Allroad Quattro V8-4.2L (BAS) (2004)
Valve Seat: Testing and Inspection
Valve seats, reworking
Note: Rework valve seats if grinding-in does not yield proper surface appearance.
Special tools and equipment
^
Depth gauge
^
Valve seat machining device
Note:
^
When servicing engines where valves are leaking, it is not sufficient to machine/replace valve seats and valves. Particularly in the case of
high-mileage engines, it is necessary to check the valve guides for wear.
^
Valve seats are only to be reworked to the extent required to yield a proper surface appearance.
^
The maximum permissible reworking dimension is to be calculated before starting work.
^
If reworking dimension is exceeded, proper hydraulic valve filter operation can no longer be guaranteed and cylinder head is to be replaced.
Calculating max. perm. reworking dimension
-
Insert valve and press it firmly against valve seat.
Note: Use new valve for measurement purposes if the valve is replaced as part of repair work.
-
Measure distance -a- between end of valve stem and center axis of camshaft (center axis of camshaft is on a level with top edge of cylinder head).
-
Calculate maximum permissible reworking dimension from distance measured and minimum dimension.
Minimum dimensions
Measured distance minus minimum dimension max. perm. reworking dimension
Note: If maximum permissible reworking dimension is 0 mm or less than 0 mm, repeat measurement with new valve. Replace cylinder head if result
obtained is still 0 mm or less than 0 mm.