Rear Main Seal SBF 351W 69-83 2pc Viton

The Rear Main Seal SBF 351W 69-83 2pc Viton from COMETIC GASKETS is a precision crankshaft seal engineered for classic Small Block Ford engines, particularly the 351W platform produced between 1969 and 1983. This two-piece design addresses one of the most critical sealing points in any engine—the junction where the crankshaft exits the block at the flywheel. Mechanics and engine builders rely on this seal to prevent oil leakage that can compromise performance, contaminate the transmission, and lead to expensive repairs if left unchecked.

Constructed from Viton elastomer material, this rear main seal delivers superior heat and oil resistance compared to traditional Buna-N compounds, making it ideal for high-output or modified engines that generate elevated operating temperatures. The two-piece construction allows for installation without removing the crankshaft—a significant advantage over one-piece designs that demand complete engine teardown. Viton's chemical stability ensures the seal maintains its compression set and flexibility across extended temperature ranges, preventing the hardening and cracking that leads to seepage in aged seals. The precision fit (6.05 x 0.3 x 7.15 inches) ensures proper bore engagement and eliminates the wobble that causes premature wear and leakage.

This seal is essential for anyone rebuilding or refreshing a 351W Small Block Ford, whether for a classic muscle car, street rod, or performance-minded daily driver. Installation during a pan-off service, transmission removal, or full engine rebuild ensures your crank stays sealed without oil weeping onto the bell housing. The Viton material is particularly valued by restorers and tuners who plan to run ethanol blends or operate their engines in demanding conditions, as it outperforms budget alternatives over the long term and reduces the risk of comebacks.