Yamaha YZF-R125 Service Manual: Checking the valves and valve guides

Yamaha YZF-R125 Service Manual / Engine / Valves and valve springs / Checking the valves and valve guides

The following procedure applies to all of the valves and valve guides.

1. Measure:

Valve-stem-to-valve-guide clearance Out of specification Replace the
valve guide.

Valve-stem-to-valve-guide clearance = Valve guide inside diameter "a" - Valve stem diameter "b"

Checking the valves and valve guides

2. Replace:

Valve guide

NOTE:

To ease valve guide removal and installation, and to maintain the correct fit, heat the cylinder head to 100 C (212 F) in an oven.

a. Remove the valve guide with the valve guide remover "1".

Checking the valves and valve guides

b. Install the new valve guide with the valve guide installer "2" and valve guide remover "1".

Checking the valves and valve guides

a. Valve guide position

c. After installing the valve guide, bore the valve guide with the valve guide reamer "3" to obtain the proper valve-stem-to-valve-guide clearance.

Checking the valves and valve guides

NOTE:

After replacing the valve guide, reface the valve seat.

3. Eliminate:

Carbon deposits (from the valve face and valve seat)

4. Check:

Valve face Pitting/wear Grind the valve
face.
Valve stem end Mushroom shape or diameter larger than the body of the valve stem Replace
the valve.

5. Measure:

Valve margin thickness D "a" Out of specification Replace
the valve.

Checking the valves and valve guides

6. Measure:

Valve stem runout Out of specification Replace
the valve.

NOTE:

When installing a new valve, always replace the valve guide.
If the valve is removed or replaced, always replace the valve stem seal.

Checking the valves and valve guides

Removing the valves

The following procedure applies to all of the valves and related components. NOTE: Before removing the internal parts of the cylinder head (e.g., valves, valve springs, valve seats), make sure th ...

Checking the valve seats

The following procedure applies to all of the valves and valve seats. 1. Eliminate: Carbon deposits (from the valve face and valve seat) 2. Check: Valve seat Pitting/wear Replace the ...

Other materials:

Checking the cooling system
1. Remove: Side covers Upper side cowlings Refer to "GENERAL CHASSIS" on page 4-1. 2. Check: Radiator "1" Radiator inlet hose "2" Radiator outlet hose "3" Coolant reservoir hose "4" Water pump breather hose "5" Cracks/damage → Replace. Refer to "RADIATOR" on page 6-1 ...

Installing the steering head
1. Lubricate: Upper bearing Lower bearing Bearing races 2. Install: Lower ring nut Rubber washer Upper ring nut Lock washer Refer to "CHECKING AND ADJUSTING THE STEERING HEAD" on page 3-22. 3. Install: Upper bracket Steering stem nut NOTE: Temporarily tighten t ...

Checking and replacing the rear wheel sprocket
1. Check: Rear wheel sprocket More than 1/4 tooth "a" wear Replace the rear wheel sprocket. Bent teeth Replace the rear wheel sprocket. b. Correct 1. Drive chain roller 2. Rear wheel sprocket 2. Replace: Rear wheel sprocket a. Remove the self-locking nuts and the ...