Which of the following tools is recommended for checking cylinder block line bore?

The master line bore bar is the recommended tool for checking cylinder block line bore due to its ability to provide precise measurements of the alignment and diameter of the cylinder bore. This tool is specifically designed to ensure that the bores are aligned correctly over the length of the cylinder block, which is crucial for optimal engine performance.

The master line bore bar incorporates a length adjustment feature and can typically be used in conjunction with dial indicators or other measuring instruments to check for any misalignment. This precision is important because even minor misalignments can lead to excessive wear on engine components, improper sealing, or even engine failure.

While other tools like a dial bore gauge are also valuable for measuring bore diameters and ensuring they meet specifications, they do not specifically address alignment across the entire cylinder block as thoroughly as a master line bore bar does. A straightedge and thickness gauges can help in some general alignment checks, but they lack the precision required for detailed line bore measurements. Similarly, a dial indicator is used for different types of measurements and would not provide the comprehensive data needed for assessing line bore.