S4 V8-4.2L (BHF) (2004)
Valve Seat: Service and Repair
Valve seats, refacing
Note: If a perfect contact pattern is not created after hand-lapping valve seats, reface valve seats.
Special tools, testers and auxiliary items required
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Depth gauge
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Valve Seat Refacing Tool
Note:
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When servicing engines with leaking valves, refacing or replacing valve seats and valves is not sufficient. It is particularly important to check
valve guides for wear on engines with higher mileage Valve guides, checking
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Only reface valve seats enough until a perfect contact pattern is obtained.
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Before refacing, determine maximum refacing dimension.
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If refaced dimension is exceeded, hydraulic valve lifter function is no longer guaranteed and cylinder head must be replaced.
Determining maximum allowable refacing dimension
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Insert valve and press tightly against valve seat.
Note: If valve is to be replaced during repair, use the new valve for measurement.
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Measure distance - a - between end of valve stem and camshaft center axis (camshaft center axis is located at level of cylinder head upper edge).
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Calculate maximum permissible refacing dimension from measured distance and minimum dimension.
Measured distance minus minimum dimension = max. permissible refaced dimension.
Note: If the maximum allowed refaced dimension is 0 mm or less than 0 mm, repeat the measurement using a new valve. If the measurement result
is still 0 mm or less than 0 mm, replace the cylinder head.