Rear main seal direction?

[ToddK]

I'm a bit confused about which direction the rear main seal should face. The seal I have, when looking at it in side profile, has a vertical face and a diagonal face on the section leading to the contact point on the crank. My best guess is the vertical side should face in towards the engine. Is this correct, or is my thinking 180 degrees wrong?

[jayb]

That is correct, the vertical face of the seal should face in towards the center of the engine.  Think of it from a crankshaft pressure perspective.  If there is pressure in the crank, and you had the seal installed the other way, it would be easier for the pressure to force its way past the seal.  Installed correctly the pressure in the crankcase helps push the seal against the crank's sealing surface.

[ToddK]

Thanks Jay, I just needed confirmation from an experienced engine builder.