Use Hand Tools, Measuring Instruments, and Servicing Equipment
Hand Tools, Measuring Instruments, and Servicing Equipment
This domain tests tool selection, correct use, care, and accurate measurement. Questions often ask which instrument suits a particular check and what error spoils a reading.
Core rules
- Use the right size: a 12 mm box wrench on a 12 mm hex. An adjustable wrench rounds nuts when torque is high.
- Pull a wrench toward you with an open palm; never push, and never extend a wrench with a pipe - you lose torque feel and can snap the fastener.
- Torque wrench: set to spec, tighten smoothly until the click, and reset to the lowest setting before storage so the spring does not take a set.
- Spread cylinder-head bolts in a crisscross pattern in two or three stages to the manual's final torque.
- Vernier caliper least count 0.02 mm; outside micrometer 0.01 mm; feeler gauge for gaps; cylinder bore gauge for taper and out-of-round; dial indicator for runout; compression gauge for cylinder sealing; multimeter for volts, ohms, and continuity.
- Wipe measuring faces, zero the instrument, read at eye level to avoid parallax, and measure at room temperature.
Worked example
A cylinder's service limit is 52.00 mm. The bore gauge is zeroed on a 52.00 mm micrometer, then read at top, middle, and bottom on two axes: 51.98, 52.01, and 52.02 mm. The maximum is inside the limit, but taper (52.02 − 51.98 = 0.04 mm) is close to the 0.05 mm limit, so the technician recommends re-boring at the next service. Reasoning: judge both absolute diameter and taper/out-of-round, because a cylinder can pass on size and fail on shape.
Traps
Reading the wrong vernier scale; measuring a hot engine; forcing a feeler gauge instead of letting a "go" gauge slide with light drag; torqueing dry when the specification is for oiled threads, which changes the real clamp load.