General view and cross section of the engines are shown in the figures.

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

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

Cylinder block 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.

ZMZ-402 on the left side

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

The oil sump is attached to the block from below, the cylinder head is attached to the top.

Cross section of ZMZ-402

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 head of the block on the racks. Seats and valve guides are installed in the block head 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. From above, the head of the block is closed with a cover stamped from sheet steel.

ZMZ-402 on the right side

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 top compression ring is cast from ductile iron. The working surface of this ring is coated with a layer of chromium to increase wear resistance.

The working surface of the lower compression ring, cast from gray cast iron, is coated 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 piston bottom.

The oil scraper ring consists of four elements: two steel discs and two expanders, axial and radial. The working surface of the disks 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 I-section shank.

Tin bronze bushing is pressed into the top end of the connecting rod. The lower head 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 input shaft of the gearbox.

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