BEARING AS-ROLLER 5P3930 - Caterpillar

1.1 Liter Family Of EnginesIn some cases the deterioration of the 328970 O-Ring Seal at the bottom of the unit injector has been reported as the cause of combustion leakage around the injector. The purpose of this seal is to provide initial sealing until the unit injector seats in the 7W5749 Sleeve (brass) in the cylinder head. The injector seats in the sleeve almost immediately after the initial engine start up. Therefore, deterioration of the 328970 O-Ring Seal will not result in combustion leakage. It is normal for this seal to deteriorate over time due to exposure to the hot combustion gasses.
Whenever the unit injector is removed, both the tip and body seals should be replaced. The seating surface of the brass sleeve should be inspected and replaced if necessary.
Location of the 328970 O-Ring Seal (tip).