Piston: Testing and Inspection
INSPECTIONPistons
^ Inspect piston for faults, cracks or other damaged. Damaged or faulty piston should be replaced.
^ Piston diameter: As indicated in figure, piston diameter should be measured at a position 15 mm (0.59 inch) from piston skirt end in the direction perpendicular to piston pin.
Piston Diameter:
Standard: 74.970 - 94.990 mm (2.9516-2.9523 inch)
Oversize 0.25 mm (0.0098 inch): 75.220 - 75.230 mm (2.9614 - 2.9618 inch)
0.50 mm (0.0196 inch): 75.470-75.480 mm (2.9712 - 2.9716 inch)
^ Piston clearance: Measure cylinder bore diameter and piston diameter to find their difference which is piston clearance. Piston clearance should be within specification as given below. If it is out of specification, rebore cylinder and use oversize piston.
Piston Clearance: 0.02 - 0.04 mm (0.0008 - 0.0015 inch)
NOTE: Cylinder bore diameters used here are measured in thrust direction at two positions.
^ Ring groove clearance: Before checking, piston grooves must be clean, dry and free of carbon. Fit new piston ring into piston groove, and measure clearance between ring and ring land by using thickness gauge. If clearance is out of specification, replace piston.
Ring Groove Clearance:
Top: 0.03 - 0.07 mm (0.0012 - 0.0027 inch)
2nd: 0.02 - 0.06 mm (0.0008 - 0.0023 inch)
Piston Pin
^ Check piston pin, connecting rod small end bore and piston bore for wear or damage, paying particular attention to condition of small end bore bush. If pin, connecting rod small end bore or piston bore is badly worn or damaged, replace pin, connecting rod or piston.
^ Piston pin clearance: Check piston pin clearance in small end. Replace connecting rod if its small end is badly worn or damaged or if measured clearance exceeds limit.
Piston Clearance In Small End:
Standard: 0.003 - 0.016 mm (0.0001 - 0.0006 inch).
Limit: 0.05 mm (0.0020 inch).
Small-End Bore: 19.003 - 19.011 mm (0.7482 - 0.7486 inch).
Piston Pin Diameter: 18.995 - 19.000 mm (0.7479 - 0.7480 inch).
Piston Rings
To measure end gap, insert piston ring into cylinder bore and then measure the gap by using thickness gauge. If measured gap is out of specification, replace ring.
Piston Ring End Gap:
Top Ring:
Standard: 0.2 - 0.35 mm (0.0079-0.0137 inch)
Limit: 0.7 mm (0.0275 inch)
2nd Ring:
Standard: 0.2 - 0.35 mm (0.0079 - 0.0137 inch)
Limit: 0.7 mm (0.0275 inch)
Oil Ring;
Standard: 0.2 - 0.7 mm (0.0079 - 0.0275 inch)
Limit: 1.7 mm (0.0669 inch)
NOTE: Decarbon and clean top of cylinder bore before inserting piston ring.