Yanmar 3YM30, Service Manual

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5. Inspection and servicing of basic engine parts
131R1
5.7 Timing gear
The timing gear is helical type for minimum noise and specially treated for high durability.
5.7.1 Inspecting the gears
(1) Inspect the gears and replace if the teeth are damaged or worn.
(2) Measure the backlash of all gears that mesh, and replace the meshing gears as a set if
wear exceeds the limit.
NOTE:
If backlash is excessive, it will not only result in excessive noise and gear damage, but also lead to bad
valve and fuel injection timing and a decrease in engine performance.
(3) Idling gear
The bushing is pressure fitted into the idling gear.
Measure the bushing inner diameter and the outer
diameter of the shaft, and replace the bushing or idling
gear shaft if the oil clearance exceeds the wear limit.
A, B and C are inscribed on the end of the idling gear.
When assembling, these marks should align with those
on the cylinder block.
5.7.2 Gear timing marks
Match up the timing marks on each gear when
assembling (A, B and C).
mm
Standard Limit
Backlash 0.06-0.12 0.14
mm
Standard Limit
Idle gear shaft
diameter
36.950-36.975 36.900
Idle gear bushing
inside dia.
37.000-37.025 37.075
Oil clearance 0.025-0.075 0.175
Idle gear
Idle gear bushing
Idle gear shaft
(Gear train)
C
C
A
B
B
Idle gear
Crankshaft gear
Direction of rotation
Fuel injection pump
drive gear
Camshaft gear
A