2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42
Diesel engines of models 236 and 238 were developed by the designers of the Yaroslavl Motor Plant and replaced the outdated family of YaMZ 204/206 two-stroke engines. The fundamental difference between the new engines was a four-stroke cycle of operation, which significantly increased the performance of the engines. In the design of the units, a scheme with a V-shaped arrangement of cylinder blocks was used, while the YaMZ 236 engine had six cylinders, and the YaMZ 238 had eight. There are two YaMZ 236 engines in the photo, the fuel pump is clearly visible, above which the air supply manifolds are located. The hole for installing the air filter is sealed with protective paper.
Cylinder block
Two cylinder blocks have an angle of 90 degrees between them and a common base, which is the upper part of the crankcase. To simplify the design, the connecting rods of opposite cylinders are mounted on the same crankpin of the crankshaft. For layout considerationsthe cylinder axes are offset by 35 mm. The cylinder block is made of gray cast iron with a low amount of alloying elements. When calculating the block, special attention was paid to ensuring rigidity, which made it possible to achieve high technical characteristics of the YaMZ 236 engine.
Replaceable liners are installed in the cylinder blocks, the so-called wet type - the coolant washes the outer part of the liners. The block has bearings for the bearings of the camshaft and crankshaft. The processing of the crankshaft bearing beds is carried out with the covers installed. Therefore, covers are not interchangeable and must be installed in a strictly defined position.
In the front part of the block, the housing of the gear block of the gas distribution mechanism drive is installed, in the rear part, the flywheel housing, made as a separate part, is fixed. A coolant pump is mounted on the gear housing cover. Fluid from the pump is pumped into the cylinder blocks through a channel in the cover and gear housing. Inside the cover there are additional channels for the coolant. The gear cover has a milled plane with hatch marks, used in conjunction with a mark on the crankshaft pulley to set the fuel injection start point. False installation of labels is an indispensable condition for ensuring the technical characteristics of YaMZ 236.
Cylinder heads and timing system
Each block YaMZ 236 has a separate head for three cylinders. The head is made of cast iron and is attached to the block with steel studs. Block and head have a common shirtcooling, which ensures a uniform temperature regime of the engine. A gasket is installed between the parts, on early models made of asbestos with metal edging of the cylinder bores and a coolant duct.
Each cylinder has two valves. The valves are driven by rocker arms and rods from a single camshaft installed in the collapse of the cylinder blocks. Shaft drive - from the toe of the crankshaft through several helical gears. The camshaft is installed according to the marks on the gears. In the photo located in the article, the YaMZ 236 engine with the valve cover removed.
The head is equipped with a nozzle for fuel injection and a pipe for returning excess fuel to the fuel tank. From above, the head is closed with a thin-walled cap.
Piston group and crankshaft
Technical characteristics of YaMZ 236 are provided by a crankshaft with four main bearings made of high carbon steel. Thanks to this design and material, the shaft has high rigidity and high wear resistance. Inside the crankshaft there are channels for supplying oil under pressure to the main and connecting rod bearings. The shaft design uses additional counterweights on the cheeks and two separate counterweights on the shaft toe and flywheel. There is a groove in the rear support, which includes bronze half-rings that protect the shaft from axial displacements. Both ends of the shaft have sealing glands. Installed in the toe of the shaftremovable timing gear.
Engine connecting rods are steel with non-interchangeable bearing caps. YaMZ 236 pistons are made by casting from aluminum alloy and have five grooves for piston rings. The piston casting has a combustion chamber made in the shape of a toroid. The three compression rings are trapezoidal in cross section. All parts of the piston group are divided into size groups, which makes it easier to select parts for repairs.
Lubrication system
The oil reservoir of the YaMZ 236 engine is the oil pan. From there, the oil enters the gear pump and is supplied under pressure to the crankshaft and camshaft bearings, the upper heads of the connecting rods, rocker arms and valve drive rods. The pump can pump up to 140 liters of oil per minute. The rest of the engine components are lubricated by the oil mist generated during engine operation. In total, the lubrication system contains 24 liters of oil. Cleaning takes place in two stages - a coarse filter and a centrifugal product for fine cleaning. About 10 percent of the oil pumped by the pump passes through the centrifuge. After cleaning, it flows back into the crankcase. Maintenance of the centrifuge consists in washing the internal cavity from settled dirt. The coarse filter is a brass fine mesh. When servicing the motor, the mesh is simply washed and reinstalled. The technical characteristics of YaMZ 236 directly depend on the performance of the lubrication system.
When the engine is running, it is necessary to monitor the oil pressure, which shouldbe within 4 … 7 atmospheres. In hot weather, the pressure may decrease slightly due to the high temperature of the engine oil. Additional oil cooling is carried out using a separate radiator located in front of the coolant radiator. At the maximum operating mode, up to 25 liters of oil passes through the device per minute. The oil cooled in the radiator is drained into the engine crankcase.
Cooling and power system
Maintaining the temperature regime is an indispensable condition for ensuring the technical characteristics of the YaMZ 236 engine. Fuel and oil consumption, as well as engine durability, are directly dependent on engine temperature. To maintain the temperature regime, the engine is equipped with a radiator with a special valve that allows you to increase the boiling point of the coolant to 116-119 degrees.
The liquid is cooled by a six-blade fan driven by the timing gears. An intermediate pulley for driving the generator and the compressor of the pneumatic brake drive system is installed on the fan shaft on bearings. The fan is installed in a special casing that directs the air flow. The intensity of cooling is regulated by manually operated blinds installed in front of the radiator from the driver's cab. The engine is connected to the radiator with rubber hoses. The total capacity of the system is 28 liters. The photo in the article shows a general view of the YaMZ 236 with a turbocharger and gearbox.
Operating temperatureengine is the range of values within 75-98 degrees. Each block of cylinders has its own channel for the removal of liquid, equipped with a thermostat. The manufacturer does not recommend prolonged operation of the engine at a coolant temperature below 60 degrees. The temperature is controlled by the instrument on the dashboard in the driver's cab.
Optionally, a PZhD 400 or 44 model heater can be installed in the cooling system. The heater is installed in front of the radiator and is based on heating the liquid with fuel burning in the boiler. There are special channels for installing a heater in the YaMZ 236 engine block. The fluid is circulated by a separate electrically driven pump. Exhaust gases are directed to the oil pan to heat up the oil. The use of an autonomous heater improves the operational and technical characteristics of YaMZ 236. Fuel consumption when using such a system is noticeably lower, especially when operating a diesel engine at low temperatures.
Power system
The system includes a high pressure pump with speed control, fuel filters, injection nozzles and low and high pressure fuel lines. For filtration, coarse and fine filters are used. One of the photos in the article shows a modern version of the YaMZ 236 with a turbocharger and a 9-blade fan.
Due to the improved design, the specific fuel consumption of the enginedecreased. If on the first MAZ 500 the consumption was about 25 liters with a power of only 180 hp, then on modern cars it is 33-40 liters with a power of 300 to 420 hp.
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