Skoda Workshop Service and Repair Manuals

Reworking 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. t  Rework valve seats only sufficiently in order to obtain a proper contact pattern. Calculate the maximum permissible reworking dimension before commencing. If the reworking dimension is exceeded, proper operation of the valve gear is no longer assured and the cylinder head must be replaced. Calculating maximum 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 and the seat surface for valve spring. –  Calculate max. permissible reworking dimension from the distance measured and the maximum dimension.

Maximum dimensions in mm	1.0 ltr. engine	1.4 ltr. engine
Inlet valve	43,1	42,7
Exhaust valve	43,0	42,8

Maximum dimension less distance measured = max. permissible reworking dimension. Example:

	Maximum dimension	43,1	mm
-	Measured distance	42,7	mm
=	max. permissible reworking dimension	0,4	mm

Note If the max. permissible reworking dimension is 0 mm, repeat measurement with a new valve. If the max. permissible reworking dimension is again 0 mm, replace cylinder head.

reworking valve seats

Dimension		Valve seats
1.0 ltr. engine:
Ø a	mm	Valve seat diameter:	33,4 ± 0.1 - inlet valve 26.4 ± 0.1 - exhaust valve
1.4 ltr. engine:
Ø a	mm	Valve seat diameter:	32.9 -0.1 - inlet valve 29.6 -0.1 - exhaust valve
b	mm	max. permissible reworking dimension
1.0 ltr. engine:
c	mm	Valve seat width:	1.3 up to 1.6 - inlet and exhaust valve
1.4 ltr. engine:
c	mm	Valve seat width:	1,45 up to 1,75 - inlet valve 1,65 up to 1,95 - exhaust valve
Z		Bottom edge of cylinder head
45°		Valve seat angle
30°		Top correction angle
60°		Bottom correction angle

Work procedure Reworking can be carried out with a machine or by hand. The following conditions must be met: 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).

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	7,0 -0,01
Exhaust valve

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

Valve seat		Ø Milling cutter 90 mm	Ø Milling cutter 120 mm	Ø Milling cutter 60 mm
Inlet valve	1.0 ltr. engine	36	38	21/34
	1.4 ltr. engine	36	38	21/34
Exhaust valve	1.0 ltr. engine	30	30	max. 30 → Note
	1.4 ltr. engine	32	32	21/34

1)  May not yet be contained in NAC milling cutter kit.

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

–  Grind in valve/valve seat with fine grinding paste so as to achieve a perfect contact pattern -arrows-. –  Inspect valve for tightness. The inspection can be carried out with water colour (perfect contact pattern over entire circumference) or by filling fuel into the combustion chamber (no fuel must flow out at the valve seat).   Note After installing the cylinder head, carry out basic setting of the hydraulic valve clearance compensation → Chapter.