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Checking valve guides > < Checking camshaft axial clearance

Polo Mk5

Reworking valve seats
Reworking valve seats
Special tools and workshop equipment required
t  Depth gauge
t  Valve seat refacing tool
  Note
t  When repairing engines with leaking valves, it is not sufficient to rework or renew valve seats and valves. Particularly on high mileage engines, it is necessary also to check valve guides for wear → Chapter.
t  Valve seats are only to be reworked to the extent required to yield a proper surface appearance. Before beginning to rework valve seats, calculate the maximum permissible reworking dimensions. If the reworking dimension is exceeded, the hydraulic valve clearance compensation can no longer be guaranteed and the cylinder head must be renewed.
The max. permissible reworking dimension is calculated as follows:
–  Insert valve and press firmly against seat.
  Note
If the valve is to be renewed as part of a repair, use a new valve for the calculation.
   
–  Measure distance -a- between end of valve stem and upper edge of cylinder head.
–  Calculate maximum permissible reworking dimension from measured distance and minimum dimension.
Minimum dimension: inlet valve 7.6 mm, exhaust valve 7.6 mm
Measured distance minus minimum dimension = max. permissible reworking dimension.
Example:
  N15-0079
 Measured distance
– Minimum dimension		8.0
7.6		mm
mm
 Max. permissible reworking dimension0.4mm

1)  The max. permissible reworking dimension is shown on illustrations for reworking valve seats as dimension „b“.
   
Reworking inlet valve seat
  N15-0096
a
b
c
Z
α
β
γ		= Ø 28.7 mm
= Max. permissible reworking dimension1
= 1.5…1.8 mm
= Cylinder head lower edge
= 45° valve seat angle
= 30° upper correction angle
= 60° lower correction angle

2)  Calculating max. permissible reworking dimension → Chapter.
Reworking exhaust valve seat
   
a
b
c
Z
α
β
γ		= Ø 25.0 mm
= max. permissible reworking dimension1
= approx.1.8 mm
= Cylinder head lower edge
= 45° valve seat angle
= 30° upper correction angle
= 60° lower correction angle

3)  Calculating max. permissible reworking dimension → Chapter.
   

Checking valve guides > < Checking camshaft axial clearance