1. Ready for Review

WRAP UP: 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.

 

©2026 - CDX