The general view and cross section of the engines are shown in the figures.
The engines are inline four-cylinder, equipped with carburetors and a contactless ignition system
Both are similar in design, but the mod. 4021 engine is deformed.
The cylinder block is cast from aluminum alloy.
Cylinder liners cast from wear-resistant cast iron are inserted into it.
In the lower part of the block, five main bearing supports are made.
The caps of the main bearings are made of ductile iron and are attached to the block with two studs.
Bearing covers are processed together with the block, so they cannot be swapped.
The cover of the first bearing is processed along the ends together with a block for installing two thrust washers to limit the axial movement of the crankshaft.
Their serial numbers are stamped on the covers of the 2nd, 3rd and 4th bearings.
The front end of the block is attached to the cover of the distribution gears, cast from aluminum alloy, into which the crankshaft cuff is inserted.
The clutch housing is attached to the rear end of the block.
An oil sump is attached to the block from below, and the cylinder head is attached from above.
The block head is cast from aluminum alloy.
Intake and exhaust valves are installed vertically in it.
The valves are driven from the camshaft located in the cylinder block through pushrods, rods and rocker arms.
The axis of the rocker arms of the valves is installed in the block head on the racks.
Seats and valve guide bushings are installed in the head of the block with a large tension.
Combustion chambers are made in the lower part of the block head.
The heads of the engine blocks mod. 402 and 4021 differ in the volume of the combustion chambers and height.
The height of the engine block head mod. 402 is 94.4 mm, mod. 4021 — 98 mm.
The top of the block head is closed with a stamped sheet steel lid.
The pistons are cast from aluminum alloy, the bottom of the piston is flat.
To properly install the piston in the cylinder, the inscription "Before" is cast on the side wall of the boss under the piston pin.
The piston is installed in the cylinder so that this inscription is facing the front of the engine.
Two compression rings and one oil removal ring are installed on each piston.
The upper compression ring is cast from high-strength cast iron.
The working surface of this ring is coated with a layer of chrome to increase wear resistance.
The working surface of the lower compression ring, cast from gray cast iron, is covered with a layer of tin, which improves its running-in.
There is a groove on the inner surface of this ring.
The ring should be installed with this groove up to the bottom of the piston.
The oil ring consists of four elements: two steel discs and two expanders, axial and radial.
The working surface of the discs is covered with a layer of chrome.
The piston is attached to the connecting rod with a piston finger of the "floating" type, i.e. the finger is not fixed either in the piston or in the connecting rod.
The finger is kept from moving by two spring locking rings, which are installed in the grooves of the piston bosses.
The connecting rods are forged steel, with an I-beam rod.
A tin bronze bushing is pressed into the upper head of the connecting rod.
The lower connecting rod head with a cover, which is fastened with two bolts.
The nuts of the connecting rod bolts are locked with a sealant "Unigerm-9".
Connecting rod covers are processed together with the connecting rod, so they cannot be moved from one connecting rod to another. Cylinder numbers are stamped on the connecting rods and connecting rod covers.
A hole is made in the connecting rod rod at the lower head to lubricate the cylinder mirror.
This hole should be directed to the right in the direction opposite to the camshaft.
The mass of pistons assembled with a connecting rod should not differ by more than 12 g for different cylinders.
Thin-walled connecting rod inserts are installed in the lower head of the connecting rod.
The crankshaft is cast from high-strength cast iron.
The shaft is kept from axial movement by thrust washers mounted on the front neck.
In the rear end of the shaft there is a socket for installing the ball bearing of the primary shaft of the gearbox.
A flywheel cast from gray cast iron is attached to the rear end of the crankshaft with four bolts.