FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
A mechanic is adjusting valve clearance on a reciprocating engine equipped with solid (mechanical) lifters. If the clearance is set too tight (less than specified), what is the most likely result?
- AOil consumption will increase without affecting valve operation
- BExcessive mechanical noise will occur with no risk of engine damage
- CThe valve will fail to open at all, causing complete loss of cylinder power only
- DThe valve will not fully seat and close, leading to a burned or warped valve from combustion gas leakage
Show answer & explanationAnswer & explanation
Correct answer: D. The valve will not fully seat and close, leading to a burned or warped valve from combustion gas leakage
Insufficient valve clearance means the valve train has no room to accommodate thermal expansion, so the valve is held slightly off its seat during the compression/power stroke. This allows hot combustion gases to leak past the valve face, rapidly burning and warping the valve.
Why the other options are wrong
- A. Valve clearance issues directly affect valve seating and sealing, not primarily oil consumption.
- B. Tight clearance is actually quieter, not noisier, and does risk serious engine damage.
- C. Excessive (not insufficient) clearance would cause delayed opening and reduced lift/power.
Valve Clearance (Solid Lifters)
The small gap in the valve train that allows for thermal expansion; too little clearance prevents full valve seating and causes burning, while too much clearance causes noise and reduced lift.
- Too tight = valve doesn't fully close, burns valve
- Too loose = noisy, reduced valve lift/timing accuracy
- Checked and adjusted with feeler gauge per manufacturer spec
Memory trick: Too tight, valve can't shut tight—hot gas burns it out.