- 19 -
KD 477-2 Workshop Manual_cod. ED0053029370_
1° ed
_ rev.
00
X
9
10
11
12
0,7 ÷ 1,2
2
0,9 ÷ 1,1
1,8
Fitting mm
Max. wear mm
Fitting mm
Max. wear mm
Cutting of the valve seats involves the widening of the valve seat face
P
with a consequent reduction of seal of the valve itself, fig. 9
If face
P
is more than
2 mm
wide, invert cutter and lower level
Q
of
the seat, fig. 10, so as to restore the
P
level to the value of:
Final lapping of the valve on the seat must be carried out by coating
the seat with a fire grinding paste and rotating the valve backwards
and forwards with a slight pressure until a perfect finish to the surface
is obtained (fig. 11).
Make sure the face of the valve head in relation to the face of the
cylinder head is:
If the distance is less, the valve will strike the piston.
If the distance is more than
1.8 mm
the valve seat rings
need to be changed. Fitting of new valves or seats always
requires grinding.
After grinding, wash valve and seat carefully with petrol or paraffin to
eliminate any residual grinding paste or cuttings.
To check the worthiness of the seal between valve and seat, after
grinding has taken place, proceed as follows:
1
. Fit valve on head with spring, plates and cotters (see fig. 5).
2
. Invert head and pour a few drops of diesel or oil round the out-
side 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. 12).
Should air bubbles form between the seat and the valve, remove the
valve and regrind the seat.
The fit can also be checked by pushing the valve upwards and letting
it fall freely down onto its seat. If the resulting bounce is considera-
ble and uniform, also when the valve is rotated, it means that the fit
is good. If not, continue grinding until the conditions described above
are achieved.
CHECKS AND OVERHAUL
Valve seats with an external diameter increased by
0.2 mm
, are avai-
lable.
