32
Group 21 Short block
4. Grind the valves in a valve grinding machine.
Grind the sealing surface as little as possible, just
enough to “clean” it up. If the edge of the valve
head (B) after grinding is less than 0.5 mm, the
valve must be scrapped. Equally, any valve with
a bent valve stem must be scrapped.
5. Check the wear of the valve guides (refer to
“Check of valve guides”) before machining the
valve seats.
6. Mill the valve seats. When machined, only re-
move enough material to give the valve seat the
correct shape and a good mating surface.
Note. Do not grind so much that the valve depth ex-
ceeds the permissible value. Please refer to “Chang-
ing the valve seats”.
New valve seats shall be milled down so far that
the distance between the cylinder head plane and
the valve head surface (A) is 0.65-0.95 mm
7. Grind the valves in with grinding paste, and check
contact with marker dye.
8. Install the seals, valves, valve springs, spring
washers, valve cotters and valve caps. Refer to
“Assembly of cylinder head”.
Checking the valve guides*
Special tools: 999 9683, 999 9696
1 Put the cylinder head on the bench, and put
valves in the valve guides.
2 Measure the wear with rocker indicator 999 9683
and magnetic stand 999 9696.
Lift each valve about 2 mm from its seat, put the
measurement tip on the edge of the valve head
and check the wear.
Permissible clearance between valve and valve
guide:
Inlet valve, max clearance 0.20 mm
Exhaust valve, max clearance 0.25mm
* Note. Since the valve guides are machined directly in the
cylinder head, the cylinder head must be changed when the
clearance is too great, even when the valve is new.
A
B
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