How to Check a Cylinder Head for Flatness

Written by david marsh
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How to Check a Cylinder Head for Flatness
If you don't check the condition of the cylinder head, the gasket will fail. (motorcycle image by Greg Pickens from

The cylinder head sits atop the engine block and holds the valves, spark plugs, valve springs and the intake and exhaust manifolds. It forms the top part of the combustion chamber, and is bolted onto the engine block with a metal, fibre or combination gasket sealing the joining. The gasket isn't as strong as the metal of the engine, however, and has to be supported completely, at every point, to survive the pressure of engine operation. There can't be any gaps along the entire surface of the engine block and the cylinder head. A gap as little as 0.002 inches can be enough for the gasket to lose support and fail. Measuring the flatness of the cylinder head is vital for the engine to do its job.

Skill level:

Things you need

  • Metal ruler
  • Feeler Gauge
  • Brake Cleaner
  • Paper towel
  • Shop manual

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  1. 1

    Put the cylinder head in a vice or stable platform.

  2. 2

    Clean the surface of the cylinder head with the brake cleaner and paper towel.

  3. 3

    Consult the shop manual for the gasket or cylinder head for the minimum gap allowed.

  4. 4

    Take measurement across the length of the cylinder head at the top, middle and bottom and diagonally in both directions.

  5. 5

    Place the blade of the feeler gauge on the cylinder head and lay the ruler on top of the gauge. Withdraw the gauge. If it comes out easily, there's a gap.

Tips and warnings

  • Don't lay the ruler on the cylinder head and try to jam the feeler gauge underneath. This will damage the front edge of the blade.

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