TOHATSU MFS 25D Service Manual page 192

Power Unit
17) Inspection of Valve
1. Check the valve for dents and wear on the face. Replace if
necessary.
Measure the valve stem outer diameter a. Replace if less
2.
than the specified value.
Valve Stem Outer Diameter a: Standard Value
Intake Side: 5.48 mm (0.2157 in)
Exhaust Side: 5.46 mm (0.2150 in)
Functional Limit:
Intake Side: 5.46 mm (0.2150 in)
Exhaust Side: 5.44 mm (0.2142 in)
3. Measure the valve stem runout. Replace if greater than
the specified value.
Valve Stem Runout Limit:
Intake Side: 0.05 mm (0.0020 in)
Exhaust Side: 0.03 mm (0.0012 in)
18) Inspection of Valve Guide
Before inspecting the valve guide, check that the
valve stem outer diameter is within the specified
limit.
Measure the valve guide inner diameter a. Replace the
1.
cylinder head if greater than the specified value.
Valve Guide Inner Diameter a: Standard Value
Intake/Exhaust Side: 5.51 mm (0.2169 in)
Functional Limit:
Intake Side: 5.55 mm (0.02185 in)
Exhaust Side: 5.57 mm (0.02193 in)
2. Calculate the clearance between the valve guide and
valve stem as described below. Replace the cylinder head
and/or valve if greater than the specified value.
Clearance between valve guide and valve stem =
Valve Guide Inner Diameter a
Diameter b:
Intake Side: 0.008-0.040 mm (0.00031-0.00157 in)
Exhaust Side: 0.025-0.057 mm (0.00098-0.00224 in)
Functional Limit
Intake Side: 0.070 mm (0.00276 in)
Exhaust Side: 0.100 mm (0.00394 in)
5-52
b
4st 25/30 2022