CPL Troubleshooting & Repair of Locks 2 — Questions and Answers
Question 1: A mortise lock cylinder spins freely when the key is turned but does not retract the bolt. What is the most likely cause?
- Broken cam or tailpiece (Correct answer)
- Worn key cuts
- Incorrect keyway
- Frozen plug
Correct answer: Broken cam or tailpiece
A freely spinning cylinder with no bolt movement indicates the cam or tailpiece connecting the cylinder to the bolt mechanism is broken or detached.
Question 2: Which lubricant is generally recommended for pin tumbler lock cylinders to avoid attracting dirt and debris?
- WD-40
- Graphite powder (Correct answer)
- Petroleum-based grease
- Silicone spray mixed with oil
Correct answer: Graphite powder
Graphite powder is the preferred dry lubricant for pin tumbler cylinders because it does not attract dirt or gum up the internal components.
Question 3: A wafer tumbler lock is difficult to turn even after the correct key is inserted. Which condition is the most probable cause?
- Incorrect key bitting
- Worn or deformed wafers binding in the housing (Correct answer)
- Broken driver spring
- Oversized keyway
Correct answer: Worn or deformed wafers binding in the housing
Worn or bent wafers that drag against the housing create binding, making the lock hard to turn even with the correct key.
Question 4: When disassembling a pin tumbler cylinder for repair, a follower tool is used primarily to:
- Remove the retaining clip
- Keep the driver pins and springs from falling out (Correct answer)
- Depress the shear line pins
- Align the plug with the shell
Correct answer: Keep the driver pins and springs from falling out
A follower maintains pressure on the driver pins and springs so they stay seated in the shell when the plug is removed.
Question 5: A deadbolt throws only halfway before stopping. After ruling out hinge and door alignment issues, what internal component should be inspected next?
- The strike plate depth
- A broken or weak bolt spring (Correct answer)
- The keyway profile
- The cylinder cam length
Correct answer: A broken or weak bolt spring
A weak or broken bolt spring can prevent the deadbolt from completing its full throw, causing it to stop partway.
Question 6: During rekeying, a locksmith discovers one pin chamber has a driver pin that is too short. The most likely symptom of this defect is:
- The key will not insert
- The lock opens without a key (false set) (Correct answer)
- The plug rotates too freely under tension
- The lock becomes unpickable
Correct answer: The lock opens without a key (false set)
An undersized driver pin may allow the plug to rotate without all pins reaching the shear line, creating a false set or unintended opening.
Question 7: A customer reports their knob lock's latch does not retract fully when the knob is turned. The most common mechanical cause is:
- A misaligned strike plate
- A broken or seized latch spring (Correct answer)
- A worn key bitting
- An incorrect cam length
Correct answer: A broken or seized latch spring
A broken or seized latch spring prevents the latch bolt from fully retracting when the knob is turned, even if the mechanism is otherwise functional.
CPL Troubleshooting & Repair of Locks 2
A mortise lock cylinder spins freely when the key is turned but does not retract the bolt.
What is the most likely cause?