mxu 50 Workshop-manual : Page 111

          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




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