They are driven by the cams of the intake and exhaust overhead camshafts through cylindrical hydraulic tappets. The engine valve parameters are given in the table. 3.4. The minimum height of the cylindrical part of the valve plate must be at least 0.5 mm.
Table 3.4. Engine valve parameters
| Valve parameters | Engine model | ||
| M54B22 | M54B25 | M54B30 | |
| Intake valves | |||
| Plate diameter, mm | 30,0 | 33,0 | 33,0 |
| Landing diameter, mm | 29.4 | 32,4 | 32,4 |
| Tolerance for head diameter, mm | from 0.00 to -0.016 | ||
| Rod diameter, mm nominal | 6,00 | ||
| 1st repair | 6,10 | ||
| 2nd repair | 6,20 | ||
| approval of use. | from -0.025 to -0.040 | ||
| Clearance between valve guides and valve stems, mm* | 0.5 | ||
| Exhaust valves | |||
| Plate diameter, mm | 27,00 | 30,5 | 30,5 |
| Landing diameter, mm | 26,50 | 30,0 | 30,0 |
| Tolerance for head diameter, mm | from 0.00 to -0.016 | ||
| Rod diameter, mm | |||
nominal | 6,00 | ||
1st repair | 6,10 | ||
2nd repair | 6,20 | ||
admission | from -0.040 to -0.055 | ||
| Clearance between valve guides and valve stems, mm* | 0,5 | ||
* The measurement technique is shown in Fig. 3.7.
One of the main indicators of engine wear depends on the condition of the valve mechanism - the compression value in its cylinders, which is checked with a special device - a compression gauge installed in the spark plug hole. The rules for its installation and removal, measurements are given in the instructions for the device and described below. The device reading for a new engine is 10-12 bar (kgf / cm²), with extreme wear - 8.0 bar.
The difference in pressure between the cylinders of one engine should not exceed 1.5 bar. If the difference is more than 1.5 bar or the pressure is less than 8.0 bar, this indicates increased wear of the piston rings, cylinder mirrors, and valves. Such an engine is subject to removal and repair.
Valve springs
Valve springs are designed to ensure a tight fit of the valves on the seats. Each intake and exhaust valve has a spring, which is identical for both intake and exhaust valves. The spring is installed with the top of the cone towards the crackers.
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