33. Piston, Connecting Rod. and Bearings Clean and Inspect
Piston and PinImportant: Replace the pistons and the pins that are damaged or show signs of excessive wear.
The piston and the pin are a matched set. If service is required, replace the piston and the pin as an assembly.
Do not wire brush any part of the piston.
1. Clean the varnish from the piston and the pin with cleaning solvent.
2. Dry the piston and the pin with compressed air.
3. Clean the piston ring grooves with a suitable ring groove cleaning tool.
4. Clean the oil lubrication holes and slots.
5. Inspect the piston and the pin for the following:
^ Cracks in the piston ring lands, the piston skirt, or the pin bosses
^ Piston ring grooves for nicks, burrs, or warpage which may cause the piston ring to bind
MINOR imperfections may be removed from the piston with a fine file.
^ Scuffed or damaged skirts (2)
^ Eroded areas at the top of the piston (1)
^ Scoring to the piston pin bore (3) or the piston pin
Important: Measurements of components should be taken with the components at normal room temperature.
6. Measure the piston ring-to-piston ring groove side clearance.
6.1. Insert the edge of the piston ring into the piston ring groove.
6.2. Roll the piston ring completely around the piston.
^ If binding is caused by a distorted piston ring groove, MINOR ring groove imperfections may be removed with a fine file.
^ If binding is caused by a distorted piston ring, replace the piston ring.
7. Measure the piston ring side clearance with a feeler gauge.
8. If side clearance is not within specifications, try another piston ring set.
9. The proper piston ring-to-piston ring groove side clearance is:
^ The top compression ring side clearance is 0.04 - 0.085 mm (0.00157-0.003346 inch).
^ The second compression ring side clearance is 0.04 - 0.08 mm (0.00157 - 0.003149 inch).
^ The oil control ring side clearance is 0.01 - 0.22 mm (0.0004 - 0.00866 inch).
10. If proper piston ring-to-piston ring groove side clearance cannot be achieved, replace the piston and pin assembly.
11. To determine piston pin-to-bore clearance, use a micrometer and measure the piston pin.
12. To determine piston pin-to-bore clearance, use an inside micrometer and measure the piston pin bore.
Important: The piston and pin are a matched set. If the clearance is not within specifications, replace the piston and pin as an assembly.
13. To determine the proper piston pin-to-bore clearance, subtract the piston pin diameter from the piston pin bore diameter.
The proper piston pin-to-bore clearance is 0.012 - 0.024 mm (0.0004 - 0.0009 inch).
14. Measure the piston for out-of-round.
14.1. With the micrometer at a right angle to the piston, measure the 5.3/6.0 cast dome piston at 0.10 mm (0.4 inch) from the bottom of the skirt.
The cast dome piston can be identified by the rough finish surface (with recessed center area) on the top of the piston.
14.2. With the micrometer at a right angle to the piston, measure the 4.8/6.0 machined dome piston 0.15 mm (0.6 inch) from the bottom of the skirt.
The machined dome piston can be identified by the machined, smooth, flat surface (no recess) on the top of the piston.
14.3. Measure the piston at two different points and compare the readings.
14.4. If the piston is more than 0.018 mm (0.0007 inch) out-of-round, replace the piston and pin as an assembly.
Connecting Rod and Bearings
Important: The powdered metal connecting rod and cap are machined for the proper clearances. The connecting rod and the cap must be used as an assembly with no repair or modifications to either mating surface.
Do not attempt to repair the connecting rod or the cap mating surfaces. If service is required, the connecting rod and the cap must be replaced as an assembly.
1. Clean the connecting rod and the cap in solvent.
Important: Replace the connecting rod if the bolt hole threads are damaged. Do not attempt to repair the bolt hole threads of the connecting rod.
2. Clean the connecting rod threaded bolts holes.
Caution: Wear safety glasses in order to avoid eye damage.
3. Dry the connecting rod with compressed air.
4. Inspect the connecting rod for the following:
^ Twisting
^Nicks or gouging in the bearing bore
^ Damage to the bearing locating slots in the bearing bore
^ Proper fit of the connecting rod and the cap mating surfaces
5. Measure the connecting rod bearing bore for out-of-round.
If the measurement exceeds 0.008 mm (0.0003 inch), replace the connecting rod assembly.
6. Inspect the connecting rod bearings for craters or pockets. Flattened sections on the bearing halves also indicate fatigue.
7. Inspect the connecting rod bearings for excessive scoring or discoloration.
8. Inspect the connecting rod bearings for dirt or debris imbedded into the bearing material.
9. Inspect the connecting rod bearings for improper seating indicated by bright, polished sections of the bearing.
Measuring Piston Ring End Gap
Important: Do not attempt to file the end of the piston ring for fit in the cylinder bore.
Important: Measure the piston ring in the cylinder in which the piston ring will be used.
1. Place the piston ring into the cylinder bore.
2. Push the piston ring into the bore 6.5 mm (0.25 inch) below the piston ring travel area.
3. Insert a feeler gauge and measure the piston ring end gap. Refer to Specifications.