Instruction. When repairing engines with leaking valves, it is not enough to simply modify or replace valve seats and valves. Valve guides need to be checked for wear, especially on long life engines. Valve seats should only be reworked enough to achieve a perfect seating band. Before reworking, the maximum allowable reworking allowance should be calculated. If the allowance is exceeded, but the refinement may be impaired, the function of hydraulic clearance control in the valve drive (hydraulic compensators), which will entail the replacement of the cylinder head.
Calculation of the maximum allowable allowance for revision
Insert the valve and press firmly against the seat. If the valve is replaced during repair, the new valve should be used for measurements.
Measure the distance -a- between the end face of the valve and the upper surface of the cylinder head with a depth gauge. Based on the measured distance and the minimum size, calculate the maximum allowable rework allowance. Minimum size for inlet valve: 43.4 mm. Minimum size for exhaust valve: 43.2 mm. Measured distance minus minimum dimension = maximum allowable rework allowance.
Inlet valve example
- Measured distance: 44.1mm
- Minimum size: 43.4mm
- Maximum allowable reworking allowance = 0.7 mm
Instruction. If the maximum allowable reworking allowance is 0 mm or less than 0 mm, repeat the measurement with a new valve. If the result is still 0 mm or less than 0 mm, the cylinder head should be replaced.
Inlet valve modification
a. 35.7mm
b. 1.6mm
45°- Valve seat bevel angle
30°- Upper correction angle
Instruction. Calculate the maximum allowable rework allowance — The symbol that determines the position of the illustration. A valve seat chamfer of 30°is absolutely necessary for flow conditions in the inlet.
Finalization of the exhaust valve seat
a. 31.4 mm
b. 2.7mm
45°- Valve seat bevel angle
30°- Upper correction angle
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