Engineering Materials
What this domain tests
The paper tests ferrous and non-ferrous metals, carbon percentage in steels, cast iron, aluminium alloys, bearing and gasket materials, plastics, rubber and heat treatment. Questions link material properties to motorcycle components and failure modes.
Core rules
- Mild steel contains roughly 0.05–0.30% carbon, medium-carbon steel 0.30–0.60% and high-carbon steel 0.60–1.40%. Higher carbon raises hardness and wear resistance but lowers ductility and weldability.
- Cast iron contains about 2–4% carbon and is brittle in tension but good in compression and damping.
- Aluminium alloys give low weight and good heat conduction; pistons are commonly aluminium-silicon alloys running in iron or plated liners.
- Annealing softens and relieves stress; normalising refines grain; hardening followed by tempering trades some hardness for toughness.
- Bearing shells use soft overlay materials so embedded dirt does not score the crankshaft.
- Gasket materials must suit the fluid, temperature and clamping load; rubber seals need clean, dry seats and correct preload.
Worked example
A cylinder bore measures 57.00 mm and the piston skirt measures 56.95 mm. Piston-to-bore clearance = 57.00 − 56.95 = 0.05 mm. If the specification is 0.04–0.06 mm, the fit is acceptable. Re-boring without matching an oversize piston would destroy this clearance.
Traps that cost marks
Assuming hardening alone is sufficient without tempering; using mild steel for a high-stress fastener; fitting a gasket with sealant where the manufacturer specifies dry assembly; confusing hardness with toughness.
Key points
- Carbon content controls steel hardness and ductility.
- Cast iron is strong in compression, weak in tension.
- Aluminium pistons need controlled cold clearance.
- Harden then temper for usable toughness.
- Gasket material must match fluid and temperature.