Skoda Workshop Service and Repair Manuals

Reworking valve seats   Note If no perfect contact pattern is achieved by grinding in the valve seats, rework the valve seats. Special tools and workshop equipment required t  Depth gauge/caliper gauge t  NAC milling cutter for reworking valve seats t  Grinding paste   Note t  When carrying out repairs on engines with leaking valves, it is not sufficient to machine or replace the valve seats and valves. It is also necessary to inspect the valve guides for wear, particularly on engines with a high mileage → Chapter. t  Rework valve seats only sufficiently in order to obtain a proper contact pattern. t  Calculate the maximum permissible reworking dimension before commencing. t  If the reworking dimension is exceeded, proper operation of the hydraulic valve clearance compensation is no longer assured and the cylinder head must be replaced.

Calculating max. permissible reworking dimension –  Insert valve and press firmly against the valve seat.   Note If the valve is replaced when carrying out repair work, use a new valve for the measurement. –  Measure distance -a- between the valve stem ends (upper edge) and the upper cylinder head surface with depth gauge. –  Calculate max. permissible reworking dimension from the distance measured and the minimum dimension. l  Minimum dimension for inlet and exhaust valve: 31.7 mm. Measured distance less minimum dimension = max. permissible reworking dimension.

Example for inlet valve:
	measured distance -a-		32.0 mm
-	Minimum dimension		- 31.7 mm
=	max. permissible reworking dimension		= 0.3 mm

Note If the max. permissible reworking dimension is 0 mm or less than 0 mm, repeat measurement with a new valve. If the measuring result is still 0 mm or less than 0 mm, replace cylinder head.

Reworking inlet valve seat

Dimension		Inlet valve seat
Ø a	mm	39,2
b	mm	max. permissible reworking dimension
c	mm	1,8 … 2,2
Z		Bottom edge of cylinder head
α		45° valve seat angle
β		30° top correction angle
γ		60° bottom correction angle
S		Combustion chamber surface area

Reworking exhaust valve seat

Dimension		Exhaust valve seat
Ø a	mm	32.4 mm
b	mm	max. permissible reworking dimension
c	mm	2.2 … 2.6 mm
Z		Bottom edge of cylinder head
α		45° valve seat angle
β		30° top correction angle
S		Combustion chamber surface area

Note The exhaust valve seat rings are additionally provided with a restriction. During rework ensure that the radius of the restriction is not damaged. Work procedure Reworking can be carried out by hand while complying with the following conditions: l  Wear limit of valve guides must not exceed the permissible dimension → Chapter. l  Use NAC milling cutter with carbide metal tips (min. 90 HRC). l  Mill with the milling cutter using slight pressure in such a way that an even removal of swarfs is ensured over the whole working surface.

Reworking valve seats with NAC milling cutter –  Place cylinder head on a felt base and secure to prevent it from turning. –  Match diameter of guide drift to diameter of valve guide.

Valve guide	Ø Guide drift in mm
Inlet valve	6,0 -0,01
Exhaust valve

–  Match diameter of milling cutter to diameter of valve seat.

Milling sequence 1 -  Mill valve seat with 90° milling cutter until a perfect contact pattern is achieved. (Do not exceed maximum permissible reworking dimension!) 2 -  Chamfer top correction angle with 120° milling cutter until the valve seat diameter -a- ( → Anchor) is achieved. 3 -  Mill bottom correction angle with 60° milling cutter until valve seat width -c- ( → Anchor) is achieved. pay attention to the notes → Anchor.

–  Grind in valve/valve seat with fine grinding paste so as to achieve a perfect contact pattern -arrows-. –  Check contact pattern e.g. with water colour (perfect contact pattern over entire circumference). –  Install valve springs. –  Inspect valve for tightness. The tightness of the valves can be checked by filling petrol into the inlet and outlet canal (no petrol must flow out at the valve seat). After the repair measure the dimension -a- again and calculate the maximum permissible reworking dimension → Anchor.   Note If the reworking dimension is exceeded, proper operation of the valve gear is no longer assured and the cylinder head must be replaced.