Service Information; Troubleshooting - KYMCO MXU 50 REVERSE Service Manual

7
CYLINDER HEAD/CYLINDER/PISTON
.

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
Item
Cylinder head warpage
Piston O.D.(5mm from bottom of piston skirt)
Cylinder-to- piston clearance
Piston pin hole I.D.
Piston pin O.D.
Piston-to-piston pin clearance
Piston ring end gap (top/second)
Connecting rod small end I.D.
Cylinder bore
TORQUE VALUES
Cylinder head bolt
Exhaust muffler joint lock nut 1.2 kgf-m (12 N-m, 8.6 lbf-ft)
Exhaust muffler lock bolt
Spark plug

TROUBLESHOOTING

Compression too low, hard starting
or poor performance at low speed
• Leaking cylinder head gasket
• Loose spark plug
• Worn, stuck or broken piston and piston rings
• Worn or damaged cylinder and piston
Compression too high, overheating
or knocking
• Excessive carbon build-up in cylinder head
or on piston head
38.97 (1.5588).
0.03 (0.0012)～0.07 (0.0028)
12.002 (0.48008)
11.994 (0.47976)
0.002 (0.00008)
～
0.1 (0.004) 0.25 (0.01)
17.005 (0.6802)
～
39 (1.56) 39.025 (1.561)
1.6 kgf-m (16 N-m, 11.5 lbf-ft)
3.3 kgf-m (33 N-m, 23.8 lbf-ft)
1.4 kgf-m (14 N-m, 10.1 lbf-ft)
Abnormal noisy piston
• Worn cylinder and piston
• Worn piston pin or piston pin hole
• Worn connecting rod small end bearing
Abnormal noisy piston rings
• Worn, stuck or broken piston rings
• Worn or damaged cylinder
Standard
⎯
0.1 (0.004)
～
38.955 (1.5582) 38.9 (1.556)
0.1 (0.004)
～
12.008 (0.48032) 12.03 (0.4812)
～
12 (0.48) 11.98 (0.4792)
～
0.014 (0.00056) 0.03 (0.0012)
0.4 (0.016)
～
17.017 (0.68068) 17.03 (0.6812)
39.05 (1.562)
ATV 50
Unit: mm (in)
Service Limit
7-2