39. Piston, Connecting Rod, and Bearing Clean and Inspect
Piston, Connecting Rod, and Bearings Cleaning and Inspection
1. Important: Inspect the piston, pin and connecting rod with the components at room temperature. Do not use a wire brush to clean the piston ring grooves. Do not cut the ring grooves deeper with a groove cleaning tool.
Inspect the piston for the following conditions:
^ Distortion or cracking
^ Eroded areas (1) at the top of the piston
^ Scuffed or damaged skirt (2)
^ Scoring to the piston pin bore (3)
2. Inspect the connecting rod for the following conditions:
^ Twisting (2)
^ Nicks or gouging in the pin or bearing bores (1 and 3)
^ Proper fit of the connecting rod and cap (4)
3. Clean all the piston ring grooves thoroughly with a ring groove cleaning tool.
4. Measure the piston diameter at a point 16 mm (0.63 inch) from the bottom of the skirt (a).
^ Piston diameter - new: 88.975 - 88.985 mm (3.5029 - 3.5033 inch)
^ Piston diameter - service limit: 88.965 mm (3.5026 inch)
^ 0.25 mm (0.0098 inch) oversize piston diameter: 89.225 - 89.235 mm (3.5128 - 3.5132 inch)
5. Measure the piston pin diameter.
^ Piston pin diameter - new: 21.962 - 21.965 mm (0.8646 - 0.8648 inch)
^ Piston pin diameter - service: 21.954 mm (0.8643 inch)
6. Measure the piston pin bore.
7. Calculate the pin-to-bore clearance.
^ Piston pin-to-bore clearance - new: -0.005 to +0.001 mm (-0.0002 to +0.00004 inch)
^ Piston pin-to-bore clearance - service limit: 0.004 mm (0.0002 inch)
8. Measure the connecting rod pin bore.
9. Calculate the piston pin-to-connecting rod clearance.
^ Piston pin-to-connecting rod clearance - new: 0.005 - 0.014 mm (0.0002 - 0.0006 inch)
^ Piston pin-to-connecting rod clearance - service limit: 0.019 mm (0.0007 inch)
Connecting Rod Bolt Inspection
1. Measure the diameter of each connecting rod bolt at the 2 measurement points (1 and 2) - 35 mm (1.38 inch) (a) and 20 mm (0.79 inch) (b).
2. Calculate the difference between the 2 measurements. If the difference between the 2 measurements exceeds the specification, replace the bolt.
Connecting rod bolt - difference in diameter: 0.0 - 0.1 mm (0.0 - 0.004 inch)
Piston Selection
1. Measure the piston diameter.
2. Measure the cylinder bore diameter.
3. Calculate the clearance between the piston and the cylinder bore.
^ Piston-to-bore clearance - new: 0.015 - 0.04 mm (0.0006 - 0.0016 inch)
^ Piston-to-bore clearance - service limit: 0.08 mm (0.003 inch)
4. A 0.25 mm (0.010 inch) oversize piston can be identified by the numbers 25 on the top of the piston.
Piston Ring Selection
1. Insert the piston ring (122) into the cylinder 15 - 20 mm (0.6 - 0.8 inch) (a) from the bottom of the bore.
2. Measure the piston ring end gap (b) with a feeler gage.
1 If the gap is too small, check to see if you have the proper rings for the application.
2 If the gap is too large, check the cylinder bore diameter against the wear limits.
3 If the bore diameter exceeds the service limit, the cylinder block must be bored and fitted with oversize pistons and piston rings.
^ Piston ring end gap - top ring - production: 0.2 - 0.35 mm (0.008 - 0.014 inch)
^ Piston ring end gap - second ring - production: 0.4 - 0.55 mm (0.016 - 0.022 inch)
^ Piston ring end gap - oil ring - production: 0.2 - 0.7 mm (0.008 - 0.028 inch)
^ Piston ring end gap - top ring - service limit: 0.6 mm (0.024 inch)
^ Piston ring end gap - second ring - service limit: 0.7 mm (0.028 inch)
^ Piston ring end gap - oil ring - service limit: 0.8 mm (0.031 inch)