Yanmar 3YM30, Service Manual

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5. Inspection and servicing of basic engine parts
118R1
5.3.3 Piston rings
There are two compression rings and one oil ring.
The absence of an oil ring on the piston skirt prevents
oil from being kept on the thrust surface and in turn
provides good lubrication.
(1) Measuring the rings.
Measure the thickness and width of the rings, and the
ring-to-groove clearance after installation. Replace if
wear exceed the limit.
3YM30 mm
Standard Limit
Top ring
Groove width 1.550-1.570 -
Ring width 1.470-1.490 1.450
Clearance 0.060-0.100 -
Second ring
Groove width 1.580-1.595 1.695
Ring width 1.430-1.450 1.410
Clearance 0.013-0.165 0.285
Oil ring
Groove width 3.010-3.030 3.130
Ring width 2.970-2.990 2.950
Clearance 0.020-0.060 0.180
3YM20/2YM15 mm
Standard Limit
Top ring
Groove width 1.550-1.570 -
Ring width 1.470-1.490 1.450
Clearance 0.060-0.100 -
Second ring
Groove width 1.540-1.560 1.660
Ring width 1.470-1.490 1.450
Clearance 0.050-0.090 0.210
Oil ring
Groove width 3.010-3.030 3.130
Ring width 2.970-3.010 2.950
Clearance 0.020-0.060 0.180
(Ring components)
Top ring
Oil ring
Second ring
Width
Thickness
(Measuring side clearance)