Workshop Measurement, Servicing and Preventive Maintenance
This domain tests measuring instruments to the correct least count, servicing routines and the preventive maintenance schedule that keeps a vehicle reliable.
Measuring instruments
A steel rule reads to about 0.5 mm. A vernier caliper typically has a least count of 0.02 mm, found as 1 main scale division minus 1 vernier scale division. An outside micrometer has a least count equal to the screw pitch divided by the number of thimble divisions, commonly 0.5 mm divided by 50, which is 0.01 mm. A dial gauge reads 0.01 mm and is used for crankshaft end play, runout and gear backlash. A feeler gauge sets tappet clearances and spark plug gaps, a bore gauge measures cylinder wear, and a plastigauge checks bearing oil clearance. A compression gauge diagnoses poor sealing and a hydrometer checks battery state of charge. Always check zero error before use and clean the instrument after use.
Servicing and preventive maintenance
Daily checks: engine oil level, coolant, brake fluid, tyre pressures and condition, lights, horn and wipers, plus any leaks under the vehicle. Periodic services at set kilometre intervals include engine oil and filter renewal, air and fuel filter cleaning or replacement, greasing of joints, checking belt tension, battery terminals, brake shoe and pad condition, clutch pedal free play, wheel bearing play, wheel alignment and tyre rotation. Decarbonising, tappet adjustment and ignition timing are done during tune-ups. Preventive maintenance reduces breakdowns and is cheaper than breakdown repair.
Worked example
A vernier caliper shows the zero of the vernier scale past the 12 mm main scale mark, and the 24th vernier division is coincident with a main scale line. Reading = 12 + (24 x 0.02) = 12.48 mm.
Traps that cost marks
Forgetting the zero error correction; reading the thimble on a micrometer in the wrong direction; measuring a hot engine part; using a burred feeler gauge; over-tightening a sump drain plug; ignoring scheduled greasing.