YG125-30A Maintenance Manual
Inspection and adjustment
28
The main reasons for insufficient cylinder pressure
include:
Incorrect valve clearance adjusted
Valve leakage
Cylinder head sealing gasket ablated
Piston ring or cylinder worn
Piston ring worn
The main reasons for excessive pressure include:
Presence of accumulated carbon inside the
combustion chamber or on the piston top
Timing chain tension
Start the engine to run at idle speed.
Carefully listen to the sound given off by the running
engine: if the timing chain gives off ringing sound
“Dah
-
Dah”, it indicates insufficient tension of the chain
tensioner, replace it with a new one.
To replace the chain tensioner:
Unscrew the 2-M
6
×
16
socket cap screw to remove the
sealing washer and detach the old chain tensioner. Take
care not let the sealing washer and so on fall into the
crankcase. Insert the tensioner 4 locking key
into
the tail end of the new chain tensioner, turn and retract
the front end of the tensioner and lock it, then replace
with a new sealing washer, mount the new chain
tensioner and fasten.
Pull off the tensioner locking key to tension the timing
chain.
Replace with a new sealing washer and screw up the
bolts on the tail end of the chain tensioner.
Test cylinder
Turn the key clockwise
Press engine’s start button
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