What does thermal growth mean in engine components, and how does it affect clearances?

• A. Thermal contraction of parts with temperature; design clearances must tighten.
• B. It reduces engine efficiency.
• C. Thermal expansion of parts with temperature; design clearances must accommodate growth to avoid rubbing.
• D. It only affects cosmetic appearance.

Answer: (C)

Thermal growth means that engine parts expand as their temperature rises. When the engine runs, components heat up and grow in size according to their materials’ coefficients of expansion. Because different parts expand at different rates, the gaps between parts change. Designers set clearances so these gaps still stay within acceptable limits when hot, preventing rubbing or interference as components grow. This is why clearances are specified to accommodate growth during operation, ensuring reliable fit and performance.

Cosmetic or efficiency-only effects aren’t what this concept is about, and contraction isn’t the focus here—the emphasis is on expansion with temperature and sizing clearances to handle that growth.