Prolonged operation of the engine with incorrect clearances can lead to premature wear of valve train parts - burning of valves, wear of rocker arms, bearing surfaces of tappets and camshaft cams.

If knocking occurs in the valve mechanism, it is necessary to check and, if necessary, adjust the gaps between the valves and rocker arms, which should be within 0.25-0.3 mm (for intake and exhaust valves).

Adjustment of clearances in the valve mechanism is carried out on a cold engine with an adjusting screw with a locknut installed in the short arm of the rocker arm.

To adjust the clearance in the valve mechanism, you need to set the piston of the first cylinder to the top dead center (TDC) of the compression stroke.

In this case, the hole on the crankshaft pulley should be located under the "TDC" mark on the ignition timing indicator located on the maximum speed limiter sensor.

In this position, you need to adjust the clearance of the following valves;

  • - inlet and outlet first cylinder
  • - exhaust second cylinder
  • - inlet third
  • - graduation fourth
  • - graduation fifth
  • - inlet seventh
  • - inlet eighth

Remaining valve clearances must be adjusted after turning the crankshaft 360° (full turn).

Adjustment in the second way is done in the following order:

Setting the TDC of the first cylinder in the compression stroke

Set the piston of the first cylinder to the TDC of the compression stroke, using the installation gear pointer (Fig. 1)

ZIL-131 valve thermal clearance adjustment

To do this, turn the crankshaft until the mark on the shaft pulley aligns with the TDC mark on the pointer.

In this case, both valves, inlet and outlet, of the first cylinder will be closed, and between the valve stem and the pressure end of the rocker arm, the largest gap will form, which we measure with a feeler gauge and, if necessary, adjust.

To adjust the clearance, holding the adjusting screw with a screwdriver, loosen the lock nut with a wrench, then insert the feeler gauge between the valve stem and the pressure end of the rocker arm and turn the adjusting screw with a screwdriver, setting the required clearance. Then, leaving the probe in the gap, we fix the adjusting screw with a lock nut using a wrench and a screwdriver.

After adjustment, the clearance should be 0.25-0.30mm for the intake and exhaust valves, with the 0.25mm feeler gauge passing freely through the gap, and the 0.30mm feeler gauge not passing through.

To adjust the clearance in the valves of the remaining seven cylinders, turn the crankshaft with the handle one quarter of a turn (by 90 °) and carry out the adjustment according to the specified method.

The adjustment is carried out sequentially, according to the order of operation of the cylinders 1-5-4-2-6-3-7-8, which is shown by dotted lines with arrows.

In order to accurately rotate the crankshaft one quarter of a turn, put chalk marks on the crankshaft pulley, placing them at an angle of 90 ° with the piston of the first cylinder at TDC (compression stroke).