Chapter 05: Final Review & Key Terms

1. Ready for Review

• Efficient and reliable engine operation depends on the use of precision-machined parts correctly assembled to function together.
• Accurate control of dimensions for engine components is also necessary to enable components to be used interchangeably.
• Precision measurement and machining generally refer to dimensional control of parts and components in the thousandths of inches or millimeters.
• Precision measuring tools take more accurate measurements of components beyond the capabilities of ordinary, non-precision measuring instruments such as tape measures and rulers.
• Precision measuring instruments measure components to determine their serviceability —a term describing the process of inspecting and evaluating a part to make a correct recommendation for replacement, repair, or return of a component to service as it is.
• Precision measuring tools have been developed to compensate for the inaccurate estimation of linear distances, clearances, or thicknesses by using line-graduated measuring tools (such as rulers or measuring tapes) or dependence on the sense of sight and touch to take measurements.
• Production, replacement, and inspection of engine components rely on clearly established standards of measurement to accurately identify or verify a dimension.
• Component sizes and clearances are commonly measured using metric or SI measuring units and the U.S. System of Weights and Measurement established by the U.S. National Bureau of Standards.
• The U.S. system, sometimes called by the longer, more technical term, U.S. Customary System (USCS) , is loosely based on British or Imperial Weights and Measures.
• The ISO, which establishes measurement standards for technology used by commercial vehicles, aircraft, off-road equipment, and automobiles, uses the SI system for measuring units.
• In the U.S., the SAE is the organizational equivalent to the ISO that establishes vehicle engineering standards and has historically incorporated the USCS of measurement.
• Linear-type measurements involve measurements of length, which is the straight-line distance between two points.
• Various types of calipers are frequently used measuring tools to make linear measurements of outside, inside, and depth dimensions.
• Vernier calipers are a type of sliding caliper that make more precise measurements than a simple sliding caliper with a single main graduated scale.
• Measuring tools with higher resolution means a smaller, more accurate measurement is made having more significant digits or numbers.
• Vernier scales are also on micrometers and other measuring tools to enable a device to achieve extra decimal points in its measurement resolution.
• Micrometers are used to take more accurate measurements than a vernier-type sliding caliper.
• Micrometers can measure inside, outside, or depth.
• A depth micrometer reverses the order of the numbers on the sleeve. As the spindle extends from the micrometer, the numbers uncovered by the thimble will increase.
• Telescoping gauges are linear measuring devices that can measure holes or internal diameters. These devices are used with micrometers, which make the final numerical measurement.
• Feeler gauges, also commonly called thickness gauges , are linear measuring tools used to precisely measure the dimensions of small gaps or between two parts.
• Feeler gauge blades are available in various lengths and may be flat or bent at an angle to enable them to be more easily used for a specific purpose.
• Gauge blocks are precision-machined pieces of aluminum or steel for determining whether a dimension’s thickness or width is within specification.
• Dial indicators are one of the most versatile precision measuring tools used due to their measuring speed, ease of use, and accuracy. The indicator converts linear movement of a plunger to rotational movement of a dial pointer.
• To obtain lengthier measurements of dimensions, a dial indicator can be constructed with a second, smaller pointer on the dial face that counts the revolutions of the larger dial pointer.
• Most dial indicators are a balanced gauge type, which can measure plunger movement in two directions.
• Measuring concentricity of an object involves determining how closely a circular object is centered around its axis. A nonconcentric object will have lateral runout from its centerline axis.
• Machine fits refer to the clearances between the contact surfaces of parts.

2. Key Terms

catastrophic failure Defined as a direct failure damaging more than 50% of engine parts or consequential damage resulting from a failure.

measuring units Units that follow a numerical measurement and provide information about the measurement quantity.

resolution Measuring devices with higher resolution means a smaller, more accurate measurement is made having more significant digits or numbers.

serviceability A term describing the process of inspecting and evaluating a part to make a correct recommendation for replacement, repair, or return of a component to service as it is.

Systems International (SI) System The technical name that sets standards for metric-based measurement.

U.S. Customary System (USCS) The U.S. system of weights and measurement was established by the U.S. National Bureau of Standards. This U.S. system is loosely based on British or Imperial Weights and Measures.