No Benefit to Lubricating Outside of Engine

by Roger Decker

There are four things you should do to prevent a split main seal from leaking. First, apply a thin layer of silicone to the O.D. of the seal. Be sure the surfaces are clean and free of oil. Second, position the seal segments over the seal flange for SBCs or in the seal groove for SBFs (see Photo #1), with about a quarter inch offset (see Photo #2). Make sure the sealing lip goes to the inside of the engine. Then, apply a thin film of engine assembly grease or engine oil to the I.D. of the seal to prevent burning at startup.

Photo #1

Photo #2

Finally, apply a thin film of Permatex High Tack adhesive sealant across the mating surface of the cap, from the seal to the cap register, to prevent leakage across that area. Again, be sure the mating surfaces are clean and free of oil (see Photo #3).

Photo #3

Note: On 400 c.i. SBCs that have the main bearing housing in-line honed, it will be necessary to use a special seal, Fel-Pro #2909 or Detroit #99011. The I.D. of the seal flange is significantly increased after the line honing operation and will not provide adequate support for a "standard" seal.

Roger Decker
Canton Automotive Machine Service