VALVE GP-RELIEF 4888375 - Caterpillar

Remove all carbon deposits from the angled surface at the bottom of the cylinder head bore for the unit injector. Failure to clean this area may prevent the unit injector from seating properly. This could result in failure of the unit injector due to leakage of exhaust gas into the fuel passage.
It is very important for the cylinder head bore for the unit injector to be clean when the unit injector is replaced. Use the following procedure to clean the cylinder head bore for the unit injector.
Partial cross section of a cylinder head(1) Bore for the unit injector(2) Seat for the unit injector A fine grade of "Scotch Brite" material is the preferred material for cleaning. The product is listed in the "Tools and Shop Products Guide" in a roll as the 1U-5512 Cut/Polish Roll and in a sheet as the 8T-7765 Hand Pad.1. Place a 38 mm (1.5 in) square piece of "Scotch Brite" material on the end of a 9U-6862 Small Tapered Brush. The carbon in the cylinder head bore for the unit injector is not as difficult to remove as carbon in locations that are exposed to higher temperatures. The use of a power tool to rotate the cleaning material should not be necessary.2. Use a 4C-5027 Tap Wrench to hold the brush. Rotate the material against the lower surface of the cylinder head bore for the unit injector. Continue cleaning until the surface is smooth and shiny. To clean loose particles from the cylinder head bore for the unit injector, the 4C-6774 Vacuum Kit Gun is recommended. The tool is operated with compressed air.3. Remove all of the loose particles from the entire cylinder head bore for the unit injector.