NOTE: When repairing engines with leaky valves, treat or replace the valve seats and valves insufficiently. Especially in engines with a long service life, it is necessary to check the valve guides for wear.
Valve seats should be reworked only to the extent that a flawless appearance of the working surface is achieved. The maximum allowable machining allowance should be calculated before machining. If the machining allowance is exceeded, the hydraulic clearance adjustment function in the valve drive may be impaired (hydraulic compensators), which will entail replacing the cylinder head.
Remove the camshafts.
Calculate the maximum allowance for machining as follows:
- insert the valve into the guide and press it firmly against the seat;
NOTE: If the valve is replaced during repair, use a new valve for measurements.
- measure the distance A between the end of the valve stem and the top edge of the cylinder head (Fig. 2.85);
- calculate the maximum allowable machining allowance based on the measured distance A and the minimum allowable dimension.
Minimum dimensions
| short intake valve, mm | 31,8 |
| long inlet valve, mm | 10,2 |
| short exhaust valve, mm | 31,8 |
| long exhaust valve, mm | 10,2 |
Measured distance A minus minimum dimension = max. allowable rework dimension.
Example:
- Measured distance 10.6 mm
- Minimum size 10.2 mm
- Maximum allowance for processing 10.6-10.2=0.4 mm
NOTE: In the following diagrams, the maximum allowance for machining valve seats is shown as dimension B.
Intake valve seat machining
a - 30.6 mm
b - maximum allowable finishing size
c - 0.9-1.5 mm
d - max 35.0 mm
r2 - radius 2.0 mm
Z - lower edge of the cylinder head
a - 45° valve seat chamfer angle
b - 30° angle of the upper correction chamfer
g - 60° angle of the lower correction chamfer
Exhaust valve seat machining
a - 26, mm
b - maximum allowable finishing size
c - 1.2-1.7 mm d - max 29.0 mm
r2 - radius 2.0 mm
Z - lower edge of the cylinder head
a - 45° valve seat chamfer angle
b - 30° angle of the upper correction chamfer
g - 60° angle of the lower correction chamfer
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