Which combination of instruments is used to measure the fit between a rocker arm shaft and its bushing?

• A. The outside diameter of the shaft is measured with a micrometer caliper, and the inside of the bushing is measured with a telescoping gauge and micrometer caliper.
• B. The inside diameter is measured with a micrometer caliper alone.
• C. The outside diameter is measured with a dial indicator; the inside diameter with a depth gauge.
• D. The inside diameter is measured with a vernier caliper.

Answer: (A)

To determine the fit, you need accurate measurements of both the outside of the rocker arm shaft and the inside of its bushing. The outside diameter of the shaft is measured with a micrometer caliper because it provides a precise external dimension. For the inside diameter of the bushing, a telescoping gauge is used to reach the internal surface and then a micrometer is used to read the exact bore size. This combination gives the true clearance or interference between shaft and bushing, which is essential for a proper fit. Other methods either don’t measure internal diameters with enough precision (such as a dial indicator for size, or a depth gauge) or rely on instruments like vernier calipers that are less accurate for bore measurements.