The gaps between the rocker arms and valves are adjusted on a cold engine, with the cylinder head fastening nuts and the nuts fastening the racks of the rocker arm axles are tightened to the required torque

The adjustment of the thermal gap between the valves and rocker arms is performed when repairing the cylinder head.

It is necessary to adjust the valve clearances after replacing the valve stem seals. Also, when there is a knock in the area of ​​​​the valve cover.

Adjusting the thermal clearance of the ZMZ-402 engine valves

With an increased gap, a characteristic sonorous metallic sound appears.

With a small gap between the valves and the rocker arms, the engine will seem to be "clamped", or they say - "dumb". At the same time, its power and throttle response will be reduced, as well as increased wear of the valve mechanism.

Adjustment is carried out on a cold engine.

The engine is considered conditionally cold when its temperature equals the ambient temperature.

To make it easier to scroll the crankshaft, you need to unscrew the candles.

It is easier to navigate when scrolling the crankshaft if the cover of the distributor is open.

On the body of the distributor with a felt-tip pen, we make marks that correspond to the position of the pistons at TDC when the distributor slider approaches each contact of the distributor cap.

ZMZ-402 valve clearance adjustmentZMZ-402 valve clearance adjustment

Remove the carburetor air filter housing for this:

Loosen the clamp with a screwdriver and remove the crankcase exhaust hose.

We “snap off” five clips, and remove the cover of the air filter housing, take out the filter element.

ZMZ-402 valve clearance adjustment

Loosen the clamp with a screwdriver and remove the corrugated air intake hose.

ZMZ-402 valve clearance adjustmentZMZ-402 valve clearance adjustment

With a screwdriver we bend the antennae of the lock washers, and with a 10 key we unscrew the three nuts.

Remove the air filter housing.

ZMZ-402 valve clearance adjustmentZMZ-402 valve clearance adjustment

Disconnect the crankcase exhaust pipe.

Disconnect the vacuum regulator hose of the ignition distributor sensor

ZMZ-402 valve clearance adjustmentZMZ-402 valve clearance adjustment

Using a 10 socket wrench, we unscrew the six bolts of the block head cover

Remove the cover

Remove the gasket

ZMZ-402 valve clearance adjustmentZMZ-402 valve clearance adjustment

Set the piston of the first cylinder to TDC. To do this, rotate the crankshaft so that the third mark on the pulley is aligned with the boss on the cover of the timing sprockets.

After that, remove the distributor cap and check that the slider is in the contact position of the 1st cylinder.

If not, rotate the crankshaft one revolution. Both valves of the first cylinder must be closed.

ZMZ-402 valve clearance adjustment

With a 14 key, we release the lock nut of the adjusting screw and unscrew the adjusting screw by one or two turns.

Insert a feeler gauge between the valve stem and rocker arm. We wrap the adjusting screw until the probe moves in the gap with little effort.

High having set the gap, hold the adjusting screw and tighten the lock nut and check the gap again. We adjust the clearances of both valves of the first cylinder.

ZMZ-402 valve clearance adjustment

Then with a special key behind the ratchet:

Turn the crankshaft half a turn (180°) and adjust the clearances in the valve drive of the 2nd cylinder.

Turn the crankshaft another half turn (180°) and adjust the clearances in the valve drive of the 4th cylinder.

Turn the crankshaft another half turn (180°) and adjust the clearances in the valve drive of the 3rd cylinder.

The value of the gaps in the valve drive:

Number

cylinder

Valve

Value

gap,

mm

1

Inlet

Graduation

0.40 - 0.45

0.35 - 0.40

2

Inlet

Graduation

0.40 - 0.45

0.40 - 0.45

3

Inlet

Graduation

0.40 - 0.45

0.40 - 0.45

4

Inlet

Graduation

0.40 - 0.45

0.35 - 0.40

After adjusting the valves, you need to start the engine and after warming up, make a test drive.

Check engine operation in all modes. In case of unsatisfactory operation of the valve mechanism, repeat the clearance check.