What kind of measuring instrument is used to measure the runout of an aircraft engine crankshaft?

• A. Depth gauge
• B. Dial indicator
• C. Micrometer
• D. Vernier caliper

Answer: (B)

Measuring runout requires sensing tiny lateral movement of a rotating surface and translating that movement into a readable value. A dial indicator fits this need precisely: its stylus lightly contacts the crankshaft surface and the dial shows even minute deflections as the part rotates. You set the indicator to zero at a reference point, rotate the crankshaft, and read the maximum and minimum indications; the difference between these readings is the runout. This method gives high sensitivity and repeatable results, which is essential for engine crankshafts.

Depth gauges, micrometers, and Vernier calipers aren’t as suitable here. A depth gauge measures how deep a surface is relative to a reference plane, not the lateral wobble of a rotating shaft. A micrometer is great for measuring small dimensions, but it measures fixed thickness or diameter on a stationary part. Vernier calipers can measure external dimensions and some depths, but they don’t provide the continuous, highly sensitive indication of radial deviation needed for accurate runout measurement.