FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
A technician is torquing the cylinder base (hold-down) nuts on a horizontally opposed engine cylinder that has just been reinstalled. What is the correct general procedure for applying final torque to these nuts?
- ATorque only the two nuts nearest the exhaust port first, then leave the remaining nuts finger-tight
- BTorque each nut fully to final value in a single pass, working around the cylinder in a clockwise direction
- CTorque the top nuts to full value, then the bottom nuts to full value, working top to bottom
- DApply torque in incremental steps using a crisscross (star) pattern until final torque value is reached on all nuts
Show answer & explanationAnswer & explanation
Correct answer: D. Apply torque in incremental steps using a crisscross (star) pattern until final torque value is reached on all nuts
Cylinder base nuts, like other multi-fastener flange joints, must be tightened gradually in a crisscross (star) pattern and in incremental steps to final torque. This method distributes clamping load evenly, prevents cylinder base flange warping or distortion, and ensures a proper seal.
Why the other options are wrong
- A. Leaving nuts finger-tight risks an uneven, leaking, or loose joint and is not proper procedure.
- B. A single-pass sequential torque around the circle can cause uneven clamping and flange distortion.
- C. Torquing one side fully before the other creates an uneven, cocked seating of the cylinder base.
Cylinder Base Nut Torque Sequence
The crisscross, incremental tightening pattern used on cylinder hold-down nuts (and similar circular fastener patterns) to achieve even clamping and prevent distortion.
- Crisscross/star pattern spreads load evenly
- Torque applied in 2-3 incremental steps to final value
- Prevents cylinder base flange warping and gasket leaks
Memory trick: Star pattern spreads the squeeze evenly — no favorites!