FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
On a large radial reciprocating engine, one connecting rod is attached directly to the crankpin of the crankshaft, and the remaining connecting rods for that row of cylinders attach to knuckle pins on that rod. What is this central connecting rod called?
- ALink rod
- BArticulating rod
- CMaster rod
- DWrist pin rod
Show answer & explanationAnswer & explanation
Correct answer: C. Master rod
The master rod is the single connecting rod in each row of a radial engine that attaches directly to the crankpin; all other connecting rods (link/articulating rods) in that row attach to knuckle pins around the perimeter of the master rod's big end.
Why the other options are wrong
- A. Link rods (also called articulating rods) attach to the master rod, not the crankshaft directly.
- B. Articulating rod is another name for the link rods that attach to the master rod, not the central rod itself.
- D. A wrist pin connects the piston to the connecting rod's small end; there is no 'wrist pin rod' term.
Master Rod / Link Rod (Radial Engine)
In a radial engine, the master rod connects directly to the crankshaft crankpin; the remaining link (articulating) rods attach to knuckle pins on the master rod's big end.
- One master rod per row of cylinders
- Link rods pivot on knuckle pins around master rod
- Design allows multiple cylinders to share one crankpin
Memory trick: Master rod is the hub of a wheel—other rods (spokes) attach to it, not the axle directly.