Kymco MO BW 50 Service Manual - chap 06 (testa e cilindro)

6. CYLINDER HEAD/CYLINDER/PISTON

6-0

BET & WIN 5 0

6

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CYLINDER HEAD/CYLINDER/PISTON

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SERVICE INFORMATION........................................................ 6-1

TROUBLESHOOTING.............................................................. 6-1

CYLINDER HEAD.................................................................... 6-2

CYLINDER/PISTON................................................................. 6-4

6

6. CYLINDER HEAD/CYLINDER/PISTON

6-1

BET & WIN 5 0

SERVICE INFORMATION

GENERAL INSTRUCTIONS

• The cylinder head, cylinder and piston can be serviced with the engine installed in the frame.

• Before disassembly, clean the engine to prevent dust from entering the engine.

• Remove all gasket material from the mating surfaces.

• Do not use a driver to pry between the cylinder and cylinder head, cylinder and crankcase.

• Do not damage the cylinder inside and the piston surface.

• After disassembly, clean the removed parts before inspection. When assembling, apply the

specified engine oil to movable parts.

SPECIFICATIONS

Standard (mm)

Service Limit (mm)

Item

B&W50

B&W50

Cylinder head warpage



0.10

Piston O.D.(5mm from bottom of piston

38.970_ 38.955

38.90

Cylinder-to- piston clearance

0.03_ 0.07

0.10

Piston pin hole I.D.

12.002_ 12.008

12.03

Piston pin O.D.

11.994_ 12.0

11.98

Piston-to-piston pin clearance

0.002_ 0.014

0.03

Piston ring end gap (top/second)

0.10_ 0.25

0.40

Connecting rod small end I.D.

17.005_ 17.017

17.03

Cylinder bore

39.0_ 39.025

39.05

TORQUE VALUES

Cylinder head bolt 14.7_ 16.66N-m
Exhaust muffler joint lock nut 9.8_ 13.72N-m
Exhaust muffler lock bolt 29.4_ 35.28N-m
Spark plug 10.78_ 16.66N-m

TROUBLESHOOTING

Compression too low, hard starting
or poor performance at low speed Abnormal noisy piston

• Leaking cylinder head gasket • Worn cylinder and piston

• Loose spark plug • Worn piston pin or piston pin hole

• Worn, stuck or broken piston and piston rings • Worn connecting rod small end bearing

• Worn or damaged cylinder and piston

Compression too high, overheating
or knocking Abnormal noisy piston rings

• Excessive carbon build-up in cylinder head • Worn, stuck or broken piston rings
or on piston head • Worn or damaged cylinder

6. CYLINDER HEAD/CYLINDER/PISTON

6-2

BET & WIN 5 0

CYLINDER HEAD

REMOVAL

Remove the rear carrier.
Remove the frame body cover. (2-2)
Drain the coolant.
Disconnect the thermosensor wire from the
thermosensor.
Disconnect the water hose from the
thermostat housing.

Remove the spark plug cap.
Remove the two joint lock nuts on the front
of the exhaust muffler and then remove the
two exhaust muffler lock bolts.
The installation sequence is the reverse of
removal.

Remove the spark plug.
Remove the cylinder head bolts and the
cylinder head.

Remove the cylinder head gasket.

Cylinder head Bolts

Exhaust muffler joint lock nut

Bolts

Cylinder Head

Spark Plug

Spark Plug Cap

When installing the exhaust muffler,
first tighten the two nuts on the front
and then tighten the two bolts.

°Ø

Loosen the bolts diagonally in 2 or 3
times.

°Ø