Yamaha MT-03 - Service manual > Cylinder head

Removing the cylinder head

1. Align:

• "I" mark "a" on the A.C. magneto rotor (with the stationary pointer "b" on the A.C. magneto cover)

a. Turn the crankshaft counterclockwise.

b. When the piston is at top dead center (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 bolts "1"

NOTE:

While holding the A.C. magneto rotor nut with a wrench, remove the bolt.

3. Loosen:

• Timing chain tensioner cap bolt

4. Remove:

• Timing chain tensioner (along with the gasket)
• Camshaft sprocket
• Timing chain

NOTE:

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

5. Remove:

• Cylinder head

NOTE:

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

Checking the cylinder head

1. Eliminate:

• Combustion chamber carbon deposits (with a rounded scraper)

NOTE:

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.

Maximum cylinder head warpage 0.03 mm (0.0012 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.

NOTE:

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

Checking the tappet covers and camshaft Sprocket cover

1. Check:

• Tappet covers "1"
• Camshaft sprocket cover "2"
• O-rings "3" Damage/wear → Replace the defective part(s).

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:

• Timing chain tensioner cap bolt
• Copper washer
• Spring
• One-way cam
• Gasket
• Timing chain tensioner rod Damage/wear → Replace the defective part(s).

Checking the camshaft sprocket

1. Check:

• Camshaft sprocket.

  Wear/damage → Replace the camshaft sprocket and timing chain as a set.

a. 1/4 of a tooth

b. Correct

1. Roller

2. Sprocket

Installing the cylinder head

1. Install:

• Dowel pins
• Cylinder head gasket

2. Install:

• Cylinder head
• Washers
• Cylinder head bolts

NOTE:

• Lubricate the cylinder head bolt threads and muting surface with engine oil.
• Install the washers with their blunt surface facing the bolt seat.

3. Tighten:

• Cylinder head bolts

Cylinder head bolts "1" L = 135 mm (5.31 in)

50 Nm (5.0 m*kg, 36 ft*lb) Cylinder head bolts "2"

L = 145 mm (5.71 in)

50 Nm (5.0 m*kg, 36 ft*lb)

Cylinder head bolts "3" 45 Nm (4.5 m*kg, 32 ft*lb)

Cylinder head bolts "4" 10 Nm (1.0 m*kg, 7.2 ft*lb)

NOTE:

Tighten the cylinder head bolts in the proper tightening sequence as shown and torque them in two stages.

4. Install:

• Camshaft sprocket (onto the camshaft)

NOTE:

Make sure that the projection "a" on the decompressor lever is in the position shown in the illustration.

a. Turn the primary pulley counterclockwise.

b. Align the "I" mark "b" on the A.C. magneto rotor with the stationary pointer "c" on the A.C. magneto cover.

c. Install the timing chain "1" onto the camshaft sprocket "2", then the camshaft sprocket onto the camshaft, and then finger tighten the camshaft sprocket bolts.

NOTE:

To install the camshaft sprocket, install the projection "3" on the camshaft sprocket into the slot "a" in the decompression lever.

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

NOTE:

• When installing the camshaft sprocket, be sure to keep the timing chain as tight as possible at the exhaust end of the chain.
• Align the projection on the camshaft with the slot in the camshaft sprocket.

CAUTION:

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

e. Remove the wire from the timing chain.

5. Install:

• Timing chain tensioner

a. Remove the timing chain tensioner cap bolt "1", copper washer "2" and spring "3".

b. Release the timing chain tensioner one-way cam "4" and push the timing chain tensioner rod "5" all the way into the timing chain ten-sioner housing.

c. Install the timing chain tensioner and gasket "6" onto the cylinder.

Timing chain tensioner bolt 10 Nm (1.0 m*kg, 7.2 ft*lb)

NOTE:

Install the gasket with its beaded side facing the timing chain tensioner end.

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

Timing chain tensioner cap bolt 20 Nm (2.0 m*kg, 14 ft*lb)

6. Turn:

• Crankshaft (several turns counterclockwise)

7. Check:

• "I" mark "a"

NOTE:

Check that the "I" mark "a" on the A.C. magneto rotor is aligned with the stationary pointer "b" on the A.C. magneto cover.

• "I" mark "c"

NOTE:

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

Out of alignment → Correct.

Repeat steps 4-7, if necessary.

8. Tighten:

• Camshaft sprocket bolts

Camshaft sprocket bolts 20 Nm (2.0 m*kg, 14 ft*lb)

CAUTION:

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

9. Measure:

• Valve clearance

Out of specification → Adjust.

See also: