968 and its 500,000th in 1984, and annual output reached 30,655 vehicles in 1986. The 256B1 of 1978 reflected the lessons of the first decade, with a longer service life between overhauls, split brake circuits and a starting pre-heater as standard. Its successor, the KrAZ-6510, went into production in 1992, also as a 6×4 dump truck, with a 179 kW (240 hp) engine.

Successors and legacy

The KrAZ-256 was the first mass-produced heavy dump truck of its class in the Soviet Union and remained in production for almost three decades. Its components and layout were shared with the all-wheel-drive KrAZ-255 and later the KrAZ-260, and its role passed to the KrAZ-6510. Many trucks still work in quarries, and spare parts are still made both at KrAZ and by other suppliers. More heavy vehicles are listed among trucks.