Piston and Engine Component Verification: A Detailed Inspection

Piston Verification: Ensuring Optimal Engine Performance

Checking Piston Sliding Zones

Inspect the sliding zones of the piston. There should be no signs of jamming or excessive friction.

Weight Difference Between Pistons

Use a balance to compare the weight of each piston. Differences up to 4 grams are allowed. Larger differences can cause crankshaft imbalance and vibrations.

Piston Diameter

Pistons are not perfectly cylindrical. Follow the manufacturer's instructions to measure the diameter at the specified zone, usually at a certain distance from the head, measured transversally at the same height as the bolt. The installation clearance between the piston and cylinder compensates for thermal expansion and is typically between 0.02 and 0.05 mm.

Bolt Diameter

Measure the bolt diameter with a micrometer and check for streaks or signs of wear.

Piston Pin Bore Diameter

Measure the piston pin bore diameter longitudinally and transversely with an inside micrometer to detect possible ovality.

Calculate Mounting Clearance

Determine the difference in diameter between the bolt and its bore.

Segment Verification

• Measure the thickness of each segment: Use a micrometer to check for wear.
• Check the opening between points: Insert the segment into the cylinder and push it with the piston head to achieve a horizontal position. Measure the gap with a feeler gauge.
• Check the axial clearance of the segment in its housing: Mount the segments in their slots and measure the clearance with a feeler gauge.

Verifying Connecting Rods

Weight Difference Between Connecting Rods

The maximum weight difference between connecting rods, including bearings, should not exceed 6 grams.

Alignment of Connecting Rod Axes

Insert the pin into the small end of the connecting rod and mount it on a testing device. Verify the parallelism between axes and check for possible torsion.

Small End Bearing Ovality

Measure the small end bearing with an inside micrometer in transverse and longitudinal directions to calculate ovality. Calculate the mounting clearance with the bolt diameters. Verify that the bearing has not shifted and that the oil holes are aligned.

Big End Bearing Ovality

Fit the bearing shells in position, mount the cap, and tighten it to the specified torque. This ensures that the bearing shells are firmly seated. Measure the longitudinal and transverse diameters with an inside micrometer. The ovality is the difference between these two diameters, with a maximum of 0.03 mm.

Crankshaft Verification

Eccentricity of the Central Support

Use a dial indicator to check the central support while rotating the crankshaft on a V-block. The maximum deviation of the needle should not exceed 0.04 mm. Check the condition of the journals and supports.

Journal and Support Ovality

Measure perpendicularly with a micrometer. The ovality should not exceed 0.04 mm.

Journal and Support Taper

Measure the diameter at the ends of each journal and support with a micrometer. The taper should not exceed 0.03 mm.

Journal Assembly Clearance, Support Mounting Clearance

The assembly clearance for the journals and their respective supports should be between 0.02 and 0.06 mm, and should not exceed 0.15 mm.

Flywheel Verification

Flywheel Runout

Place a dial indicator in contact with the plane of the flywheel in its peripheral area. Rotate the flywheel and check that the maximum runout does not exceed 0.06 mm.

Engine Block Verification

Check the Upper Plane of the Block

Use a straightedge and a feeler gauge to check the upper plane in longitudinal and transverse positions. Use a 0.05 mm feeler gauge.

Main Bearing Ovality

Place the bearing shells, install the caps, and tighten them to the specified torque. Measure the horizontal and vertical diameters with an inside micrometer (maximum 0.04 mm).