A8L V8-4.2L (BFM) (2004)
Valve Seat: Service and Repair
Valve Seat, Refacing
‹› If a perfect contact pattern is not achieved by refacing the valve seats, replace the cylinder head.
Special tools, testers and auxiliary items required
‹› Depth gauge
‹› Valve seat refacing tool
‹› When repairing engines with leaking valves, it is not sufficient to reface the valve seats/valves or replace the valves. It is particularly important to
check the valve guides for wear on engines with higher mileage performance. Refer to => [ Valve Guides, Checking ] See: Valve Guide/Testing
and Inspection.
‹› Only reface the valve seats enough until a perfect contact pattern is obtained.
‹› Before refacing, determine the maximum refacing dimension.
‹› If the refacing dimension is exceeded, the function of the hydraulic lifters can no longer be guaranteed and therefore the cylinder head should be
replaced.
Determining Maximum Allowable Refacing Dimension
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Insert the valve and press it firmly against the valve seat.
‹› If the valve is to be replaced as part of a repair, use the new valve for the calculation.
-
Measure the distance - a - between the end of the valve stem and the camshaft center axle (camshaft center axle is located at the level of the
cylinder head upper edge).
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Determine the maximum allowable refacing dimension using the distance measured and minimum dimension.