Engine body
Replacement of valve seat
Fig. 17. A = distance between cylinder head plane and
valves.
The valve seat should be replaced when the distance
"A" in Fig. 17 measured with a
new
valve exceeds
1.8 mm (.0708").
1.
Remove the old valve seat by heating it up with a
gas jet (600-700°C / 1112-1292°F) diagonally
over the seat.
Allow the cylinder head to cool approx. 3-5 minu-
tes in the air. Carefully tap out the seat with
mandrel (check that the cylinder head is not dama-
ged).
Alternatively the valve seat can be milled out
(check that the cylinder head is not damaged).
2.
Clean the seat housing in the cylinder head care-
fully.
Check the head for cracking.
3.
Cool down the new seat with liquid nitrogen or the
li
ke to minus 60-70°C (140-158°F) and heat up the
cylinder head to approx. 60-100°C (140-212°F).
4.
Press the seat in the head. Use a hydraulic press
(1000-1500 kp / 2204-3307 lbf) and suitable
mandrel.
5.
Work the seats to the correct angle and width.
2 8
Grinding of valves and valve seats
1.
Use a valve spring tensioner and dismantle
the
valve lock. Remove the valve spring washers,
springs and aloes. Place the parts in the correct
order in a valve rack. Remove the valve stem seals.
2.
Clean the parts.
Fig. 18. Checking of valve spindle wear
Check the wear on the valve spindle. Measure the
diameter with a micrometer at points I, II and III as
per Fig. 18.
'
Fig. 19. Valve disc edge
4.
Grind the valves in a valve grinding machine
Grind the sealing surface as little as possible, just
so that it is "clean". If the the valve disc edge after
grinding is less than 0.5 mm (.019 in) the valve
should be scrapped (see Fig. 19). The same ap-
plies to valves with crooked valve spindles.
Diameter mm:
I
nlet
Outlet
MD2010, MD2020
5.90 mm 5.90 mm
(.2322 in)
(.2322 in)
MD2030, MD2040
6.89 mm 6.84 mm
(.2712 in)
(.2692 in)
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