FAA Powerplant Written Practice Test

Why is it improper to attempt to straighten a bent crankshaft?

1. It is too costly.

2. It can damage the hardened surfaces.

3. It affects engine balance.

4. It voids manufacturer warranty.

The correct answer is: It can damage the hardened surfaces.

Attempting to straighten a bent crankshaft is improper primarily because it can damage the hardened surfaces of the crankshaft. Crankshafts are typically made from high-strength steel or cast iron and are subjected to rigorous heat treat processes that harden their surface. These hardened surfaces are crucial for maintaining the crankshaft's structural integrity and wear resistance. When a crankshaft is bent, the stresses and strains involved in the straightening process can lead to micro-cracking or surface deformation, seriously compromising the durability and performance of the crankshaft. Such damage can result in increased friction, potential failure, and catastrophic engine damage when the crankshaft is put back into operation. While considerations like cost, engine balance, and manufacturer warranty play important roles in engine maintenance and repair decisions, the fundamental concern lies in the mechanical properties of the crankshaft itself and the risk of damaging those properties if the crankshaft is straightened improperly. Therefore, the best practice is to replace a bent crankshaft rather than attempt to repair it through straightening.