SkyDrill

Manufacturer approval before staking a valve

Aviation Mechanic Powerplant (AMP) practice question 8 of 13 on Reciprocating Engines. ACS element AM.III.A.R3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA cylinder still reads low on a compression check after the valve clearance is found to be correct. Before staking the valve with a fiber drift, what must the technician confirm?

  1. AThat the ignition switch is in the BOTH position
  2. BThat the engine has cooled to ambient temperature
  3. CThat the manufacturer approves the procedure
Show the answer and explanation

Correct answer: C. That the manufacturer approves the procedure

  • A — incorrect The ignition switch must be OFF during a compression test so there is no accidental firing of the engine.
  • B — incorrect Compression tests are made as soon as possible after shutdown while parts are still freshly lubricated, not after the engine has cooled.
  • C — correct The handbook states that staking the valve should only be performed if approved by the manufacturer.

BACKGROUND

When low compression is found, the engine is run to takeoff power and the cylinder is rechecked; if the reading is still low, the rocker-box cover is removed and valve clearance is checked. If inadequate valve clearance is not the cause, a fiber drift may be placed on the rocker arm over the valve stem and tapped with a one to two pound hammer to dislodge foreign material lodged between the valve and seat. The crankshaft must then be rotated to reseat the valve before compression is rechecked, because the higher seating velocity from staking can mask slightly egged or eccentric valve seats. The handbook is explicit that this procedure should only be performed if approved by the manufacturer.

STUDY TIP

Treat any technique the handbook flags with a manufacturer-approval condition as off limits until you have found that approval in the engine data.

KEY POINTS

  • Staking a valve with a fiber drift is allowed only when the manufacturer approves it.
  • Rotate the crankshaft to reseat the valve before rechecking compression.
  • The ignition switch stays OFF throughout the compression test.

SOURCES

  • FAA-H-8083-32B ch10 "Differential Pressure Tester"
  • FAA-H-8083-32B ch10 "Cylinder Compression Tests"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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.