General information
To compensate for thermal expansion of the valves, a gap is provided in the valve mechanism, which must be set correctly. If the gap is too small, the valve timing changes. Late closing and early opening of the valves leads to a loss of engine power and uneven operation. In extreme situations, the valves can become deformed from impacts with the pistons, and the valve seats can burn. If the gap is too large, the valves open late and close early, i.e. the valve timing changes, engine power decreases, and the engine runs unevenly. Valve installation is considered correct when they are perfectly sealed, have an acceptable gap, and do not knock in the guide bushings.
The valve clearance can be checked and adjusted both on a cold and warm engine.
Checking and adjusting
1. Remove the cylinder head cover (see illustration). Unscrew the oil screen (see illustration).
2. Set the gearbox to neutral position, apply the handbrake.
3. Turn the engine by the central bolt of the crankshaft pulley in the direction of normal engine rotation. This will also turn the camshaft.
4. Set the piston of the 1st cylinder to TDC. To do this, turn the crankshaft until the valves of the 1st cylinder overlap. "Overlapping" the valves means that while the camshaft cam that controls the position of the intake valve begins to release the valve mechanism lever, the cam that controls the exhaust valve begins to press the lever to open the valve. The valves are overlapped if both cams are facing down and the bisector of the angle between the cam apexes is vertical. At this time, the mark on the camshaft gear coincides with the mark on the housing (see illustration).
5. In this position, check the clearances of the following valves: exhaust and intake valves of the 4th cylinder, intake valve of the 3rd cylinder, exhaust valve of the 2nd cylinder (see illustration).
6. To check the valve clearance, insert the feeler gauge into the gap between the lever and the camshaft cam, while the feeler gauge should be slightly "clamped".
7. Valve clearance: for the inlet valve - 0.2 mm, for the outlet valve - 0.3 mm.
8. Turn the crankshaft 1 full revolution in the direction of normal rotation, the valves of the 4th cylinder should be closed. The mark on the camshaft gear will turn 180° and will be facing up (see illustration). The TDC mark on the flywheel is now again opposite the indicator on the clutch box.
9. Measure the clearances of the following valves: exhaust and intake valves of cylinder 1, intake valve of cylinder 2, exhaust valve of cylinder 3.
10. If the valve clearances do not correspond to the permissible value, rotate the bolt of the corresponding lever using a special key (see illustration).
11. Install the oil screen, tighten the bolts with a tightening torque of 10 Nm.
12. Place the new cylinder head cover gasket, carefully and evenly tighten the cover screws.
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