A8L Quattro Sedan V8-4.2L (AKB) (2002)
Valve Seat: Testing and Inspection
Valve seats, refacing
Special tools and equipment:
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Depth gauge
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Valve lapping tool
Notes:
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Repairing engines with leaking valves, especially engines with high mileage must include measuring valve guides.
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Before refacing, calculate maximum permissible refacing dimension.
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If the maximum permissible refacing dimension is exceeded, the function of the hydraulic valve lifters can no longer be guaranteed and the
cylinder head must be replaced.
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Reface valve seats just enough to produce a good seating pattern.
Maximum permissible refacing dimension, calculating
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Install valve and press it firmly onto the valve seat.
Note: If you intend to replace the valve, use new valve for measurement.
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Install valve and press firmly against valve seat.
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Measure distance between end of valve stem and top surface of cylinder head.
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Calculate maximum permissible refacing dimension from measured distance and minimum dimension.
Minimum dimensions
The measured distance minus the minimum dimension equals the maximum permissible refacing dimension.
Example:
Outer intake valve
Measured dimension 34.4 mm (1.354 inch)
Minimum dimension - 34.0 mm (1.338 inch)
Maximum permissible refacing = 0.4 mm (0.0157 inch)
Note: If the measured distance is less than the minimum dimension, repeat the measurement with new valves or replace the cylinder head.