How is cylinder bore out-of-round and taper measured during overhaul?

How is cylinder bore out-of-round and taper measured during overhaul?

• A. With a calibrated dial bore gauge or equivalent instrument at multiple positions to determine taper and out-of-round within the spec.
• B. By measuring the bore with a ruler at a single point around the circumference.
• C. By measuring piston ring end gaps while the bore is cool.
• D. Using a single-point micrometer in one location only.

Answer: (A)

Precise bore geometry is determined by checking diameter at multiple angular positions along the bore and at several depths using a calibrated dial bore gauge (or an equivalent instrument). This approach reveals both taper (diameter change along the bore length) and out-of-round (ovality around the circumference). You set the gauge to the reference size, insert it into the bore, and take readings at several axial locations (top, mid, bottom) and at different around-the-bore angles (for example, every 90 degrees). The largest and smallest readings around a given plane show out-of-round, while the difference between top and bottom diameters shows taper. All measurements must be compared to the engine’s specified limits. Using a ruler at a single point won’t reveal ovality, measuring piston ring end gaps isn’t about bore shape, and a single-point micrometer doesn’t capture the full variation, so it wouldn’t provide an accurate picture of bore condition.

Precise bore geometry is determined by checking diameter at multiple angular positions along the bore and at several depths using a calibrated dial bore gauge (or an equivalent instrument). This approach reveals both taper (diameter change along the bore length) and out-of-round (ovality around the circumference). You set the gauge to the reference size, insert it into the bore, and take readings at several axial locations (top, mid, bottom) and at different around-the-bore angles (for example, every 90 degrees). The largest and smallest readings around a given plane show out-of-round, while the difference between top and bottom diameters shows taper. All measurements must be compared to the engine’s specified limits. Using a ruler at a single point won’t reveal ovality, measuring piston ring end gaps isn’t about bore shape, and a single-point micrometer doesn’t capture the full variation, so it wouldn’t provide an accurate picture of bore condition.