Felt on front of crank seal

[Haz87]

This is the kind of question I thought I'd be able to get out of google, but all I keep getting is info about full felt seals.

Can someone explain why a crank seal would have a small felt ring bonded to the front (external) of it?

Like this:

To be clear, the felt does not run through the seal, its just a piece attached to a common design rubber seal. What benefit does this offer?

 

[Screwdriver]

My guess is it's for a two stroke engine, so it holds oil.

 

[voipio]

The felt ring is referred to as a dust lip, and seems to be intended to trap, and prevent dust from finding its way to the sealing surfaces. It can also retain a small quantity of oil, which helps to prevent the oil in the seal from "drying out" and degrading the o-ring performance.

 

[Haz87]

My guess is it's for a two stroke engine, so it holds oil.

The one in the pic is from a Ford zetec engine (Escort,Mondeo etc)

 

[Haz87]

The felt ring is referred to as a dust lip, and seems to be intended to trap, and prevent dust from finding its way to the sealing surfaces. It can also retain a small quantity of oil, which helps to prevent the oil in the seal from "drying out" and degrading the o-ring performance.

The dust/debris prevention makes sense. On the oil retention for protection front, its only going to get oil on it when the seal is already compromised so seems a bit redundant.
Appreciate the input