Valve Seat: Service and Repair

Valve Seat, Refacing

Special tools, testers and auxiliary items required

• Depth Gauge

• Valve Seat Refacing Tool

Procedure

• When repairing engines with leaking valves, it is not sufficient to rework or replace valve seats and valves. It is also necessary to check the valve guides for wear. This is particularly important on high mileage engines. Refer to => [ Valve Guide, Checking ] Testing and Inspection.

• Only reface valve seats enough until a perfect contact pattern is obtained. The maximum permissible refacing dimension must be calculated before the work is carried out. If the refacing dimension is exceeded, the function of the hydraulic lifters can no longer be guaranteed and therefore the cylinder head should be replaced.

- Remove the camshafts. Refer to => [ Camshafts ] Service and Repair.

Maximum Permitted Refacing Dimension is Calculated as Follows:

- Install the valve and press it firmly against the seat.

• If the valve is to be replaced as part of a repair, use a new valve for the calculation.

- Measure the distance - a - between the end of the valve stem and the upper edge of the cylinder head.






- Calculate max. permissible reworking dimension from measured distance - a - and minimum dimension.

Minimum Dimensions






Measured distance - a - minus minimum dimension = Max. permissible refaced dimension.

Example:






Refacing Intake Valve Seat






a = Diameter 32.8 mm

b = Max. permissible reworking dimension*

c = 0.9 to 1.5 mm

d = Max. diameter 38.0 mm

r2 = Radius 2.0 mm

Z = Cylinder head lower edge

alpha = 45° valve seat angle

beta = 30° upper correction angle

gamma = 60° lower correction angle



Refacing Exhaust Valve Seat






a = Diameter 29.8 mm

b = Max. permissible refacing dimension*

c = 1.2 to 1.7 mm

d = Max. diameter 35.0 mm

r2 = Radius 2.0 mm

Z = Cylinder head lower edge

alpha = 45° valve seat angle

beta = 30° upper correction angle

gamma = 60° lower correction angle