Piston

Pistons
Carefully clean away all the carbon adhering to the piston head and the piston ring grooves.

Note: Never use a wire brush to clean the pistons. Damage will result. Visually check each piston for cracking, scoring, and other signs of excessive wear. If any of the above conditions are found, the piston must be replaced.

Piston Diameter





1. Measure the piston outside diameter with micrometer at the piston grading position and a right angle to the piston pin.
Piston grading position (from piston head)
Piston grading position: 43.0 mm (1.6929 inch)





The size mark (1) for piston outside diameter is represented as shown in illustration.
Outside Diameter
Size Mark A: 93.360 mm - 93.370 mm (3.6756 inch - 3.6760 inch)
Size Mark B: 93.371 mm - 93.380 mm (3.6760 inch - 3.6764 inch)
Size Mark C: 93.381 mm - 93.390 mm (3.6764 inch - 3.6768 inch)





2. Measure the cylinder bore inside diameter.

Piston Rings
Any worn or damaged part discovered during engine overhaul must be replaced with a new one.





1. Ring end gap measurement





^ Insert the piston ring into the bore.
^ Push the ring by the piston, at a right angle to the wall, into the point at which the cylinder bore diameter is the smallest.
^ Measure the ring end gap.





^ Positioning mark (1) is painted as shown in the illustration.
Marked T: No.1 Compression ring
Marked T2: No.2 Compression ring





2. Measure the clearance between the piston ring groove and the piston ring with a feeler gauge. If the piston ring groove/piston ring clearance exceeds the specified limit, the piston must be replaced.
Compression Ring Clearance
Standard: 0.016 mm - 0.038 mm (0.0006 inch - 0.0015 inch)
Limit: 0.15 mm (0.0059 inch)

Piston Pin

Note: Do not reuse the old piston pin.

1. Use a micrometer to measure the new piston pin outside diameter in both directions at three different positions.





2. Measure the inside diameter of the connecting rod small end. If the fitting interference between the small end and pin does not conform to the specified value, the connecting rod must be replaced.
Standard: 0.023 mm - 0.038 mm (0.0009 inch - 0.0015 inch)
3. Insert the new pin into the piston and rotate it. If the pin rotates smoothly with no backlash, the clearance is normal. If there is backlash or roughness, measure the clearance. If the clearance exceeds the specified limit, the piston must be replaced.
Clearance
Standard: 0.010 mm - 0.017 mm (0.0004 inch - 0.0007 inch)
Limit: 0.040 mm (0.0016 inch)