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Master and articulated rods in an 18-cylinder radial

Aviation Mechanic Powerplant (AMP) practice question 5 of 13 on Reciprocating Engines. ACS element AM.III.A.K5 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONHow many master rods and articulated rods are used in an 18-cylinder, two-row radial engine?

  1. AOne master rod and 17 articulated rods
  2. BTwo master rods and 16 articulated rods
  3. CNine master rods and nine articulated rods
Show the answer and explanation

Correct answer: B. Two master rods and 16 articulated rods

  • A — incorrect A single master rod serves only one row; a two-row engine needs one master rod per row.
  • B — correct One piston in each row is connected by a master rod, so two rows give two master rods and the remaining 16 pistons use articulated rods.
  • C — incorrect Only one cylinder per row uses a master rod, not every other cylinder in the engine.

BACKGROUND

The master-and-articulated rod assembly is commonly used in radial engines. In each row of cylinders, one piston is connected to the crankshaft by a master rod, and all the other pistons in that row are connected to the master rod by articulated rods. An 18-cylinder engine has two rows of cylinders, so it uses two master rods and 16 articulated rods. The articulated rods are forged steel alloy in an I or H cross-section, with bronze bushings pressed into each end to serve as knuckle-pin and piston-pin bearings.

STUDY TIP

Count master rods by rows, not by cylinders: master rods equal the number of rows, and articulated rods are the total cylinders minus the number of rows.

KEY POINTS

  • One master rod serves each row of a radial engine.
  • An 18-cylinder, two-row radial uses two master rods and 16 articulated rods.
  • Articulated rods attach to the master rod flanges with knuckle pins.

SOURCES

  • FAA-H-8083-32B ch01 "Master-and-Articulated Rod Assembly"
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MORE ON RECIPROCATING ENGINES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.