seal question

Oil, or a grease that disolves in oil. Usually its just plain ol oil.

 

Never, ever dry --- they will likely get damaged as soon as the axle spins a few revolutions --- always pre-lubricate the sealing contact area against the axle.

 

Obligatory "blew a seal" joke.

 

I've used assembly lube to good effect with seals.

 

That's what I use too.

 

At the OP ---

Also, if you were perhaps referring to the external (seating surfaces) of the seal --- as opposed to the contact area against the axle --- it is good to smear that lightly with motor oil as well as it makes it easier to insert and keeps it from getting abraded or gouged when pushed into the recess / seat.

 

For the rubber shaft side (inner surface), I always use synthetic grease. It’s safe to mix with all oils and prevents tearing and heat damage after first startup.

For the outer edge that mates to the metal pocket, it really depends on the mechanical fit, and the materials. If you have a proper service manual it will actually indicate whether to use oil, grease, or keep dry. Sometimes it will specify a low, medium, or high strength thread lock as is the case with a prop seal on an outboard engine.

As a rule of thumb, if the seal has an outside metal housing then always wipe it down with oil along with the engine side and then wipe both very dry. This cleans the surfaces removing any past corrosion or adhesives. If it is a loose hand fit then I will use a low strength blue lock-tight. This keeps it from spinning inside the pocket. If it has a very tight hand fit or will not fit by hand then they go in lightly oiled after heating the engine pocket slowly with a propane torch while cooling the seal in the freezer. This will allow the seal to fit snugly and deter corrosion.

Good luck.