The part of a camshaft that converts rotary motion to reciprocating motion is called

• A. the pushrod
• B. the lifter
• C. the lobe
• D. the journal

Answer: (C)

The lobe is the part that does the work. Its raised profile on the camshaft pushes against the lifter as the camshaft rotates. This contact converts the shaft’s continuous rotary motion into the lifter’s up-and-down (reciprocating) motion, which is then transmitted through the pushrod to the rocker arm and valve. The journal is simply the bearing surface that supports the camshaft as it turns, not the part that creates the reciprocating motion. The lifter plays a role in following the lobe, but the actual conversion from rotary to reciprocating motion is accomplished by the cam lobe.