7. CYLINDER HEAD/CYLINDER/PISTON ATV 50
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 Unit: mm (in)
Item Standard Service Limit
Cylinder head warpage 0.1 (0.004)
Piston O.D.(5mm from bottom of piston skirt) 38.97 (1.5588).38.955 (1.5582) 38.9 (1.556)
Cylinder-to- piston clearance 0.03 (0.0012)0.07 (0.0028) 0.1 (0.004)
Piston pin hole I.D. 12.002 (0.48008)12.008 (0.48032) 12.03 (0.4812)
Piston pin O.D. 11.994 (0.47976)12 (0.48) 11.98 (0.4792)
Piston-to-piston pin clearance 0.002 (0.00008)0.014 (0.00056) 0.03 (0.0012)
Piston ring end gap (top/second) 0.1 (0.004)0.25 (0.01) 0.4 (0.016)
Connecting rod small end I.D. 17.005 (0.6802)17.017 (0.68068) 17.03 (0.6812)
Cylinder bore 39 (1.56)39.025 (1.561) 39.05 (1.562)
TORQUE VALUES
Cylinder head bolt 1.6 kgf-m (16 N-m, 11.5 lbf-ft)
Exhaust muffler joint lock nut 1.2 kgf-m (12 N-m, 8.6 lbf-ft)
Exhaust muffler lock bolt 3.3 kgf-m (33 N-m, 23.8 lbf-ft)
Spark plug 1.4 kgf-m (14 N-m, 10.1 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
7-2
4.7 / 5