Audi Workshop Service and Repair Manuals

Machining valve seats   Note If a good seating pattern cannot be obtained by grinding the valve seats (lapping), they must be refaced (machined): Special tools and workshop equipment required

t  Depth gauge -VAS 6082- t  Valve seat machining tool   Note t  When servicing engines with leaking valves, it is not sufficient to machine (reface) the valve seats and renew the valves. The valve guides must also be checked for wear. This is particularly important on high-mileage engines → Chapter. t  Valve seats should only be machined to the extent required to give a proper seating pattern. t  The maximum permissible machining dimension must be calculated before starting work. t  If the machining dimension is exceeded, the function of the hydraulic valve clearance compensation can no longer be ensured and the cylinder head must be renewed.

Calculating maximum permissible machining dimension –  Insert valve and press firmly against valve seat.   Note If the valve has to be renewed as part of a repair, use a new valve for the measurement. –  Use depth gauge -VAS 6082- to measure distance -a- between end of valve stem (upper edge) and top surface of cylinder head. –  Calculate maximum permissible machining dimension from measured distance and minimum dimension.

Minimum dimensions
Inlet valves (outer)	Inlet valve (centre)	Exhaust valves
31.0 mm	32.2 mm	31.9 mm

Measured distance minus minimum dimension = max. permissible machining dimension.

Example for inlet valve (outer):
Measured distance		31.4 mm
Minimum dimension		– 31.0 mm
Maximum permissible machining dimension		= 0.4 mm

Note If the maximum permissible machining dimension is 0 mm or less than 0 mm, repeat the measurement with a new valve. If the result is again 0 mm or less than 0 mm, renew the cylinder head.

Machining inlet valve seat a -  Ø 26.2 mm b -  1.5 … 1.8 mm Z -  Bottom surface of cylinder head α -  45° valve seat angle β -  30° upper correction angle γ -  60° lower correction angle   Note Calculating maximum permissible machining dimension → Anchor.

Machining exhaust valve seat a -  Ø 29.0 mm b -  1.8 mm Z -  Bottom surface of cylinder head α -  45° valve seat angle β -  30° upper correction angle γ -  60° lower correction angle   Note Calculating maximum permissible machining dimension → Anchor.