What is the purpose of counterweights on a crankshaft?

• A. Balance the off-center weight of the individual crank throws
• B. Increase the engine's compression ratio
• C. Improve piston cooling
• D. Decrease oil consumption

Answer: (A)

Balancing rotating masses in the cranktrain to reduce vibration and bearing loads. Counterweights on the crankshaft are added to offset the off-center weight of the crank throws. As the crank turns, each throw and its connected components create fluctuating inertial forces that would shake the engine. The counterweights provide an opposite effect, canceling out those forces and smoothing the engine’s operation, which also helps protect bearings and allows smoother performance at higher RPM.

The other options don’t fit because compression ratio is set by piston and chamber geometry, not by counterweights; piston cooling is a function of cooling systems and piston design; and oil consumption is influenced by seals, rings, and lubrication management, not by balancing weights on the crank.