Problem With Shifting; Engine Makes Abnormal Noise - Benelli TNT 25 Maintenance Manual

Problem with shifting:

Can't engage the gear;
reset:
Clutch cannot be separated;
Shifting fork is bent or stuck;
Shifting gear stuck.
Shift positioning roller is blocked
Shift returning spring has poor flexibility or is damaged;
Shift shaft return spring pin is loosened;
The shift shaft return spring is damaged
The shift shaft is damaged
The shifting pawl is damaged
Jumps out of gear
Shift fork is worn or bent;
Shifting gear groove is worn;
Gear dogs or gear dog holes is worn;
Shift drum groove is worn;
Gear positioning roller spring has poor flexibility or is
damaged;
Shift fork guide pin is worn;
Drive shaft, output shaft and / or gear spline is worn
Over gear Shifting:
Gear positioning roller spring has poor flexibility or is
damaged;
Shift shaft return spring is broken ;
shift pedal cannot be

Engine makes abnormal noise:

"Click" fault sound:
Engine control unit (ECU) fault
Carbon deposition in combustion chamber;
Fuel quality is poor or fuel type is unsuitable;
Spark plug is unsuitable;
Engine is overheated
Knocking noise at piston:
The clearance between cylinder and piston is too large;
Cylinder and piston is worn;
Connecting rod is bent;
Piston pin or piston pin hole is worn;
Valve makes noise:
The valve clearance is incorrect;
Valve spring is damaged or the elasticity is poor;
Camshaft stop ring is worn;
Valve stem wear
Other noises:
The clearance at the small end of connecting rod is too large;
The clearance at the big end of connecting rod is too large;
The gap between the piston ring and the piston ring groove
is too large
Piston ring is worn, damaged or stuck;
Piston ring groove is worn;
Piston is seized or damaged;
Cylinder head gasket leaks;
The exhaust pipe of cylinder head connecting part leaks;
Crankshaft oscillation is too large;
Engine is loosened;
Crankshaft bearing is worn;
Main gear is worn or has a gap;
Timing chain tensioner fault;
Timing chain, sprocket or guide plate is worn;
The breathe valve is broken;
Secondary air inlet valve is broken;
Alternator rotor is loosened;
Overheating of muffler causes melting of catalytic converter
(Benelli emission control system)
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