Piston: Testing and Inspection
InspectionCylinder And Piston
1. The cylinder bore size is stamped on the cylinder block's front upper surface.
NOTE:
^ Measurement should be performed at a temperature of 20°C (68°F).
^ Standard sized pistons are classified into two grades, "A" and "B". These grades should be used as guide lines in selecting a standard piston.
Standard diameter.
99.505 - 99.515 mm (3.9175 - 3.9179 inch)
99.495 - 99.505 mm (3.9171 - 3.9175 inch)
2. How to measure the inner diameter of each cylinder:
Measure the inner diameter of each cylinder in both the thrust and piston pin directions at the heights as shown in the figure, using a cylinder bore gauge.
NOTE: Measurement should be performed at a temperature of 20°C (68°F).
Taper.
Standard 0.015 mm (0.0006 inch)
Limit 0.050 mm (0.0020 inch)
Out-of-roundness:
Standard 0.010 mm (0.0004 inch)
Limit 0.050 mm (0.0020 inch)
3. When the piston is to be replaced due to general or cylinder wear, determine a suitable sized piston by measuring the piston clearance.
4. How to measure the outer diameter of each piston: Measure the outer diameter of each piston at the height as shown in the figure. (Thrust direction)
NOTE: Measurement should be performed at a temperature of 20°C (68°F).
Piston grade point H: 38.2 mm (1.504 inch)
Standard
99.505 - 99.515 mm (3.9175 - 3.9179 inch)
99.495 - 99.505 mm (3.9171 - 3.9175 inch)
0.25 mm (0.0098 inch) oversize: 99.745 - 99.765 mm (3.9270 - 3.9278 inch)
0.50 mm (0.0197 inch) oversize: 99-995 - 100.015 mm (3.9368 - 3.9376 inch)
5. Calculate the clearance between cylinder and piston.
NOTE: Measurement should be performed at a temperature of 20°C (68°F).
Cylinder to piston clearance at 20°C (68°F):
Standard -0.010 - 0.010 mm (-0.00039 - 0.00039 inch)
Limit 0.030 mm (0.0012 inch)
6. Boring and honing
a. If the value of taper, out-of-roundness, or cylinder-to-piston clearance measured exceeds the standard value or if there is any damage on the cylinder wall, rebore it to use an oversize piston.
CAUTION: When any of the cylinders needs reboring, all other cylinders must be bored at the same time, and use oversize pistons. Do not perform boring on one cylinder only. Nor use an oversize piston for one cylinder only.
b. If the cylinder inner diameter exceeds limit after boring and honing, replace the cylinder block.
Limit of cylinder inner diameter (diameter): 100. 005 mm (3.937 inch)
NOTE: Immediately after reboring, the cylinder diameter may differ from its real diameter due to temperature rise. Thus, pay attention when measuring the cylinder diameter.
Piston And Piston Pin
1. Check the pistons and piston pins for damage, cracks and wear, and the piston ring grooves for wear and damage. Replace if defective.
2. Measure the piston-to-cylinder clearance at each cylinder. If any of the clearances is not within the standard value, replace the piston. Or bore the cylinder to use an oversize piston.
3. Make sure that the piston pin can be inserted into the piston pin hole with a thumb at 200C (680F). Replace if defective.
Clearance between piston hole and piston pin:
Standard 0.004 - 0.008 mm (0.0002 - 0.0003 inch)
Limit 0.020 mm (0.0008 inch)
4. Check the snap ring installation groove (A) on the piston for burr. If necessary, remove burr from the groove so that the piston pin can lightly move.
5. Check the piston pin snap ring for distortion, cracks and wear.