KYMCO ZX/SCOUT 50, Service Manual

Page: 59 / 191

6
. CYLINDER HEAD/CYLINDER/PISTON
6-2
ZX / SCOUT
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 SC10AS SC10AS
Cylinder head warpage
⎯
0.10
Piston O.D.(5mm from bottom of piston
38.955 38.970 38.90
Cylinder-to- piston clearance
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
← ←
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 1.5 1.7kg-m
Exhaust muffler joint lock nut 1.0 1.4kg-m
Exhaust muffler lock bolt
3.0 3.6kg-m
Spark plug 1.1 1.7kg-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