TOHATSU MFS 25D Service Manual page 196

Power Unit
9. Apply a thin coat of an abrasive compound to the entire
valve seat contact area, and rub and polish the valve seat
while knocking and turning the valve with a valve lapper
(commercially available).
Perform the work by taking care not to
allow the abrasive compound to adhere to
the valve stem and valve guide.
• Use a finer abrasive compound to finish.
• When changing the abrasive compound to a
finer one, remove the present one completely.
• After completion of lapping, wipe off the
compound and then clean.
10. After the work, remove the compound completely from the
cylinder head and valve.
Check the valve seat contact width c.
11.
Valve Seat Contact Width c: Standard Value
1.0 mm (0.04 in)
21) Inspection of Rocker Arm and
Rocker Arm Shaft
1. Check the rocker arm, rocker arm shaft, and rocker arm
contact area a for wear. Replace if necessary.
Measure the rocker arm inner diameter b and rocker arm
2.
shaft outer diameter c. Calculate the oil clearance d (d
= b c). Replace if other than the specified value.
Rocker Arm Inner Diameter b:
Standard Value
13.01 mm (0.5129 in)
Rocker Arm Shaft Outer Diameter c:
Standard Value
12.99 mm (0.5114 in)
Oil Clearance Between Rocker Arm Hole and
Shaft d: b - c
0.006 - 0.035 mm (0.00024 - 0.00138 in)
Functional Limit:
Replace if b is 13.05 mm (0.5138 in) or greater
Replace if c is 12.94 mm (0.5094 in) or less
Replace if d is 0.060 mm (0.00236 in) or greater
5-56
CAUTION
D = b c
b
c
45˚
4st 25/30 2022