Rear Main Seal - SBC 400 Align Hone & Alm Block

The Rear Main Seal - SBC 400 Align Hone & Alm Block by Cometic Gaskets is a precision-engineered two-piece rubber seal designed for Small Block Chevy 400 applications requiring align honed or aluminum block compatibility. This component prevents oil leakage at the engine's rear crankshaft position, a critical interface where factory seals often fail under sustained performance or high mileage conditions. Rebuilders, engine shops, and performance enthusiasts rely on this seal when restoring or upgrading Small Block Chevy 400 blocks to OEM or better-than-OEM standards.

Cometic's two-piece design offers superior sealing geometry compared to one-piece alternatives, accommodating the dimensional variations introduced by align honing operations on 400 blocks. The rubber compound is formulated to resist oil degradation and thermal cycling, maintaining elastic memory across extended temperature ranges typical of street and mild racing engines. The align hone specification ensures this seal will fit correctly on blocks that have been machined to restore roundness and concentricity at the rear main bore—a common practice during rebuilds to eliminate oil weeping and improve longevity.

This rear main seal is ideal for engine builders completing a full Small Block Chevy 400 overhaul, whether in a street car, restomod, or performance application. It is sold individually and must be paired with a new crankshaft rear flange assembly during installation. Proper seating requires careful alignment during final assembly and adherence to torque specifications for the crankshaft bolt. Installation is straightforward for experienced builders; consult factory service manuals or Cometic technical resources for detailed procedures and torque values specific to your 400 block variant.