100+ Free SACAA AME Engines Practice Questions

Explanation: A four-stroke engine operating on the Otto cycle requires four distinct piston strokes (intake, compression, power, and exhaust). Each stroke corresponds to 180 degrees of crankshaft rotation. Therefore, 4 strokes × 180° = 720° of total crankshaft rotation (or two complete revolutions) to execute the complete thermodynamic cycle.

Explanation: Valve overlap is the period near Top Dead Center (TDC) end of the exhaust stroke / start of intake stroke when both intake and exhaust valves are open simultaneously. The rapid velocity of exiting exhaust gases creates a low-pressure area in the cylinder, helping scavenge remaining burned gases while pulling in the fresh intake air-fuel mixture, thereby improving volumetric efficiency and cylinder cooling.

Explanation: Nitriding is a surface hardening process in which the steel cylinder barrel is heated in an atmosphere of ammonia gas (nitrogen compounds). Nitrogen reacts with alloy elements in the steel to form micro-hard nitrides on the cylinder wall, creating a highly wear-resistant surface while maintaining the ductility and toughness of the underlying steel core.

Explanation: The oil control ring is positioned below the compression rings. Its primary duty is to wipe excess lubricating oil from the cylinder walls during piston downstrokes and return it to the crankcase through relief oil holes in the piston ring groove, leaving only a microscopic oil film necessary for lubrication.

Explanation: Dynamic counterweights act as unguided pendulums attached to crankshaft crank cheeks. They oscillate at specific frequencies tuned to counter the torsional vibrations produced by power impulses from individual cylinders, preventing crankshaft fatigue failure caused by critical speed resonance.

Explanation: Radial engines utilize a master-and-articulated connecting rod assembly. The master rod directly connects one piston (master cylinder) to the single crankpin, while the remaining cylinders' articulated rods connect to knuckle pins installed around the big-end flange of the master rod.

Explanation: The standard firing order for standard 4-cylinder horizontally opposed Lycoming and Continental aircraft engines is 1 - 3 - 4 - 2. Cylinder 1 is right rear, Cylinder 2 is right front, Cylinder 3 is left rear, and Cylinder 4 is left front (or vice-versa depending on manufacturer layout conventions), ensuring balanced power impulses and minimal vibration.

Explanation: Hydraulic valve lifters use pressurized engine oil inside a plunger mechanism to automatically adjust for thermal expansion and wear, maintaining zero valve clearance (zero lash) throughout engine operating temperatures. This reduces valve train wear, eliminates manual clearance adjustments, and ensures consistent valve timing.

Explanation: Detonation is the rapid, explosive uncontrolled burning of the end-gas (unburned fuel-air mixture) after normal spark ignition has occurred. Pre-ignition occurs when the fuel-air charge is ignited by a localized hot spot (e.g., incandescent carbon deposit or hot valve) prior to the timed spark plug discharge.

Explanation: Compression ratio is defined as the total cylinder volume at BDC divided by the clearance volume at TDC: CR = (Swept Volume + Clearance Volume) / Clearance Volume CR = (90 cu in + 15 cu in) / 15 cu in = 105 / 15 = 7:1.