ZMZ-402 engines are installed on Volga, UAZ, Gazelle cars

The engines have proven themselves well during operation. Unpretentious and easily repaired, in garage conditions.

Inline four-cylinder engines equipped with carburetors and contactless ignition system.

Both are similar in design, but the engine mod. 4021 deformed.

View of the engine from the left side: 1 - starter; 2 - traction relay; 3 - oil pipeline; 4 - fuel pump; 5 - engine support bracket; 6 - emergency oil pressure sensor; 7 - oil filter; 8 - crankshaft pulley; 9 - water pump pulley; 10 - water pump; 11 - thermostat; 12 - coolant temperature indicator sensor; 13 - fuel fine filter; 14 - spark plug; 15 - ignition distributor; 16 - pusher cover; 17 - ignition distributor and oil pump drive

Fig. 1. Type of engines mod. 402 and 4021 on the left side

View of the engine from the right side: 1 - crankshaft pulley; 2 - oil pressure indicator sensor; 3 - exhaust manifold; 4 - oil sump; 5 - coolant drain valve; 6 - cylinder head; 7 - inlet pipe; 8 - carburetor; 9 - oil filler cap; 10 - cover of the valve mechanism; 11 - thermostat; 12 - water pump pulley; 13 - generator

Fig. 2. Type of engines mod. 402 and 4021 on the right side

Cross section of the engine: 1 - oil pump; 2 - oil sump; 3 - oil drain plug; 4 - connecting rod cover; 5 - crankshaft; 6 - main bearing cover; 7 - connecting rod; 8 - piston; 9 - cylinder sleeve; 10 - exhaust manifold; 11 - inlet pipe; 12 - valve guide sleeve; 13 - valve; 14 - oil cleaner of the crankcase ventilation system; 15 - valve lever axis cover; 16 - valve lever; 17 - axis of valve levers; 18 - pusher rod; 19 - ignition distributor; 20 - ignition distributor drive; 21 - pusher; 22 - camshaft; 23 - starter

Fig. 3. Cross section of engines mod. 402 and 4021

The cylinder block is cast from an aluminum alloy. Cylinder liners cast from wear-resistant cast iron are inserted into it.

Five main bearing supports are made in the lower part of the block.

The main bearing caps are made of ductile iron and are attached to the block with two studs.

The bearing caps are processed together with the block, so they cannot be interchanged.

The cover of the first bearing is machined at the ends together with a block for installing two thrust washers to limit the axial movement of the crankshaft.

On the covers of the 2nd, 3rd and 4th bearings, their serial numbers are stamped.

At the front end of the block, a timing gear cover is attached, cast from an aluminum alloy, into which the crankshaft collar 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 a cylinder head is attached to the top.

The head of the block is cast from an aluminum alloy. It has vertically mounted intake and exhaust valves.

The valves are driven by a camshaft located in the cylinder block through pushers, rods and rocker arms.

The axis of the rocker arms is installed in the block head on racks.

Saddles and valve guides are installed in the head of the block with a large interference fit.

Combustion chambers are made in the lower part of the block head.

Engine block heads mod. 402 and 4021 differ in combustion chamber volume and height.

Height of engine block head mod. 402 is equal to 94.4 mm, mod. 4021 - 98 mm.

At the top, the head of the block is closed with a cover stamped from sheet steel.

The pistons are cast from aluminum alloy, the piston bottom is flat.

For the correct installation of the piston in the cylinder, the inscription "Front" is cast on the side wall near the boss under the piston pin.

The piston is installed in the cylinder so that this inscription is facing the front of the engine.

Each piston has two compression rings and one oil scraper ring.

The upper compression ring is cast from ductile iron.

The working surface of this ring is coated with a layer of chromium for increased wear resistance.

The working surface of the lower compression ring, cast from gray cast iron, is coated with a layer of olova, which improves its running-in.

There is a groove on the inner surface of this ring.

The ring should be installed with this groove upwards, towards the piston bottom.

The oil scraper 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 "floating" type piston pin, i.e. the pin is not fixed either in the piston or in the connecting rod.

The finger is kept from moving by two spring retaining rings, which are installed in the grooves of the piston bosses.

Forged steel connecting rods, with an I-section rod. A tin bronze bushing is pressed into the upper end of the connecting rod.

The bottom end of the connecting rod with a cover that is attached with two bolts. The nuts of the connecting rod bolts are locked with Unigerm-9 sealant.

The connecting rod caps are machined 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 caps.

In the rod of the connecting rod at the lower head there is a hole for lubricating the cylinder mirror.

This hole should point to the right, away from the camshaft.

The mass of the pistons assembled with the connecting rod must not differ by more than 12 g for different cylinders.

Thin-walled connecting rod bearings are installed in the lower head of the connecting rod.

The crankshaft is cast from ductile iron.

The shaft is kept from axial movement by thrust washers mounted on the front journal.

At the rear end of the shaft there is a socket for installing the ball bearing of the gearbox input shaft.

A gray cast iron flywheel is attached to the rear end of the crankshaft with four bolts.