22 Reciprocating Engines Practice Questions & Answers

1. 1. In what order do the five events of the four-stroke cycle occur in a reciprocating aircraft engine?

   • A.Intake, compression, ignition, power, exhaust✓ Answer
   • B.Compression, intake, ignition, power, exhaust
   • C.Intake, compression, power, ignition, exhaust
   • D.Intake, ignition, compression, power, exhaust

   The four-stroke cycle contains five events spread over only four piston strokes. The spark occurs near the end of the compression stroke, so ignition falls between compression and power; the burning charge then drives the piston down and the exhaust event clears the cylinder.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, five events of the four-stroke cycleReport a problem with this question

2. 2. One complete four-stroke cycle in a single cylinder requires how much rotation?

   • A.One crankshaft revolution, while the camshaft turns twice
   • B.Two crankshaft revolutions, while the camshaft turns once✓ Answer
   • C.Two crankshaft revolutions, while the camshaft turns three times
   • D.Four crankshaft revolutions, while the camshaft turns twice

   Four piston strokes take 720 degrees, or two turns of the crankshaft. Each valve must open only once in that cycle, so the camshaft or cam ring is geared to turn at one-half crankshaft speed and completes one revolution per cycle.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, crankshaft and camshaft speed relationshipReport a problem with this question

3. 3. At what point in the cycle does valve overlap occur?

   • A.End of the compression stroke and start of the power stroke
   • B.End of the power stroke and start of the exhaust stroke
   • C.End of the exhaust stroke and start of the intake stroke✓ Answer
   • D.End of the intake stroke and start of the compression stroke

   Overlap is the crankshaft travel during which both valves are off their seats near top center, between the exhaust and intake events. The intake valve opens before top center while the exhaust valve is still closing, so the departing gases help start the fresh charge moving into the cylinder.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, valve timing and valve overlapReport a problem with this question

4. 4. Which of the following is a purpose of valve overlap?

   • A.Greater combustion pressure toward the end of the power event
   • B.Slower exhaust gas velocity through the port and exhaust stack
   • C.Improved volumetric efficiency and added cooling of the cylinder✓ Answer
   • D.Reduced cylinder pressure at the start of the compression event

   With both valves open around top center, the inertia of the departing exhaust helps scavenge the cylinder and draw in more charge, so more mixture is inducted for a given displacement. The cool incoming charge also sweeps the combustion chamber and valve area, carrying heat away.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, purposes of valve overlapReport a problem with this question

5. 5. Excessive valve clearance in a reciprocating engine causes the valves to:

   • A.Open early and close late, increasing valve overlap
   • B.Open late and close late, leaving overlap unchanged
   • C.Open late and close early, decreasing valve overlap✓ Answer
   • D.Open early and close early, shortening the power event

   Clearance in the valve train must be taken up by the cam lobe before the valve starts to move, so extra clearance delays opening and hastens closing. Both the duration the valve stays open and the period when both valves are open are therefore reduced.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, valve clearance and its effect on valve timingReport a problem with this question

6. 6. What is the firing order of a nine-cylinder single-row radial engine?

   • A.1-2-3-4-5-6-7-8-9
   • B.1-5-9-4-8-3-7-2-6
   • C.1-4-7-2-5-8-3-6-9
   • D.1-3-5-7-9-2-4-6-8✓ Answer

   A single-row radial always has an odd number of cylinders so the crankshaft can fire every other cylinder around the row. All odd-numbered cylinders fire in numerical succession, then all even-numbered ones, which spaces the power impulses evenly at 80 degrees of crankshaft rotation for smooth, balanced running.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, firing order of radial enginesReport a problem with this question

7. 7. The brake horsepower produced by a reciprocating engine is equal to:

   • A.Friction horsepower minus the indicated horsepower
   • B.Indicated horsepower minus friction horsepower✓ Answer
   • C.Indicated horsepower times thermal efficiency
   • D.Indicated horsepower plus friction horsepower

   Indicated horsepower is the power combustion develops inside the cylinders. Part of it is used turning the engine against its own friction and driving the accessories, and what remains at the propeller shaft is brake horsepower, so bhp equals ihp minus friction horsepower. Mechanical efficiency is bhp divided by ihp.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, indicated, friction, and brake horsepowerReport a problem with this question

8. 8. A cylinder holds 96 cubic inches with the piston at bottom center and 12 cubic inches with the piston at top center. What is its compression ratio?

   • A.1 to 8
   • B.12 to 1
   • C.8 to 1✓ Answer
   • D.7 to 1

   Compression ratio is the total cylinder volume with the piston at bottom center divided by the clearance volume with the piston at top center: 96 divided by 12 equals 8, expressed as 8 to 1. Dividing the two volumes the other way around is the common error.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, compression ratioReport a problem with this question

9. 9. The maximum compression ratio usable in a spark-ignition aircraft engine is limited chiefly by:

   • A.The number of compression rings fitted to each piston head
   • B.The reach and heat range of the spark plugs in the cylinder
   • C.The detonation characteristics of the fuel the engine may burn✓ Answer
   • D.The gear ratio between the camshaft and the engine crankshaft

   Raising the compression ratio raises the temperature and pressure of the charge at the end of compression. Beyond what the approved fuel can tolerate the charge detonates instead of burning smoothly, so fuel grade, together with the structural limits of the engine and the degree of supercharging, sets the ceiling. Spark plug reach is not a limiting factor.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, compression ratio limits and detonationReport a problem with this question

10. 10. Preignition in a reciprocating engine is best described as:

    • A.Ignition of the charge by a spark that is timed too early
    • B.Ignition of the charge inside the intake manifold ahead of the valve
    • C.Violent burning of the charge after the spark plug fires
    • D.Ignition of the charge before the spark, by a local hot spot✓ Answer

    Preignition means the mixture is lit before the ignition system fires it, typically by a glowing carbon particle, a cracked plug insulator, or an overheated valve edge acting as a hot spot. Detonation is different: the plug fires on time and the remaining unburned charge then explodes instead of burning progressively.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, preignition compared with detonationReport a problem with this question

11. 11. During a high-power ground run, cylinder head temperature climbs sharply and the engine loses power and runs rough. If detonation is occurring, the mechanic should:

    • A.Retard the ignition timing and close the cowl flaps to steady combustion
    • B.Reduce power, enrich the mixture, and open the cowl flaps to cool the cylinders✓ Answer
    • C.Increase manifold pressure and lean the mixture to burn the charge faster
    • D.Hold full power until the cylinder head temperature settles back down

    Detonation is driven by charge temperature and pressure, so the corrective action is to take heat and pressure out of the cylinder: reduce power, richen the mixture so the extra fuel cools the charge, and increase cooling airflow. Allowed to continue, detonation erodes piston heads, breaks rings, and burns valves, and the fuel grade actually serviced must also be verified.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, causes, effects, and correction of detonationReport a problem with this question

12. 12. A cam-ground piston is machined with its greatest diameter:

    • A.Perpendicular to the axis of the piston pin✓ Answer
    • B.Parallel to the axis of the piston pin bosses
    • C.At the ring lands, tapering toward the piston head
    • D.At the top land, tapering toward the piston skirt

    The extra metal at the piston-pin bosses expands more than the rest of the skirt as the piston heats, so a piston ground slightly oval, larger across the axis perpendicular to the pin, becomes round at operating temperature. The closer cold fit keeps the piston from slapping or cocking in the bore during warm-up.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, cam-ground pistonsReport a problem with this question

13. 13. Which rings may be installed in a chrome-plated cylinder barrel?

    • A.Chrome-plated rings, which match the hardness of the wall
    • B.Chrome-plated rings used with a cast iron oil control ring
    • C.Cast iron rings, which will seat against the plated wall✓ Answer
    • D.Cast iron rings that are chrome plated on the face only

    Chrome will not wear in against chrome, so chrome-plated rings running in a chrome-plated barrel never seat and the cylinder keeps passing oil and losing compression. Plain gray cast iron rings are used in a plated barrel, while chrome-plated rings belong only in an unplated steel barrel.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, piston rings and chrome-plated cylinder barrelsReport a problem with this question

14. 14. What is the purpose of the metallic sodium sealed inside some exhaust valves?

    • A.It shifts inside the valve and carries heat from the head to the stem✓ Answer
    • B.It adds mass to the valve head so the valve seats more positively
    • C.It strengthens the valve head against the pressure of combustion
    • D.It lubricates the valve stem where it rides in the valve guide

    The sodium melts at operating temperature and sloshes as the valve moves, carrying heat from the hot valve head up the hollow stem to the guide and cylinder head, which lowers the valve's operating temperature. A sodium-filled valve must never be cut open and is disposed of by approved means, because sodium reacts violently with water.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, sodium-filled exhaust valvesReport a problem with this question

15. 15. Nitriding is used on a cylinder barrel in order to:

    • A.Harden the surface of the bore by exposure to ammonia gas✓ Answer
    • B.Create the crosshatch finish that lets new rings seat
    • C.Make the bore slightly smaller at the cylinder head end
    • D.Bring a worn bore back out to its original standard diameter

    Nitriding exposes the machined steel barrel to ammonia at high temperature, and nitrogen combines with the alloying elements to form a hard, wear- and corrosion-resistant case only a few thousandths of an inch deep. Honing produces the crosshatch, chrome plating restores worn dimensions, and choke boring makes the head end smaller so the bore runs straight when hot.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, cylinder barrel construction and nitridingReport a problem with this question

16. 16. Pendulum-type dynamic dampers fitted to the crankshaft cheeks serve to:

    • A.Reduce the torsional vibration set up by the firing impulses✓ Answer
    • B.Damp the surge of the valve springs at high engine speed
    • C.Absorb the thrust load the propeller applies to the crankshaft
    • D.Balance the static weight of the crankshaft and its rods

    Each cylinder's power impulse gives the crankshaft a twisting kick, and the pendulum-type counterweights swing on their pins at the frequency of those impulses and out of phase with them, so the torsional deflection is detuned and absorbed rather than allowed to build. They reduce vibration; they do not eliminate it.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, dynamic dampers and crankshaft balanceReport a problem with this question

17. 17. In a single-row radial engine, why is the stroke of the pistons on the articulated rods not identical to that of the master rod piston?

    • A.The knuckle pins sit off the crankpin center, so link rods swing in an ellipse✓ Answer
    • B.The cylinders are mounted at slightly different distances from the crankcase
    • C.The master rod bearing floats, letting the crankpin shift in its journal
    • D.The articulated rods are made in graduated lengths to suit each bore

    Only the master rod turns about the crankpin center. The articulated rods ride on knuckle pins set in the master rod flange, and because those pins lie on a circle around the crankpin center rather than at it, their big ends travel an elliptical path. Piston travel therefore varies slightly from cylinder to cylinder, and the knuckle pin holes are positioned to compensate in the ignition timing.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, master rod and articulated rod assembliesReport a problem with this question

18. 18. Why is the propeller of a radial engine pulled through by hand before starting?

    • A.To confirm that both magnetos are properly grounded
    • B.To find oil that has drained into the lower cylinders✓ Answer
    • C.To prime the lower cylinders for an easier start
    • D.To circulate engine oil to the main bearings before cranking

    While the engine sits, oil or fuel can drain past the rings and valves into the cylinders that lie below the crankshaft. Liquid does not compress, so cranking against it can bend a rod or crack a cylinder; the propeller is turned by hand with the ignition treated as hot, and any lock found is cleared by removing the lower spark plugs or intake pipes rather than forcing the engine.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, hydraulic lock in radial enginesReport a problem with this question

19. 19. Which condition reduces the volumetric efficiency of a reciprocating engine?

    • A.A reduction in the overall length of the induction ducting
    • B.A high carburetor air temperature entering the induction system✓ Answer
    • C.A cold, dense mass of air arriving at the induction inlet
    • D.An increase in the compression ratio of each engine cylinder

    Volumetric efficiency compares the mass of charge actually taken into the cylinder with what the piston displacement could hold at ambient conditions. Hot induction air is less dense, so less mass enters for the same volume swept. Restricted or sharply bent ducting, high cylinder head temperature, improper valve timing, and a partly closed throttle lower it as well.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, volumetric efficiencyReport a problem with this question

20. 20. During an ignition switch check the rpm does not drop at all when the switch is moved from BOTH to L. The most likely cause is:

    • A.The right magneto is producing a hotter spark than the left
    • B.The left magneto has a lead loose at its distributor block
    • C.The left magneto is timed early to the crankshaft position
    • D.The right magneto is not being grounded through its switch lead✓ Answer

    In the L position the switch is supposed to ground the right magneto so the engine runs on the left one alone, and the loss of one spark per cylinder normally shows as a small rpm drop. No drop at all means the right magneto never stopped firing, which points to an open or disconnected primary lead. That magneto is then hot in every switch position, so the propeller must be treated as live.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), ground operation, ignition switch check and magneto groundingReport a problem with this question

21. 21. In a compression-ignition aircraft engine, the fuel charge is ignited by:

    • A.Timing a high-tension spark to occur before top center
    • B.Compressing a mixture of fuel and air until it ignites itself
    • C.Injecting fuel into air heated by a high compression ratio✓ Answer
    • D.Using a glow plug kept energized through the power stroke

    A compression-ignition engine draws in and compresses air alone, at a ratio high enough that the air temperature exceeds the ignition point of the fuel, and fuel is then injected near the end of compression. There is no ignition system to time, and power is set by the quantity of fuel injected rather than by throttling the air charge.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), Chapter 1, compression-ignition engine operating principlesReport a problem with this question

22. 22. The cobalt chloride crystals in the dehydrator plugs of a stored engine:

    • A.Absorb any fuel vapor left in the cylinder after preserving
    • B.Seal the spark plug hole against outside air in storage
    • C.Turn from pink to blue as preservative oil coats the walls
    • D.Turn from blue to pink as they absorb moisture inside✓ Answer

    Cobalt chloride is blue when dry and turns pink or lavender as it takes up water, so the plugs give a visual check of the moisture inside the cylinders. A plug that has changed color shows the preservation has been compromised and the engine must be re-preserved, and how deeply an engine is preserved depends on whether it is in flyable, temporary, or indefinite storage.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant (FAA-H-8083-32), engine preservation and storage, dehydrator plugsReport a problem with this question

Practice questions based on the Aviation Mechanic Airman Certification Standards (FAA-S-ACS-1), 14 CFR parts 43, 65, and 91, and the FAA Aviation Maintenance Technician Handbook—Powerplant (FAA-H-8083-32). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the POWERPLANT written test only; the General and Airframe written tests and the oral and practical tests are separate. Torque values, running clearances, compression limits, magneto timing angles, spark plug gaps, temperature and pressure limits, servicing quantities, and overhaul intervals always come from the manufacturer's current maintenance data, the type certificate data sheet, and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →