Piston to Bore - Clearance

PISTON-TO-BORE CLEARANCE





1. Using a bore gauge, measure cylinder bore for wear, out-of-round and taper.
Standard inner diameter: 91.500 - 91.530 mm (3.6024 - 3.6035 inch)
Wear limit: 0.20 mm (0.0079 inch)
If it exceeds the limit, rebore all cylinders. Replace cylinder block if necessary.





Out-of-round (X - Y) standard: 0.015 mm (0.0006 inch)
Taper (A - B or A - C) standard: 0.015 mm (0.0006 inch)
2. Check for scratches and seizure. If seizure is found, hone it.





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- If both cylinder block and piston are replaced with new ones, select piston of the same grade number according to the table. These numbers are punched on cylinder block and piston in either Arabic or Roman numerals.





Combination of Trade number for cylinder bore and Piston





3. Measure piston skirt diameter.
Piston diameter "A":
Refer to Engine; Specifications; Mechanical.
Measuring point "a" (Distance from the top): 49.0 mm (1.929 inch)
4. Check that piston-to-bore clearance is within specification.
Piston-to-bore clearance "B":
0.025 - 0.045 mm (0.0010 - 0.0018 inch) for No. 1, 2, and 6 cylinders (and No. 5 cylinder for VG33ER only)
0.015 - 0.025 mm (0.0006 - 0.0010 inch) for No. 3 and 4 cylinders
0.030 - 0.040 mm (0.0012 - 0.0016 inch) for No. 5 cylinder (VG33E only)
5. Determine piston oversize according to amount of cylinder wear.
Oversize pistons are available for service. Refer to Engine; Specifications; Mechanical.
6. Cylinder bore size is determined by adding piston-to-bore clearance to piston diameter "A".
Rebored size calculation:
D = A + B - C where,
D: Bored diameter
A: Piston diameter as measured
B: Piston-to-bore clearance
C: Honing allowance 0.02 mm (0.0008 inch)
7. Install main bearing caps, and tighten to the specified torque to prevent distortion of cylinder bores in final assembly.
8. Cut cylinder bores.
- When any cylinder needs boring, all other cylinders must also be bored.
- Do not cut too much out of cylinder bore at a time. Cut only 0.05 mm (0.0020 inch) or so in diameter at a time.
9. Hone cylinders to obtain specified piston-to-bore clearance.
10. Measure finished cylinder bore for out-of-round and taper.
- Measurement should be done after cylinder bore cools down.