Valve Seat Correction - Yanmar 3TNV Series Service Manual

4. Disassembly, Inspection and Reassembly of Engines

4.2.6 Valve seat correction

[NOTICE]
Always check the oil clearance between the valve and valve guide before correcting the valve seat.
If it exceeds the limit, replace the valve or valve guide first to make the clearance satisfy the standard.
After correction, wash the valve and the cylinder head sufficiently with diesel oil to remove all grinding
powder or compound.
1) If the seat surface is slightly roughened: perform
[A] and [B] below.
[A]: Lap the valve and seat with a mixture of
valve compound and engine oil.
[B]: Lap with engine oil only.
2) If the seat is heavily roughened but the width is
almost normal, correct with a seat grinder or seat
cutter first. Then perform lapping [A] and [B].
Seat cutter angle
3) If the seat is heavily roughened and the width is
much enlarged, grind the seat inner surface with
a seat grinder whose center angle is 40°, then
grind the seat outer surface with a grinder whose
center angle is 150°to make the seat width
match the standard. Then perform seat
correction as described in 2), and then carry out
lapping [A] and [B].
Grinding wheel angle
intake Exhaust
120 90
1 2
40 150
80