Valve-to-Seat Concentricity Measurement Procedure

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora and 2001 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

Checking the valve-to-seat concentricity determines whether the valve and seat are sealing properly.
You must measure the valve face and the valve seat to ensure proper valve sealing.

Coat the valve face lightly with blue dye (3).
Install the valve in the cylinder head.
Turn the valve against the seat with enough pressure to wear off the dye.
Remove the valve from the cylinder head.
Inspect the valve face.
- If the valve face is concentric, providing a proper seal, with the valve stem, a continuous mark will be made around the entire face (1).
  
  Fig 1: Checking Valve-To-Seat Concentricity
  Courtesy of GENERAL MOTORS CORP.
  
  Important: The wear mark MUST be at least 0.5 mm (0.020 in) from the outer diameter, the margin, of the valve. If the wear mark is too close to the margin the seat must be reconditioned to move the contact area away from the margin.
- If the face is not concentric with the stem, the mark will NOT be continuous around the valve face and the valve should be refaced or replaced and the seat must be reconditioned using the Valve and Seat Reconditioning Procedure.