Cylinder Head Distortion

WARNING: This page is about a different car, the 2012 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.

Remove any oil, scale, gasket, sealant and carbon deposits from the cylinder head surface.
CAUTION: Do not allow any debris to enter the oil or coolant passages.
Measure the bottom surface of the cylinder head for distortion in six directions as shown, using suitable tools.
Standard: 0.03 mm (0.0012 in)

Limit: 0.1 mm (0.004 in)
- If measurement exceeds the limit, replace the cylinder head.
  
  Fig 1: Checking Cylinder Head Distortion Using Feeler Gauge And Straightedge
  Courtesy of NISSAN NORTH AMERICA, INC.