What cautions should be taken when performing a compression check on a reciprocating engine?

What cautions should be taken when performing a compression check on a reciprocating engine?

• A. Connecting air pressure to the cylinder can cause the propeller to rotate suddenly; contain the propeller; two-person approach.
• B. Only wear safety glasses.
• C. Disconnect the battery and ignition.
• D. No special precautions are required.

Answer: (A)

When you pressurize a cylinder to check compression, the air can push the piston and turn the crank, which may cause the propeller to rotate suddenly. That’s why the right precaution is to contain the propeller and use a two-person approach: one person keeps the prop secured so it can’t move, while the other monitors the test and reads the gauge. This setup prevents a dangerous prop strike and ensures the reading is taken safely. Wearing safety glasses alone isn’t enough, and saying no special precautions are needed isn’t correct. Disconnecting ignition is good practice too, but the safety focus described here is on preventing sudden prop rotation due to the introduced air.

When you pressurize a cylinder to check compression, the air can push the piston and turn the crank, which may cause the propeller to rotate suddenly. That’s why the right precaution is to contain the propeller and use a two-person approach: one person keeps the prop secured so it can’t move, while the other monitors the test and reads the gauge. This setup prevents a dangerous prop strike and ensures the reading is taken safely. Wearing safety glasses alone isn’t enough, and saying no special precautions are needed isn’t correct. Disconnecting ignition is good practice too, but the safety focus described here is on preventing sudden prop rotation due to the introduced air.