Enter the diameter of the piston, cylinder bore, piston-to-wall clearance, and valve diameter into the calculator to determine the valve clearance.

Piston Valve Clearance Formula

The following formula is used to calculate the piston valve clearance. 

VC = (D + C) - (P + V)

Variables:

  • VC is the valve clearance (mm)
  • D is the diameter of the piston (mm)
  • C is the cylinder bore (mm)
  • P is the piston-to-wall clearance (mm)
  • V is the valve diameter (mm)

To calculate the piston valve clearance, add the diameter of the piston to the cylinder bore. Then, add the piston-to-wall clearance to the valve diameter. Subtract the second result from the first to get the valve clearance.

What is a Piston Valve Clearance?

Piston valve clearance, also known as valve lash, is the gap between the top of the valve stem and the rocker arm or camshaft (depending on the engine design). This clearance is crucial for the proper functioning of the engine as it allows for the expansion of the valve and other components as they heat up during engine operation. If the clearance is too small, the valve may not close properly, leading to loss of power and potential engine damage. If the clearance is too large, the valve may not open fully, also leading to loss of power and excessive wear on the valve train components.

How to Calculate Piston Valve Clearance?

The following steps outline how to calculate the Piston Valve Clearance.

  1. First, determine the diameter of the piston (D) in millimeters.
  2. Next, determine the cylinder bore (C) in millimeters.
  3. Next, determine the piston-to-wall clearance (P) in millimeters.
  4. Next, determine the valve diameter (V) in millimeters.
  5. Finally, calculate the Piston Valve Clearance (VC) using the formula: VC = (D + C) – (P + V).
  6. After inserting the values of D, C, P, and V into the formula, calculate the result.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Diameter of the piston (D) = 50 mm

Cylinder bore (C) = 75 mm

Piston-to-wall clearance (P) = 5 mm

Valve diameter (V) = 30 mm