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In camshaft terminology, the base circle, also known as the cam heel, refers to the lowest point or portion of the camshaft lobe profile.

Base Circle (Camshaft):

  • Definition:
  • The base circle is the cylindrical or nearly cylindrical portion of the camshaft lobe that does not contribute to the lifting of the valve. It is the portion of the camshaft profile where the cam follower (such as a lifter or tappet) rests when the valve is closed.
  • Characteristics:
  • Lowest Point: It represents the minimum diameter of the cam lobe profile.
  • No Lift: During engine operation, when the camshaft rotates and the cam lobe is not engaging the valve lifter, the valve remains closed as the cam follower rides on the base circle.
  • Shape: Typically smooth and designed to ensure minimal wear and smooth operation where contact with the valve lifter occurs.
  • Function:
  • Valve Control: The cam lobe’s profile transitions from the base circle to the cam lobe’s highest point (nose or peak) where maximum lift of the valve is achieved.
  • Timing: The base circle defines the initial position of the cam lobe relative to the valve, influencing the timing of valve opening and closing.
  • Cam Heel:
  • Synonym: Often referred to as the “cam heel,” especially in automotive engineering contexts.


  • Precision: The size and shape of the base circle are critical for precise valve timing and engine performance.
  • Wear Resistance: Engine designers and manufacturers pay close attention to the base circle’s material and surface treatment to ensure durability and minimal wear on the camshaft and valve train components.
  • Performance: Properly designed base circles contribute to smooth engine operation, reduced noise, and optimized power delivery.

The base circle (or cam heel) on a camshaft is a fundamental element in the timing and operation of an engine’s valve train. It serves as the resting position for valve lifters and plays a crucial role in determining valve timing and engine performance characteristics. Understanding its function and dimensions is essential for camshaft design and maintenance in automotive and other mechanical applications.

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