Audi Workshop Service and Repair Manuals

Machining valve seats Special tools and workshop equipment required t  Depth gauge t  Valve seat machining tool   Note t  If a good seating pattern cannot be obtained by grinding the valve seats (lapping), they must be refaced (machined): 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  Calculate the maximum permissible machining dimension before machining. t  If the machining dimension is exceeded, the function of the hydraulic valve play compensation can no longer be guaranteed 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. –  Measure distance -a- between valve stem end (upper edge) and upper cylinder head surface with a depth gauge. –  Calculate the maximum permissible machining dimension using the measured distance and the minimum dimension. l  Minimum dimension for inlet valve and exhaust valve: 31.2 mm. Measured distance minus minimum dimension = max. permissible machining dimension.

Example for inlet valve:
	Measured gap -a-		31.5 mm
-	Minimum dimension		- 31.2 mm
=	max. permissible machining dimension		= 0.3 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 measured result is again 0 mm or less than 0 mm, renew the cylinder head.

Machining inlet valve seat

Inlet valve seat
a	=	Ø 39.2 mm
b	=	max. permissible machining dimension
c	=	1.8 … 2.2 mm
Z	=	Bottom surface of cylinder head
45°	=	Valve seat angle
30°	=	Correction angle (top)

Note Calculating maximum permissible machining dimension → Anchor.

Machining exhaust valve seat

Exhaust valve seat
a	=	Ø 32.4 mm
b	=	max. permissible machining dimension
c	=	2.2 … 2.6 mm
Z	=	Bottom surface of cylinder head
45°	=	Valve seat angle
30°	=	Correction angle (top)

Note t  Calculating maximum permissible machining dimension → Anchor. t  Exhaust valve seat inserts also have an additional constriction. When machining, it is essential to ensure that the radius of the constriction is not damaged.