EM-42 ENGINE MECHANICAL — Cylinder Head 3. CLEAN COMBUSTION CHAMBER Using a wire brush, remove all the carbon from the combustion chambers. NOTICE: Be careful not to scratch the head gasket contact surface. 4. CLEAN VALVE GUIDE BUSHINGS Using a valve guide brush and solvent, clean all the valve guide bushings. 5. CLEAN CYLINDER HEAD Using a soft brush and solvent, thoroughly clean the head. 6. INSPECT CYLINDER HEAD FOR FLATNESS Using a precision straight edge and thickness gauge, measure the surface contacting the cylinder block and manifold for warpage. Maximum warpage: 0.10 mm (0.0039 in.) If warpage is greater than maximum, replace the cylinder head.