Front Main Seal
An oil seal located at the front of the crankshaft that prevents oil from leaking out of the timing cover area.
The front main seal (also known as the front crankshaft seal) is located at the front of the engine block, surrounding the nose of the crankshaft where it extends through the timing cover to drive the harmonic balancer and accessory belts. This seal ensures that engine oil remains sealed within the timing cover or oil pan while allowing the crankshaft to spin.
Front main seals are typically made of synthetic rubber or Teflon. Over time, heat cycles, engine vibration, and dirt contamination wear down the sealing lip. When the seal fails, it creates an oil leak that coats the front of the engine, the harmonic balancer, and the drive belts. This oil contamination can deteriorate rubber belts and cause them to slip or snap, leading to secondary failures of the alternator, water pump, or power steering.
Replacing a front main seal requires removing the accessory drive belts, the radiator fan, and the harmonic balancer. In many cases, particularly on engines with timing belts, the timing cover and timing belt gears must also be removed, making it a good practice to replace the front main seal during a timing belt service.