FAA Powerplant Written Practice Test

What is the primary factor in ensuring a gas tight joint between a cylinder barrel and the cylinder head?

1. A tight weld

2. An initial precision fit

3. Use of high-temperature sealant

4. Employing heavy-duty bolts

The correct answer is: An initial precision fit

The primary factor in ensuring a gas-tight joint between a cylinder barrel and the cylinder head is an initial precision fit. A cylinder barrel and a cylinder head must have surfaces that are meticulously machined to ensure they align perfectly without gaps. This precision is crucial because any irregularities or misalignments can lead to leaks, which may compromise the engine's performance and efficiency. When the surfaces are properly fitted, they can create a reliable seal once the components are assembled and subjected to the operating conditions of the engine. This tight fit helps to withstand the pressures and temperatures within the engine, ensuring that gases do not escape from the combustion chamber, which is essential for maintaining optimal engine function and preventing contamination of the lubrication system. While a tight weld, the use of sealants, and heavy-duty bolts can enhance the joint's strength and reliability, they cannot replace the need for an initial precision fit. Each of these aspects plays a supportive role, but the fundamental requirement for a gas-tight joint begins with that accurately machined interface.