audi Workshop Repair Guides

Audi Workshop Service and Repair Manuals

ABOUT US
Checking valves > < Checking valve guides

A4 Mk1

Machining valve seats
Machining valve seats
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
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  Calculate the maximum permissible machining dimension before machining.
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.
–  Measure distance -a- between top end of valve stem and upper surface of cylinder head with a depth gauge.
–  Calculate max. permissible machining dimension from measured distance and minimum dimension.
l  Minimum dimension for inlet valve and exhaust valve: 31.2 mm.
Measured distance minus minimum dimension = max. permissible machining dimension.
  A15-0925
Example: 
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 result is again 0 mm or less than 0 mm, renew the cylinder head.
   
Machining inlet valve seat
a - Ø 39.2 mm
b - Maximum 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.
  A15-0412
Machining exhaust valve seat
a - Ø 32.4 mm
b - Maximum 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.
  V15-0657

Checking valves > < Checking valve guides