ACS Powerplant Systems & Engine Overhaul 2 — Questions and Answers
Question 1: During engine overhaul, what is the primary purpose of magnaflux inspection?
- Detect surface and subsurface cracks in ferrous metal parts (Correct answer)
- Measure dimensional tolerances of rotating components
- Check for corrosion on aluminum cylinder heads
- Verify oil passage alignment in the crankcase
Correct answer: Detect surface and subsurface cracks in ferrous metal parts
Magnaflux (magnetic particle inspection) detects surface and subsurface cracks in ferrous metal parts by revealing disruptions in magnetic flux lines.
Question 2: What does the term 'dry tappet clearance' refer to in reciprocating engine maintenance?
- Valve clearance measured with the engine cold and hydraulic lifters collapsed (Correct answer)
- Oil clearance between the camshaft lobe and the follower
- Clearance between piston rings and cylinder wall
- Gap between the crankshaft and main bearing with no oil pressure
Correct answer: Valve clearance measured with the engine cold and hydraulic lifters collapsed
Dry tappet clearance is the valve clearance measured with the engine cold and hydraulic lifters fully collapsed, used to verify proper valve train geometry.
Question 3: Which type of engine oil system is most commonly used in modern horizontally opposed aircraft engines?
- Wet sump (Correct answer)
- Dry sump with remote reservoir
- Pressure spray with no sump
- Total loss system
Correct answer: Wet sump
Most horizontally opposed aircraft engines use a wet sump system where oil is stored in a sump at the bottom of the crankcase.
Question 4: What is the purpose of a compensating port in an aircraft engine fuel injection system?
- To meter air reference pressure so fuel flow remains consistent with changes in throttle position (Correct answer)
- To drain excess fuel back to the fuel tank
- To supply additional enrichment fuel during takeoff
- To equalize pressure between cylinders in the induction manifold
Correct answer: To meter air reference pressure so fuel flow remains consistent with changes in throttle position
The compensating port references throttle body air pressure so the fuel injector's differential pressure accurately reflects engine airflow regardless of throttle position.
Question 5: During a top overhaul, a technician finds chrome cylinder walls. What special consideration applies?
- Chrome cylinders must use cast iron piston rings, not chrome rings (Correct answer)
- Chrome cylinders require higher-viscosity oil for break-in
- Chrome cylinders cannot be re-honed and must be replaced
- Chrome cylinders require a longer break-in period than steel cylinders
Correct answer: Chrome cylinders must use cast iron piston rings, not chrome rings
Chrome-plated cylinders must be fitted with cast iron piston rings because two chrome surfaces together will not seat properly and will cause excessive wear.
Question 6: What is 'nitriding' as applied to aircraft engine crankshafts?
- A surface hardening process using nitrogen gas to increase wear resistance (Correct answer)
- A chemical cleaning process to remove carbon deposits from journal surfaces
- A cadmium plating process applied to crankshaft journals
- A heat treatment to relieve internal stress after grinding
Correct answer: A surface hardening process using nitrogen gas to increase wear resistance
Nitriding is a surface hardening process in which the crankshaft is exposed to ammonia gas at elevated temperature, infusing nitrogen into the steel to create a hard wear-resistant surface layer.
Question 7: An aircraft engine shows a high oil consumption but normal oil pressure. Which condition is MOST likely?
- Worn or broken piston rings allowing oil to enter the combustion chamber (Correct answer)
- Clogged oil filter bypassing dirty oil to the bearings
- Failed oil pressure relief valve stuck open
- Cracked engine case leaking oil externally
Correct answer: Worn or broken piston rings allowing oil to enter the combustion chamber
Worn or broken piston rings are the most common cause of high oil consumption with normal pressure, as oil bypasses the rings and burns in the combustion chamber.
ACS Powerplant Systems & Engine Overhaul 2
During engine overhaul, what is the primary purpose of magnaflux inspection?