FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesHard
During overhaul of a large single-row radial engine, a technician examines the component that has cam tracks machined on its outer circumference to actuate the valve mechanism through cam rollers and pushrods. What is this component called?
- AImpeller shaft
- BCam ring
- CAccessory drive gear
- DMaster rod
Show answer & explanationAnswer & explanation
Correct answer: B. Cam ring
The cam ring is a circular plate with machined cam tracks (lobes) on radial engines that rotates at a reduced speed relative to the crankshaft to open and close the intake and exhaust valves via cam rollers, pushrods, and rocker arms. The number of lobes and cam ring speed determine valve timing for all cylinders in the row.
Why the other options are wrong
- A. The impeller shaft drives the supercharger impeller, not the valves.
- C. The accessory drive gear powers magnetos, pumps, and generators, not valve actuation.
- D. The master rod connects directly to the crankshaft and carries the articulating rods, unrelated to valve actuation.
Cam Ring (Radial Engine)
A geared ring with cam tracks on its circumference that rotates at reduced speed to actuate valve mechanisms on a radial engine via cam rollers and pushrods.
- Rotates at a fraction of crankshaft speed
- Number of lobes depends on cylinders per row
- Actuates pushrods/rocker arms for intake and exhaust valves
Memory trick: The cam RING rings the valves open in RHYTHM around the row.