31
Group 21 Short block
Changing the valve seats
NOTE! On D2-75 only the inlet valve seat can be
changed. On D2-55 both the inlet and exhaust valve
seats can be changed.
The valve seat should be changed when the distance
“A” measured with a new valve exceeds 1.8 mm.
1. Remove the old valve seat by heating it with a gas
flame (600-700
o
C) diagonally across the seat.
Let the cylinder heat cool for 3-5 min in the air.
Then carefully tap the seat out with a mandrel
(check that the cylinder head is not damaged).
The valve seat can also be milled out (check that
the cylinder head is not damaged).
2. Carefully clean the valve seat bed in the cylinder
head. Check the cylinder head for cracks.
3. Cool the new seat with dry ice or similar to minus
60-70
o
C and heat the cylinder head to approx.
60-100
o
C.
4. Press the seats into the cylinder head. Use a hy-
draulic press and a suitable mandrel.
5. Machine the seats to the correct angle and width.
A
Grinding of valve and valve seats
Special tools: 885 023, 885 498
1. Use valve spring compressor 885 023 and pres-
sure foot 885 498 to remove the valve cotters.
Remove the valve washers, springs and valves.
Place the parts in the correct order in a valve
holder. Remove the valve stem seals.
2. Clean the components.
3. Check valve stem wear. Measure the diameter
with a micrometer at points I, II and III.
Diameter, min. inlet: 6.89 mm
Diameter, min. exhaust: 6.84 mm
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