Mitsubishi 6M70 Workshop Manual page 60

CYLINDER HEAD AND VALVE MECHANISM
11-50
Lapping valve
• Lap the valve in the following sequence.
• Apply a thin coat of lapping compound to the contact surface of
the valve seat. Adding a small amount of engine oil to the lap-
ping compound can facilitate even application.
• Start with an intermediate-grit compound (120 to 150 grit) and
finish with a fine-grit compound (200 grit or more).
CAUTION
• Do not put any compound on the stem.
• Strike the valve several times against the valve seat while rotat-
ing the valve a little at a time.
• Wash away the compound with diesel fuel.
• Apply engine oil to the contact surface of the valve seat and rub
in the valve and seat well.
• Inspect the contact pattern between valve and valve seat again.
• If the contact pattern is still defective, replace the valve seat.
Inspection: Mitsubishi 6M70 Valve seats
• If the valve seat is refaced or replaced after performing the fol-
lowing inspection, make sure to lap the valve and valve seat.
(1) Valve seat width
• If the measurement exceeds the limit, reface or replace the
valve seat.
(2) Valve sinkage from cylinder head bottom surface
• Perform measurement keeping the valve in close contact with
the valve seat.
• If the measurement exceeds the limit, reface or replace the de-
fective part(s).
Refacing the valve seat
• Grind the valve seat using a valve seat cutter or valve seat
grinder.
• Place a piece of sandpaper of approximately #400 between the
cutter and valve seat and grind the valve seat lightly.
• Use a 15° or 75° cutter to cut the valve seat width within the
standard range. Replace the valve seat if it cannot be refaced
within the standard range.
CAUTION
• Make sure that the valve seat refacing does not cause the
valve sinkage to exceed the limit.