Mitsubishi FUSO FH 1997, Service Manual

Page: 170 / 200

11-21
11
78OP
Valve and valve seat
[Inspection]
• Apply red lead evenly to entire surface A of valve seats 19, 20 that
contact valves 7, 8.
• Fit valves 7, 8 to valve seats 19, 20 and tap once without rotating.
NOTE
Be sure to carry out inspection under the condition that valves 7,
8 and all parts of valve guides 17, 18 are normal.
01968
A
0
01969
• Check how much red lead has transferred to valves 7, 8 to determine
the contact of the valve and the seat. According to the degree of
abnormality, take proper measures to correct it.
01970
B
A
[Correction]
Valve polishing is done in the following manner:
• Apply valve lapping compound thinly to contact surface A of valves
7,8 with valve seats 19, 20.
CAUTION
–
Take care not to smear stems B of valves 7, 8 with the compound.
NOTE
• Start with medium grit compound (120 to 150 grit) and for finish-
ing up, use finer grit (200 grit or finer).
• Mixing with a small amount of engine oil will make the compound
consistent and make even application easier.
7, 8
01971
• Tap valves 7, 8 against valve seats 19, 20 several times while rotating
the valves slightly at each strike.
• Clean off the compound with gas oil.
• Apply engine oil to contact surface A of valve seats 19, 20 and smooth
the surface.
• Check the contact of valves 7, 8 and valve seats 19, 20.
• If contact does not take place completely around the seat, replace
valve seats 19, 20.
0
Contact conditions Correction measures
Minor fault Valve lapping
Major fault Repair of valve and seat or replacement of both