8. CYLINDER/PISTON
8-5
SERVICE INFORMATION (50cc-2T)
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
mm (in)
Item
Standard Service Limit
Cylinder head warpage
⎯ 0.1 (0.004)
Piston O.D.(3 mm, 0.12 in) from
bottom of piston skirt)
38.96～38.965 (15.584～15.586) 38.9 (1.556)
Cylinder-to- piston clearance
0.035～0.05 (0.0014～0.002) 0.1 (0.004)
Piston pin hole I.D.
12.002～12.008 (0.48008～0.48032) 12.03 (0.4812)
Piston pin O.D.
11.994～12 (0.47976～0.48) 11.98 (0.4792)
Piston-to-piston pin clearance
0.002～0.014 (0.00008～0.00056) 0.03 (0.0012)
Piston ring end gap (top/second)
0.1～0.25 (0.004～0.01) 0.4 (0.016)
Connecting rod small end I.D.
17.005～17.017 (0.6802～0.68068) 17.03 (0.6812)
Cylinder bore
39.005～39.01 (1.5602～1.5604) 39.05 (1.562)
TORQUE VALUES
Cylinder head bolt 10 N-m (1 kgf-m, 7 lbf-ft)
Spark plug 15 N-m (1.5 kgf-m, 11 lbf-ft)
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
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