If the No. 3 cylinder of a nine-cylinder radial engine fails to hold pressure after rotating the crankshaft, how is this usually interpreted?

When the No. 3 cylinder of a nine-cylinder radial engine fails to hold pressure after rotating the crankshaft, this is typically interpreted as a potential issue with the exhaust valve. A damaged exhaust valve or insufficient clearance can prevent the valve from seating properly, leading to a loss of compression in that cylinder. This loss of pressure indicates that engine efficiency may be compromised since the combustion process relies on maintaining adequate pressure in each cylinder for optimum performance.

In radial engines, valve operation is crucial for maintaining proper combustion. If the exhaust valve is damaged, it may not close completely, leading to blow-by, where combustion gases escape during the power stroke. Insufficient exhaust valve clearance may also result in similar problems, as it can prevent the valve from sealing against the seat correctly due to continuous contact with the valve lifters or guides, leading to a loss of compression in the cylinder. Thus, identifying the issue with the exhaust valve is essential for diagnosing and rectifying the pressure problem in that cylinder.