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Camshaft seals: replacing > < Valve control: Repairing

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Valve seats: re-cutting
Valve seats: re-cutting
Special tools and workshop equipment required
t  Depth gauge
t  Valve seat re-cutter
  Note!
t  When repairing engines with leaky valves, it is not enough to re-cut the valve seats, seat the valves or replace both. Especially for engines with high mileage, it is important to check for wear in the valve guides → Chapter.
t  Re-cut the valve seats just to the point where a perfect contact is achieved. Before re-cutting, the maximum allowable re-cut dimension must be calculated. If the re-cut dimension is surpassed, the hydraulic compensation function of the valve play will not be ensured, and the cylinder head must be replaced.
Calculate the maximum admissible re-cutting dimension
–  Introduce the valve and press it hard against the seat.
  Note!
If the valve is replaced during the reparation, use the new valve for the measurement.
   
–  Measure the distance -a- between the end of the stem and the upper edge of the cylinder head.
–  Calculate the maximum admissible re-cutting dimension starting with the measured distance and the minimum dimension.
Minimum dimensions:
Intake valve 7.6 mm
Exhaust valve 7.6 mm
Distance measured less the minimum dimension = maximum admissible re-cutting dimension.
Example:
  N15-0079
 Distance measured8,0 mm
-Minimum dimension7,6 mm
=Maximum admissible re-cutting dimension → Note0,4 mm

1)  The maximum admissible re-cutting dimension is shown in the illustrations as dimension “b”.
   
Intake valve seat: re-cutting
  N15-0096
a=Ø 28,7 mm
b=maximum admissible re-cutting dimension → Note
c=1,5…1,8 mm
Z=lower edge of the valve
α=45° valve seat angle
β=30° upper correction angle
γ=60° lower correction angle

2)  Calculation of the maximum admissible re-cutting dimension → Anchor.
Exhaust valve seat: re-cutting
   
a=Ø 25,0 mm
b=maximum admissible re-cutting dimension → Note
c=approx 1.8 mm
Z=lower edge of the valve
α=45° valve seat angle
β=30° upper correction angle
γ=60° lower correction angle

3)  Calculation of the maximum admissible re-cutting dimension → Anchor.
   

Camshaft seals: replacing > < Valve control: Repairing