The cylinder block is cast from aluminum alloy and is integral with the upper part of the crankcase. The block has a water jacket cavity open upwards, into which cast-iron sleeves are inserted with support in the bottom of this cavity
There are ten bosses along the contour of the upper plane of the block for attaching the cylinder head. The lower (crankcase) part of the block is divided into four compartments by transverse partitions into which the crankshaft main bearings are installed.
The main bearing caps are made of ductile iron, each cap is attached to the block with two 12mm diameter studs.
In the first cover, the ends are machined together with a block for installing thrust bearing washers
Bearing caps are bored assembled with the block, and therefore, when repairing, they must be installed in their places.
To facilitate installation, all covers, except for the first and fifth, have their serial numbers engraved.
The nuts of the cap fastening studs are tightened with a torque wrench with a torque of 100-110 Nm (10-11 kgm) and locked with sealant.
To the front end of the block on a paronite gasket, a cast aluminum alloy cover of timing gears with a rubber cuff to seal the crankshaft toe is attached
Attached to the rear end of the block is a cast aluminum alloy clutch housing with six bolts and two dowel pins, which must be accurately fitted for proper transmission operation.
The rear end of the clutch housing and the hole in it for installing the gearbox in order to ensure the alignment of the input shaft of the gearbox with the crankshaft are machined assembled with the block, so these parts are not interchangeable.
Engine cylinders are made in the form of easily removable wet liners, cast from special wear-resistant cast iron.
The cylinder liner is inserted into the block socket at the bottom.
In the plane of the lower joint, the sleeve is sealed with a soft copper gasket 0.3 mm thick, and along the upper end - with a cylinder head gasket.
For proper sealing, the upper end of the sleeve protrudes 0.02-0.1 mm above the plane of the block. In this case, the copper gasket must be crimped.
For reliable sealing, it is necessary that the difference in the protrusion of the liners above the plane of the block on one engine be within 0.02-0.055 mm.
This is achieved (at the factory) by sorting cylinder liners by height (from the lower joint to the upper end) and blocks by the depth of the groove under the sleeve (from its upper end) into two groups.
When changing cylinder liners, uniform protrusion can be ensured by selecting copper gaskets of the appropriate thickness
Cylinder head - common to all cylinders, cast from aluminum alloy and subjected to heat treatment (hardening and aging)
The inlet and outlet channels are made separately for each cylinder and are located on the right side of the head. The valve seats are arranged in a row along the longitudinal axis of the engine
All valve seats are plug-in, made of heat-resistant high-hardness cast iron
Due to the large tightness when seating the seat in the head seat (at the factory, before assembly, the head is heated to a temperature of 160-175 ° C, and the seats are cooled to approximately minus 40-45 ° C, while the seat is freely inserted into the head seat), and also, a sufficiently large coefficient of linear expansion of the seat material ensures a reliable and durable fit of the seat in the seat.
In addition, the metal of the head around the seats is crimped using a mandrel.
Valve bushings, like the seats, are assembled with the head preheated (the bushings are cooled) Chamfers in the seats and holes in the bushings are machined assembled with the head
The cylinder head is attached to the block with ten steel studs with a diameter of 12 mm. Heat-strengthened flat steel washers are placed under the stud nuts
A gasket made of asbestos cloth reinforced with a metal frame and a window covered with graphite in the gasket for the combustion chambers is installed between the head and the block, and the oil channel hole is edged with tin
The thickness of the gasket in the compressed state is 1.5 mm
The correct position of the head on the block is ensured by two dowel pins-sleeves pressed into the cylinder block (into the bosses of the head mounting studs).
The tightening torque of the cooking fastening nuts should be 83-90 Nm (3.3-9.0 kgm)
The cylinder heads of the 4025 and 4026 engines differ in the volume of the combustion chambers
The increase in the compression ratio of the 4026 engine was obtained by additional milling of the lower plane of the head by 3.6 mm (the height of the engine head 4026 is 94.4 mm, the height of the engine head 4025 is 93 mm)
Combustion chamber volume with valves in place and the screwed candle is 74-77 cm3 for the 4026 engine and 94-98 cm3 for the 4025 engine The difference between the volumes of the combustion chambers of one head should not exceed 2 cm3