FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesHard
A technician is diagnosing a lifter noise complaint on an engine equipped with hydraulic valve lifters. During engine operation, the hydraulic lifter is designed to automatically compensate for valve train clearance. What component within the hydraulic lifter allows this automatic clearance adjustment?
- AA mechanical screw adjuster set at each inspection
- BA bimetallic spring that expands with heat to close the gap
- CA pneumatic bellows pressurized by intake manifold vacuum
- DA plunger and check valve arrangement using engine oil pressure to take up clearance
Show answer & explanationAnswer & explanation
Correct answer: D. A plunger and check valve arrangement using engine oil pressure to take up clearance
A hydraulic lifter uses a spring-loaded plunger inside a cylinder body with a one-way check valve; engine oil under pressure fills the chamber beneath the plunger, which extends to take up all valve train clearance (zero lash) and maintains it automatically as parts wear or thermally expand.
Why the other options are wrong
- A. Solid lifters, not hydraulic ones, require manual screw adjustment of valve clearance.
- B. Hydraulic lifters do not use bimetallic springs; thermal expansion is compensated hydraulically, not mechanically via bimetal.
- C. Hydraulic lifters use engine oil pressure, not intake manifold vacuum or pneumatic bellows.
Hydraulic Valve Lifter
A valve lifter that uses a spring-loaded plunger and one-way check valve, filled with pressurized engine oil, to automatically maintain zero valve clearance during engine operation.
- Uses engine oil pressure to extend the internal plunger
- Check valve traps oil to maintain zero-lash clearance
- Automatically compensates for thermal expansion and wear
Memory trick: Oil fills the plunger like a hydraulic jack, quietly taking up all the slack automatically.