Piston-to-Bore Clearance

PISTON-TO-BORE CLEARANCE





1. Using a bore gauge, measure cylinder bore for wear, out-of-round and taper. The Y axis is in the longitudinal direction of the engine.
Standard inner diameter (Grade No. 1): 80.000 - 80.010 mm (3.1496 - 3.1500 inch)
Wear limit: 0.2 mm (0.008 inch)
Out-of-round (X - Y) standard: Less than 0.015 mm (0.0006 inch)
Taper (B - A) standard: Less than 0.01 mm (0.0004 inch)
If it exceeds the limit, rebore all cylinders. Replace cylinder block if necessary.





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

NOTE: If cylinder block or piston is replaced, match piston grade with grade number on cylinder block lower surface.





3. Measure piston skirt diameter.
Piston diameter A: Refer to Piston, Piston Ring and Piston Pin.
Measuring point a (Distance from the top): 42.3 mm (1.665 inch)
4. Check that piston-to-bore clearance is within specification.
Piston-to-bore clearance = cylinder bore measurement B - Piston diameter A: 0.025 - 0.045 mm (0.0010 - 0.0018 inch)
5. Determine piston oversize according to amount of cylinder wear.
^ Oversize pistons are available for service. Refer to Piston, Piston Ring and Piston Pin.
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 bolts to the specified torque. This will prevent distortion of cylinder bores.
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 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.