🔍 Key Concepts

• Difference between "barred over" manually and "cranked over" on starting air or electric starter • What a seized piston or bad bearing would feel like when you try to turn the engine by hand • How an air start system works and what happens if air cannot get to the starting motor or starting valves

💭 Think About

• If the engine can be turned by hand with a bar, what does that tell you about the internal mechanical condition of pistons and bearings? • Which of the listed problems would completely prevent the starter from being able to rotate the engine, even though it is free to turn mechanically? • Which option is most directly related to the starting system rather than the internal engine condition?

✅ Before You Answer

• Confirm that "seized" or badly fitted internal parts usually make the engine hard or impossible to bar over • Think about whether insufficient compression would stop the crankshaft from rotating, or just make it fail to fire • Consider how a closed/blocked starting air line or valve would affect the starter’s ability to turn the engine, even if the engine itself turns freely by hand