Instruction. If grinding does not achieve a perfect seating surface of the valve seats, the seats must be machined. When repairing engines with leaking valves, it is not enough to process or replace the cylinder seats and valves. Especially in engines with a long service life, the valve guides must be checked for wear. Valve seats should only be machined until a flawless seating surface is achieved. Before refining, it is necessary to calculate the maximum allowable rework size. If the processing tolerance is exceeded, the hydraulic control function may be impaired (gap in the drive of hydraulic compensator valves) will entail the replacement of the cylinder head.
A. Calculation of the maximum allowable rework tolerance
Insert the valve into the guide and press it firmly against the seat. If the valve is replaced during repair, the new valve should be used for measurements. Depth gauge -VAS 6082- measure the distance between the end of the valve stem (upper edge) and the top surface of the cylinder head. Calculate the maximum allowable rework allowance based on the measured distance and the minimum allowable size. Minimum size for intake and exhaust valves: 7.6 mm. measured distance. minimum size = maximum allowable rework allowance.
Example: measured distance. 8.0 mm, minimum dimension 7.6 mm, maximum allowable machining allowance = 0.4 mm.
Instruction. If the maximum allowable machining allowance is 0 mm or less than 0 mm, repeat the measurement with a new valve. If the measured result is always 0 mm or less than 0 mm, replace the cylinder head.
B. Valve seat rework
Inlet valve seat:
- A. ∅ 28.7 mm,
- b. the maximum allowable allowance for revision c. 1.5...1.8 mm,
- z. bottom edge of cylinder head
- a. 45°valve seat bevel angle,
- β. 30°top corrective chamfer angle,
- γ. 60°angle of bottom corrective chamfer/
Exhaust valve seat
- A. ∅ 25.0 mm,
- b. the maximum allowable allowance for revision, s. approx. 1.8 mm
- z. bottom edge of cylinder head
- a. 45°valve seat bevel angle,
- β. 30°top corrective chamfer angle,
- γ. 60°bottom corrective chamfer angle.
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