FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
A technician is inspecting a cylinder barrel from a high-hour reciprocating engine. Measurements indicate that the cylinder diameter is largest near the top of the cylinder (combustion end) and gradually tapers towards the crankshaft end. This condition is known as:
- ACylinder out-of-roundness.
- BCylinder scoring.
- CCylinder choke.
- DCylinder taper.
Show answer & explanationAnswer & explanation
Correct answer: D. Cylinder taper.
Cylinder taper refers to the condition where the cylinder bore is worn to a larger diameter at the top (combustion end) than at the bottom (crankshaft end). This wear pattern is common in reciprocating engines due to higher temperatures, pressures, and piston ring forces at the top of the cylinder during combustion.
Why the other options are wrong
- A. Cylinder out-of-roundness describes an elliptical shape of the cylinder bore, not a gradual change in diameter along its length.
- B. Cylinder scoring refers to scratches or grooves in the cylinder wall, which is a different type of wear than a gradual change in diameter.
- C. Cylinder choke is a design feature where the cylinder bore is intentionally manufactured with a slightly smaller diameter at the top when cold, to compensate for thermal expansion during operation, keeping it cylindrical at operating temperature. This is a design, not a wear condition.
Cylinder Taper (Wear)
A common wear pattern in reciprocating engine cylinders where the bore diameter is larger at the combustion end than at the crankshaft end.
- Larger diameter at top (combustion end).
- Gradually tapers smaller towards bottom.
- Caused by heat, pressure, ring forces.
Memory trick: Taper is like a 'T' for Top-heavy wear, getting wider at the top.