Open-Door Isolation Diagnostic Test: Identifying Lock Binding vs Door Sag
Engineering Overview: Diagnostic guide for identifying whether stiff key rotation is caused by internal pin binding, M5 screw over-torque, or door hinge settlement.
Technical & Engineering Specifications
| Root Causes | Door Hinge Settlement (80%) vs Cylinder Over-Torque (20%) |
|---|---|
| Diagnostic Test | Open-Door Isolation Diagnostic Test |
| Fix for Cylinder | Loosen M5 screw to 4.0 N.m; apply dry PTFE spray |
| Fix for Door Sag | Adjust 3D door hinges or file strike plate lip |
Diagnostic Flowchart for Stiff Locks
When a key is difficult to turn, diagnose the root cause with the Open Door Test:
- Open Door Test: Open the door leaf fully and turn the key.
- If the key turns smoothly with door open: The issue is door sag or strike plate misalignment, not the cylinder.
- If the key is stiff with door open: The cylinder M5 screw is over-tightened, or internal pin chambers are gummed with wrong oil.
- Remedy: Re-align strike plate or hand-loosen M5 screw by 1/4 turn.
Frequently Asked Engineering & Selection Questions
Q1: What is the key installation rule for this cylinder?
Diagnostic guide for identifying whether stiff key rotation is caused by internal pin binding, M5 screw over-torque, or door hinge settlement.