PISTON, PISTON RING, PISTON PIN INSPECTION

Caution

• Do not use a caustic cleaning solution or a wire brush to clean the pistons or damage can occur.

1. Clean and inspect the (1) ring lands, (2) skirts, (3) pin bosses, and the (4) tops of the pistons. If wear marks, scores or glazing is found on the piston skirt, check for a bent or twisted connecting rod.

2. Use the Piston Ring Groove Cleaner to clean the piston ring grooves.

• Make sure the oil ring holes are clean.

Piston outer diameter

Class-1: 84.781-84.799 mm {3.337828-3.338537 in}

Class-2: 85.276-85.294 mm {3.357316-3.3358025 in}

3. Measure the piston dome and skirt diameter 90 degrees from the piston pin at the points indicated.

• If it is out of specification, install new components as necessary.

4. Subtract the piston diameter from the cylinder bore diameter to find the piston-to-cylinder bore clearance.

Maximum clearance

0.05 mm {0.0019685 in}

Note

• The cylinder bore must be within the specifications for taper and out-of-round before fitting a piston.

5. Select a piston size based on the cylinder bore.

Note

• For precision fit, new pistons are divided into three categories within each size range based on their relative position within the range. A paint spot on the new pistons indicates the position within the size range.

6. Choose the piston with the correct paint color.

7. Inspect for a step in the grooves.

8. Measure the piston ring-to-groove clearance.

• If out of specification, install new components as necessary.

Standard clearance

Upper: 1.484 mm {0.058425 in}

Lower: 1.734 mm {0.0682675 in}

Oil control: 2.905 mm {1.1143698 in}

Caution

• Use care when fitting piston rings to avoid possible damage to the piston ring or the cylinder bore.

• Piston rings should not be transferred from one piston to another.

Note

• Cylinder bore must be within specification for taper and out-of-round.

9. Use a piston without rings to push a piston ring in a cylinder to the bottom of ring travel.

10. Use a feeler gauge to measure the top piston ring end gap and the second piston ring end gap.

Standard end gap

Warning

• Cover the end of the pin bore with a hand or shop rag when removing the retainer ring, since it has a tendency to spring out. Wear eye protection.

Note

• Piston and piston pins are a matched set and should not be interchanged.

11. Measure the piston pin bore diameter in two directions on each side. Verify the diameter is within specification.

• If it is out of specification, install new components as necessary.

Standard inner diameter

19.99-20.01 mm {0.7870063-0.7877937 in}

12. Measure the piston pin diameter in two directions at the points shown. Verify the diameter is within specification.

• If out of specification, install new components as necessary.

Standard outer diameter

White: 20.662-20.625 mm {0.8134629-0.8120062 in}

Red: 20.625-20.628 mm {0.8120062-0.8121243 in}

Blue: 20.628-20.631 mm {0.8121243-0.8122424 in}

13. Calculate the clearance between the piston pin hole diameter and the piston pin outer diameter.

• If not within the specification, replace the piston or the piston pin.

Standard clearance

0.010-0.015 mm {0.0003937-0.0005905 in}