Reciprocating Engine Construction and Operation
Core concepts
Know the major components and their functions: crankcase, crankshaft, connecting rods, pistons, cylinders, cylinder heads, valves, camshaft, valve train, and accessory housing. Understand cylinder arrangements (horizontally opposed, radial, in-line, V), cooling fin design, and the difference between direct-drive and geared engines. Learn valve timing, valve clearance, and how hydraulic lifters work. Understand firing order, crankshaft counterweights, and balance. Study ignition timing relative to top dead center, valve overlap, and the purpose of the compression stroke. Be able to explain why air-cooled cylinders need baffles and how detonation and preignition differ.
Traps to expect
Questions frequently confuse detonation (uncontrolled rapid burn after normal ignition) with preignition (ignition before the spark, often from a hot spot). Another trap is valve clearance: too little clearance can hold a valve off its seat; too much causes noise and reduced lift. Do not confuse valve lead, lag, and overlap. Radial engines have an odd number of cylinders per row to smooth firing; know why. Also know that a broken ring, scored cylinder, or stuck valve produces specific symptoms (oil consumption, low compression, rough running).
Worked example
A four-cylinder engine fires once per cylinder per two revolutions, so total power strokes per revolution equal half the cylinder count: 4/2 = 2 power strokes per revolution. Rule of thumb: power strokes per revolution = number of cylinders ÷ 2 for a four-stroke engine.
Study habit
Sketch a cylinder and label intake, compression, power, and exhaust events with crank angles. Being able to draw valve events makes timing questions much easier.