Yamaha XMAX YP125R - Service manual > Cylinder head (YP250R)

Removing the cylinder head

Removing the cylinder head

Removing the cylinder head

1. Align:

• "I" mark "a" on the generator rotor (with the stationary pointer "b" on the generator cover)

a. Turn the primary sheave nut on the left side of the crankshaft counterclockwise to turn the crankshaft.

b. When the piston is at TDC on the compression stroke, align the "I" mark "c" on the camshaft sprocket with the stationary pointer "d" on the cylinder head.

2. Loosen:

• Camshaft sprocket bolt "1"

TIP

While holding the primary sheave nut with a wrench, remove the camshaft sprocket bolt.

3. Remove:

• Timing chain tensioner (along with the gasket)
• Camshaft sprocket bolt "1"
• Camshaft sprocket plate "2"
• Camshaft sprocket

TIP

To prevent the timing chain from falling into the crankcase, fasten it with a wire "3".

4. Remove:

• Cylinder head

TIP

• Loosen the bolts and nuts in the proper sequence as shown.
• Loosen each bolt and nut 1/2 of a turn at a time. After all of the bolts and nuts are fully loosened, remove them.

Checking the cylinder head

1. Eliminate:

• Combustion chamber carbon deposits (with a rounded scraper)

TIP

Do not use a sharp instrument to avoid damaging or scratching:

• Spark plug bore threads
• Valve seats

2. Check:

• Cylinder head

Damage/scratches → Replace.

• Cylinder head water jacket

Mineral deposits/rust → Eliminate.

3. Measure:

• Cylinder head warpage

Out of specification → Resurface the cylinder head.

Warpage limit 0.05 mm (0.0020 in)

a. Place a straightedge "1" and a thickness gauge "2" across the cylinder head.

b. Measure the warpage.

c. If the limit is exceeded, resurface the cylinder head as follows.

d. Place 400-600 grit wet sandpaper on the surface plate and resurface the cylinder head using a figure-eight sanding pattern.

TIP

To ensure an even surface, rotate the cylinder head several times.

Checking the camshaft sprocket

1. Check:

• Camshaft sprocket

More than 1/4 tooth wear "a" → Replace the camshaft sprocket, timing chain and crankshaft as a set.

a. 1/4 tooth

b. Correct

1. Timing chain roller

2. Camshaft sprocket

Checking the timing chain tensioner

1. Check:

• Timing chain tensioner

Cracks/damage → Replace.

2. Check:

• One-way cam operation

Rough movement → Replace the timing chain tensioner housing.

3. Check:

• Cap bolt
• Spring
• One-way cam
• Timing chain tensioner rod

Damage/wear → Replace the defective part(s).

Installing the cylinder head

1. Tighten:

• Cylinder head nuts "1"

Cylinder head nut 22 Nm (2.2 m*kgf, 16 ft*lbf)

• Cylinder head bolts "2"

Cylinder head bolt 10 Nm (1.0 m*kgf, 7.2 ft*lbf)

TIP

• Lubricate the cylinder head nuts and washers with engine oil.
• Tighten the cylinder head nuts and bolts in the proper tightening sequence as shown and torque them in two stages.

2. Install:

• Dowel pin "1"
• Camshaft sprocket "2"
• Timing chain "3"
• Camshaft sprocket plate
• Washer
• Camshaft sprocket bolt

a. Turn the primary sheave nut on the left side of the crankshaft counterclockwise to turn the crankshaft.

b. Align the "I" mark "a" on the generator rotor with the stationary pointer "b" on the generator cover.

c. Align the "I" mark "c" on the camshaft sprocket with the stationary pointer "d" on the cylinder head.

d. Install the timing chain onto the camshaft sprocket, and then install the camshaft sprocket onto the camshaft.

TIP

• When installing the camshaft sprocket, be sure to keep the timing chain as tight as possible on the exhaust side.
• Align the dowel pin "1" on the camshaft with the slot in the camshaft sprocket.

NOTICE

Do not turn the crankshaft when installing the camshaft to avoid damage or improper valve timing.

e. Install the camshaft sprocket plate and camshaft sprocket bolt.

f. While holding the primary sheave nut, temporarily tighten the camshaft sprocket bolt.

g. Remove the wire from the timing chain.

3. Install:

• Timing chain tensioner gasket
• Timing chain tensioner

a. Remove the timing chain tensioner cap bolt "1" and spring "2".

b. Release the timing chain tensioner one-way cam "3" and push the timing chain tensioner rod "4" all the way into the timing chain tensioner housing.

c. Install the timing chain tensioner and gasket "5" onto the cylinder.

Timing chain tensioner bolt 10 Nm (1.0 m*kgf, 7.2 ft*lbf)

d. Install the spring and timing chain tensioner cap bolt.

Timing chain tensioner cap bolt 8 Nm (0.8 m*kgf, 5.8 ft*lbf)

4. Turn:

• Crankshaft (turn the primary sheave nut on the left side of the crankshaft several turns counterclockwise)

5. Check:

• "I" mark "a"

Make sure the "I" mark "a" on the generator rotor is aligned with the stationary pointer "b" on the generator cover.

• "I" mark "c"

Make sure the "I" mark "c" on the camshaft sprocket is aligned with the stationary pointer "d" on the cylinder head.

Out of alignment → Correct.

Refer to the installation steps above.

6. Tighten:

• Camshaft sprocket bolt

Camshaft sprocket bolt 60 Nm (6.0 m*kgf, 43 ft*lbf)

NOTICE

Be sure to tighten the camshaft sprocket bolt to the specified torque to avoid the possibility of the bolt coming loose and damaging the engine.

7. Measure:

• Valve clearance

Out of specification → Adjust.

See also: