Kohler KD 425-2 Workshop Manual page 20

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CHECKS AND OVERHAUL
12
13
14
15
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After prolonged running of the engine the hammering of the valves on
their seats at high temperature tends to harden the faces of the se-
ats and makes manual grinding difficult. It is necessary to remove the
hardened surface with a 45° cutter (fig. 12).
Grinding of valve seats causes a widening of the valve seat face P
(fig.13).
Final lapping of the valve on the seat must be carried out by coating
the seat with a fine lapping compound and rotating the valve in a
clockwise and counterclockwise direction with slight pressure until a
perfect surface finish is obtained (fig.14).
Observe the valve seating clearances indicated in the following table
(fig.10).
Fitting mm
d= 0,8 ÷1,0
In the case of lower values the valve may strike the piston.
In the case of values in excess of 1.3 mm the valve seat
rings must be replaced.
Fitting of new seats or valves always requires preparatory grinding.
Valves are available with the external diameter increased by 0.5 mm.
After grinding wash the valve and seat carefully with petrol or paraffin
in order to remove residual grinding paste and chips. Once you have
finished grinding check the efficiency of the seal between the valve
and seat as outlined below:
1. Fit the valve on the head with spring, washers and split cones
(fig.9).
2. Invert the head and pour in a few drops of diesel fuel or oil
around the edges of the valve head.
3. Blow compressed air into the inlet of the cylinder head taking
care to seal the edges so that the air does not escape (fig.15).
Should air bubbles form between the seat and the valve remove the
valve and regrind the seat.
KD 425-2 Workshop Manual_cod. ED0053029360_1° ed_ rev. 00
Max. wear mm
d=1,3