In an internal combustion engine, a barring adapter member is mounted on an auxiliary engine component, such as an air compressor shaft which is geared to the engine crankshaft. The barring adapter member is configured to receive a barring tool, permitting manual rotation of the air compressor shaft for desirably positioning engine crankshaft-driven components during engine repair or adjustment. In an arrangement according to the invention, the air compressor gear is enclosed by a gear casing, but the adapter is accessible through an aperture closeable by a removable cap. The barring adapter member facilitates barring the engine from a convenient position and is particularly advantageous in an engine designed to eliminate most externally-exposed rotational shaft seals and associated external pulleys conventionally used as barring locations.