Piston: Testing and Inspection

1. The cylinder bore size block's front upper surface.

NOTE: Standard sized pistons are classified into two grades, "A" and "B". These grades should be used as a guideline in selecting a standard piston.

Standard diameter:
A: 96.905 - 96.915 mm (3.8151 - 3.8155 inch)
B: 96.895 - 96.905 mm (3.8148 - 3.8151 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 shown, using a cylinder bore gauge.

CAUTION: Measurement should be performed at a temperature 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 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 shown. (Thrust direction)

CAUTION: Measurement should be performed at a temperature of 20°C (68°F).

Piston grade point H: 40.0 mm (1.575 inch)

Piston outer diameter:
- A: 96.885 - 96.895 mm (3.8144 - 3.8148 inch)
- B: 96.875 - 96.885 mm (3.8140 - 3.8144 inch)
- 0.25 mm (0.0098 inch) oversize: 97.115 - 97.145 mm (3.8234 - 3.8246 inch)
- 0.50 mm (0.0197 inch) oversize: 97.365 - 97.395 mm (3.8333 - 3.8344 inch)

5. Calculate the clearance between cylinder and piston.

CAUTION: Measurement should be performed at a temperature of 20°C (68°F).

Cylinder to piston clearance at 20°C (68°F):
- Standard: 0.010 - 0.030 mm (0.0004 - 0.0012 inch)
- Limit: 0.050 mm (0.0020 inch)

6. Boring and honing
a. If the value of taper, out-of-roundness, or cylinder-to-piston clearance measured exceeds the specified limit 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 the limit after boring and honing, replace the crankcase

CAUTION: Immediately after reboring, the cylinder diameter may differ from its real diameter due to temperature rise. Thus, pay attention to this when measuring the cylinder diameter. Limit of cylinder enlarging (boring): 0.5 mm (0.020 inch)