Piston to Bore - Clearance

PISTON-TO-BORE CLEARANCE
1. Using a bore gauge, measure cylinder bore for wear, out-of-round and taper.






If it exceeds the limit, rebore all cylinders. Replace cylinder block if necessary.

Out-of-round (X - Y): Limit ...........0.015 mm (0.0006 inch)
Taper (A - B - C): Limit ..............0.015 mm (0.0006 inch)

2. Check for scratches and seizure. If seizure is found, hone it.






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






3. Measure piston skirt diameter.

Measuring point "a" (Distance from the top): ............41.0 mm (1.61 inch)

4. Check that piston-to-bore clearance is within specification.

Piston-to-bore clearance "B": ............0.010 - 0.030 mm (0.0004 - 0.0012 inch)

5. Determine piston oversize according to amount of cylinder wear. Oversize pistons are available for service.

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. Otherwise, cylinder bores may be distorted 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.