Compression too low, hard starting or poor performance al low speed

• Valves:

– Incorrect valve adjustment

– Burned or bent valve

– Incorrect valve timing

– Weak valve spring

– Uneven valve seating

– Valve stuck open

• Cylinder head:

– Leaking or damaged cylinder head gasket

– Warped or cracked cylinder head

– Loose spark plug

• Faulty cylinder, piston or piston rings (page 11-3).

 

Compression too high, over-heating or knocking

• Excessive carbon build-up on piston head or combustion chamber

 

Excessive smoke

• Worn valve stem or valve guide

• Damaged stem seal

• Faulty cylinder, piston or piston rings (page 11-3).

 

Excessive noise

• Incorrect valve adjustment

• Sticking valve or broken valve spring

• Worn or damaged camshaft

• Worn rocker arm and/or shaft

• Worn rocker arm and valve stem end

• Worn cam sprocket teeth

• Worn and loose cam chain

• Worn or damaged cam chain tensioner

• Faulty cylinder, piston or piston rings (page 11-3).

 

Rough idle

• Low cylinder compression

• Faulty fuel system

 

10-2

CYLINDER HEAD/VALVES

COMPONENT LOCATION

10 N·m (1.0 kgf·m, 7 lbf·ft)

 

12 N·m (1.2 kgf·m, 9 lbf·ft)

 

 

45 N·m (4.6 kgf·m, 33 lbf·ft)

 

 

4.2 N·m (0.4 kgf·m, 3.1 lbf·ft)

 

10-3

CYLINDER HEAD/VALVES

CYLINDER COMPRESSION

 

 

To avoid discharging the battery, do not operate the starter motor for more than 7 seconds.

 

Warm the engine to normal operating temperature. Stop the engine.

Remove the spark plug (page 3-5).

 

Install the compression gauge [1] into the spark plug hole.

 

Turn the ignition switch ON and engine stop switch " ". Shift the transmission into neutral.

 

Open the throttle all the way and crank the engine with the starter motor until the gauge reading stops rising.

 

STANDARD:

 

1,294 kPa at 490 min^-1 (rpm) (13.2 kgf/cm², 188 psi)

 

Low compression can be caused by:

 

– Blown cylinder head gasket

– Improper valve adjustment

– Valve leakage

– Worn piston ring or cylinder

 

High compression can be caused by:

 

– Carbon deposits in combustion chamber or on piston head

 

 

[1]

 

CYLINDER HEAD COVER

 

REMOVAL

 

Remove the following:

– Spark plug cap (page 3-5)

– PAIR check valve (page 7-18)

– Fuel tank (page 7-8)

– Ignition coil (page 5-6)

 

Remove the three bolts [1] and ground terminal [2] from the radiator reserve tank stay.

 

[1]

 

Remove the cylinder head cover bolts [1], rubber seals [2], cylinder head cover [3] and packing [4].

 

 

[3]/[4]

 

[1]/[2]

 

 

[1]/[2]

 

10-4

CYLINDER HEAD/VALVES

 

INSTALLATION

 

Apply sealant (Three bond 5211C, 1207B, 1215, SS KE45 or equivalent) to the cylinder head semi-circular cut-outs as shown.

 

 

Install a new packing [1] into the cylinder head cover [2] groove.

 

Install the cylinder head cover onto the cylinder head.

 

 

Check the rubber seals [1] are in good condition, replace them if necessary.

 

Install the rubber seals to the cylinder head cover with their "UP" marks [2] facing up.

 

 

Install and tighten the cylinder head cover bolts [1] to the specified torque.

 

TORQUE:10 N·m (1.0 kgf·m, 7 lbf·ft)

 

[2]

 

[2]

 

 

[1]

 

[1]

 

[1]

 

 

10-5

CYLINDER HEAD/VALVES

 

Set the radiator reserve tank stay and ground terminal [1] in position.

 

Install and tighten the three bolts [2]. Install the following:

– Ignition coil (page 5-6)

– PAIR check valve (page 7-18)

– Fuel tank (page 7-8)

– Spark plug cap (page 3-5)

 

 

CAMSHAFT

 

REMOVAL

 

Remove the cylinder head cover (page 10-4).

 

Make sure the piston is at TDC (Top Dead Center) on the compression stroke (page 3-6).

 

Remove the cam chain tensioner lifter plug [1] and O-ring [2].

 

Turn the cam chain tensioner lifter shaft fully in (clockwise) and secure it using a tensioner stopper [1] to prevent damaging the cam chain.

 

TOOL:
Tensioner stopper	070MG-0010100

 

Be careful not to let Remove the bolts [1] and cam chain guide B [2]. the cam chain

 

guide bolts fall into the crankcase.

[1]/[2]

 

[2]

 

 

[1]

 

 

[2]

 

[1]

[2]

 

 

[1]

 

 

10-6

CYLINDER HEAD/VALVES

 

Be careful not to let Remove the bolts [1] and camshaft holders [2]. the camshaft holder

bolts fall into the

_crankcase. From outside to inside, loosen the bolts in a crisscross pattern in several steps or the camshaft holder might

 

break.

 

Attach a piece of Remove the camshafts [1] by removing the cam chain wire to the cam [2] from the cam sprockets.

chain to prevent it from falling into the crankcase.

 

 

Lift the rocker arms [1].

 

Remove the shims [2].

• Do not allow the shims to fall into the crankcase.

• Mark all shims to ensure correct reassembly in their original locations.

 

• The shims can be easily removed with a tweezers or a magnet.

 

INSPECTION

 

Inspect the following parts for damage, abnormal wear, deformation, burning or clogs in oil passages.

 

– Cam sprocket

– Camshaft

– Camshaft holder/dowel pin

– Cam chain guide B

 

Measure each part according to CYLINDER HEAD/

VALVES SPECIFICATIONS (page 1-6).

Replace any part if it is out of service limit.

[1]

 

[2]

[2]

 

 

		[1]
[2]		[1]

 

[1]

 

 

10-7

CYLINDER HEAD/VALVES

 

 

Do not rotate the camshaft when using plastigauge.

 

 

Be sure the dowel pins in the camshaft holder align the holes in the cylinder head.

 

CAMSHAFT OIL CLEARANCE

 

Wipe any oil from the journals of the camshaft, cylinder

head and camshaft holders. ^[1] Lay a strip of plastigauge [1] lengthwise on top of each

 

camshaft journal.

 

Install each camshaft holder to the correct locations
[1]
with the identification marks [1].
– "R" mark: right camshaft holder
– "L" mark: left camshaft holder
– "IN" mark: intake side
– "EX" mark: exhaust side

 

Apply engine oil to the camshaft holder mounting bolt

[1]

[1] threads and seating surface.

Failure to tighten the camshaft holder in a crisscross

pattern may cause a camshaft holder to break.

Tighten all camshaft holder mounting bolts to the

specified torque.

TORQUE:12 N·m (1.2 kgf·m, 9 lbf·ft)

From inside to outside, tighten the bolts in a crisscross pattern in several steps.

 

Remove the camshaft holders and measure the width of each plastigauge.

The widest thickness determines the oil clearance.