EL-740 Air Compressor Inspection – Pistons, Connecting Rods And Bearings

1. Examine the pistons for scoring, nicks, burrs, cracks, or other damage. Replace, as needed.

2. Measure the outside diameter of the piston at a 90 degree angle to the piston pin bore. Compare this measurement with the diameter of the cylinder bore. Piston to cylinder bore clearance should not exceed 0.20 mm (.008 in). If clearance exceeds 0.20 mm (.008 in), replace the pistons. The cylinder block must be replaced or bored oversize 0.25 mm (.010 in) or 0.50 mm (.020 in). Oversize pistons 0.25 mm (.010 in) or 0.50 mm (.020 in) and oversize piston ring sets are available.

NOTE: Oversize pistons and rings must be used in conjunction with oversize cylinder bores. When measuring the outside diameter of the piston the micrometer must be at a 90 degree angle to the piston pin bore. This will permit a correct measurement.

3. Check the fit of the piston pin in the piston and connecting rod. The piston pin must have a light interference fit in the piston and a slip fit in the connecting rod. Determine which part or parts are worn and replace as required. The connecting rod and connecting rod cap must be replaced as a unit.

4. Check the fit of the compression and oil rings in the piston ring grooves. The oil rings must move freely on the piston. Place the oil rings in the cylinder bores and measure the ring gap. If the ring gaps are not within the limits of the “Specifications” section, new oil rings must be installed.

NOTE: When new oil rings are used, cylinder bores should be re-honed.

5. Examine the connecting rod bearing inserts for scoring, pitting or visible wear. Check the fit of the connecting rod bearings on the crankshaft journals. Clearance between the rod bearings and the crankshaft journal must be between 0.013 mm (.0005 in) and 0.053 mm (.0021 in). If damage is evident or clearance does not meet the specified dimensions, new rod bearing inserts must be installed.

6. Check the clearance between the side of the connecting rod and the crankshaft. If clearance exceeds 0.254 mm (.0100 in), a new connecting rod assembly must be installed.

NOTE: The connecting rod and connecting rod cap must be replaced as a unit.

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