Spark

Piston, Connecting Rod, and Bearing Cleaning and Inspection

Connecting Rod

Warning: Refer to Safety Glasses Warning in the Preface section.




1. Clean the connecting rods in solvent and dry with compressed air.
2. Inspect the connecting rod for the following:

•	Signs of being twisted, bent, nicked or cracked

•	Scratches or abrasion on the connecting rod bearing seating surfaces

Piston

1. Clean the piston with a cleaning solvent. DO NOT wire brush any parts of the piston.
2. Clean the piston ring grooves.
3. Inspect the piston on the following:

•	Cracked ring lands, skirts or pin bosses

•	Ring grooves for nicks

•	Eroded areas on the top of the piston (1)

•	Scuffed or damaged skirts (2)

•	Worn gudgeon pin bores (3)

4. If there is any excessive wear, replace the piston.
5. Measure the clearance between piston pin and piston bore. Use the following procedure:

Piston Pin To Connecting Rod Bore And Piston Bore Clearance

1. Measure clearance between piston pin and connecting rod bore. Use the following procedure:

1.1.	Measure the piston pin outside diameter.

1.2.	Measure the connecting rod bore diameter.

1.3.	Subtract the piston ring diameter from the connecting rod diameter.

1.4.	Refer to Engine Mechanical Specifications to find the permitted values.

2. If there is excessive clearance, replace the gudgeon pin.
3. If there is still excessive clearance, replace the connecting rod.

3.1.	Measure the piston pin outside diameter.

3.2.	Measure the piston bore diameter.

3.3.	Subtract the piston pin diameter from the piston bore diameter.

3.4.	Refer to Engine Mechanical Specifications to find the permitted values.

4. If there is excessive clearance, replace the gudgeon pin.
5. If there is still excessive clearance, replace the piston.

Piston Ring Clearance

1. Install the piston rings to the cylinder as shown and measure the piston ring end gap. Compare the measurements with those provided below:

•	The upper compression ring end gap. Refer to Engine Mechanical Specifications to find the permitted values.

•	The lower compression ring end gap. Refer to Engine Mechanical Specifications to find the permitted values.

•	The oil ring end gap. Refer to Engine Mechanical Specifications to find the permitted values.

2. If the clearance is greater than the provided specifications, the piston rings must be replaced.



3. Measure the piston ring side clearance as shown. Compare the measurements with those provided below:

•	The upper compression ring side clearance. Refer to Engine Mechanical Specifications to find the permitted values.

•	The lower compression ring side clearance. Refer to Engine Mechanical Specifications to find the permitted values.

•	The oil ring side clearance. Refer to Engine Mechanical Specifications to find the permitted values.

4. If the clearance is greater than the provided specifications, replace the piston rings.
5. If the clearance is still to great, replace the pistons.

Connecting Rod Bearing Clearance (With Micrometer Gauge Internal Measuring Device)

1. Install the connecting bearings and the connecting rod bearing caps.
2. Tighten the connecting rod bearing cap bolts in the following sequence:

Caution: Refer to Fastener Caution in the Preface section.

Note: The old bolts can be reused for the measuring procedure.

2.1.	Tighten the connecting rod bearing cap bolts to 20N·m(15 lb ft).

2.2.	Tighten the bolts to an additional 40°.




3. Measure the connecting rod bearing diameters at 3 points as shown (1). Use an internal measuring device.
4. Calculate the average connecting rod inner diameter.

Formula: 1.result + 2. result + 3. result / 3




5. Measure the connecting rod journal diameter at 2 points between 1 and 3 and between 2 and 4. Use a micrometer gauge.
6. Calculate the average connecting rod journal diameter.

Formula: 1. result + 2. result / 2.

7. Subtract the average connecting rod journal diameter from the average connecting rod bearing diameter in order to determine the connecting rod bearing clearance.

Refer to Engine Mechanical Specifications to find the permitted values.