Design features of the ZMZ-402 engine

ZMZ-402 and ZMZ-4021 Engines

The general view and cross-section of the engines are shown in the figures.

The engines are in-line four-cylinder units equipped with carburettors and a contactless ignition system.

Both are similar in design, but the Mod. 4021 engine is derated.

The cylinder block is cast in aluminium alloy.

Cylinder liners cast in wear-resistant cast iron are inserted into it.

View of the Mod. 402 and 4021 engines from the left-hand side: 1 — starter motor; 2 — starter solenoid; 3 — oil line; 4 — fuel pump; 5 — engine mounting bracket; 6 — oil pressure warning lamp sensor; 7 — oil filter; 8 — crankshaft pulley; 9 — water pump pulley; 10 — water pump; 11 — thermostat; 12 — coolant temperature gauge sensor; 13 — fine fuel filter; 14 — spark plug; 15 — ignition distributor; 16 — tappet cover; 17 — ignition distribution and oil pump drive

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

The main bearing caps are made of malleable cast iron and are secured to the block by two studs.

The bearing caps are machined together with the block, so they must not be interchanged.

The cap of the first bearing is machined on its end faces together with the block to accommodate two thrust washers limiting the axial movement of the crankshaft.

The caps of the 2nd, 3rd and 4th bearings are stamped with their sequence numbers.

The timing gear cover, cast in aluminium alloy and containing the crankshaft oil seal, is attached to the front end of the block.

The clutch housing is attached to the rear end of the block.

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

The cylinder head is cast in aluminium alloy.

View of the Mod. 402 and 4021 engines from the right-hand side: 1 — crankshaft pulley; 2 — oil pressure gauge sensor; 3 — exhaust manifold; 4 — oil sump; 5 — coolant drain cock; 6 — cylinder head; 7 — intake pipe; 8 — carburettor; 9 — oil filler cap; 10 — rocker cover; 11 — thermostat; 12 — water pump pulley; 13 — alternator

In it the intake and exhaust valves are mounted vertically.

The valves are actuated from the camshaft located in the cylinder block, through tappets, pushrods and rockers.

The valve rocker shaft is mounted in the cylinder head on pillars.

The valve seats and valve guides are installed in the cylinder head with a heavy press fit.

The combustion chambers are formed in the lower part of the cylinder head.

The cylinder heads of the Mod. 402 and 4021 engines differ in combustion chamber volume and height.

The cylinder head height of the Mod. 402 engine is 94.4 mm, Mod. 4021 — 98 mm.

On top the cylinder head is closed by a cover pressed from sheet steel.

The pistons are cast in aluminium alloy, the piston crown is flat.

Cross-section of the Mod. 402 and 4021 engines: 1 — oil pump; 2 — oil sump; 3 — oil drain plug; 4 — connecting rod cap; 5 — crankshaft; 6 — main bearing cap; 7 — connecting rod; 8 — piston; 9 — cylinder liner; 10 — exhaust manifold; 11 — intake pipe; 12 — valve guide; 13 — valve; 14 — oil separator of the crankcase ventilation system; 15 — rocker shaft cover; 16 — valve rocker; 17 — rocker shaft; 18 — tappet pushrod; 19 — ignition distributor; 20 — distributor drive; 21 — tappet; 22 — camshaft; 23 — starter motor

For correct installation of the piston in the cylinder, the inscription «Перед» (Front) is cast on the side wall near the piston pin boss.

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

Two compression rings and one oil control ring are fitted to each piston.

The upper compression ring is cast in high-strength cast 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 in grey 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 must be installed with this groove upwards, towards the piston crown.

The oil control ring consists of four elements: two steel discs and two expanders, axial and radial.

The working surface of the discs is coated with a layer of chromium.

The piston is connected to the connecting rod by a «floating» type piston pin, i.e. the pin is fixed neither in the piston nor in the connecting rod.

The pin is retained against displacement by two spring circlips installed in grooves in the piston bosses.

The connecting rods are steel forgings with an I-section shank.

A tin bronze bush is pressed into the upper connecting rod eye.

The lower connecting rod eye has a cap secured by two bolts.

The connecting rod bolt nuts are locked with «Unigerm–9» sealant.

The connecting rod caps are machined together with the rod, so they must not be transferred from one rod to another. The cylinder numbers are stamped on the connecting rods and caps.

A hole for lubricating the cylinder bore is provided in the connecting rod shank near the lower eye.

This hole must face to the right, to the side opposite 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 bearing shells are installed in the lower connecting rod eye.

The crankshaft is cast in high-strength cast iron.

The shaft is retained against axial movement by thrust washers mounted on the front journal.

In the rear end face of the shaft there is a seat for mounting the ball bearing of the gearbox input shaft.

The flywheel, cast in grey cast iron, is secured to the rear end of the crankshaft by four bolts.