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7-31

POWR

Power unit

2. Measure the valve spring tilt b. Replace

if above specification.

Checking the valve

1. Check the valve face. Replace the valve

if pitted or worn.

2. Measure the valve margin thickness a.

Replace if out of specification.

3. Measure the valve stem diameter b.

Replace if out of specification.

4. Measure the valve stem runout.

Checking the valve guide

Before checking the valve guide, make sure

to check the valve.

1. Measure the valve guide inside diameter

a. Replace if out of specification.

Valve spring free length a:

27.6 mm (1.09 in)

Valve spring tilt limit b: 1.0 mm (0.04 in)

Valve margin thickness a:

Intake:

0.800–1.200 mm (0.0315–0.0472 in)

Exhaust:

1.100–1.500 mm (0.0433–0.0591 in)

Valve stem diameter b:

Intake:

5.475–5.490 mm (0.2156–0.2161 in)

Exhaust:

5.460–5.475 mm (0.2150–0.2156 in)

Valve stem runout (reference data):

Intake: 0.050 mm (0.0020 in)

Exhaust: 0.030 mm (0.0012 in)

Yamaha F4B Service Manual

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