Other important factors are ensuring the hardness and roughness of the shaft are correct. A shaft hardness of HRC 45 is recommended for a rubber sealing lip, with a roughness of Ra 0.4-0.8. A higher shaft hardness of HRC 60 and shaft roughness of Ra 0.1-0.4 is recommended for a PTFE lip.
Dynamic seals called bearing isolators are used to shield bearings from external impurities. They are revolving (rotor) and stationary (stator) elements. O-rings or strong seals are used in some bearing isolators, while they are constructed like labyrinths in others.
If the seal is being fitted to original equipment you may have some influence over the shaft and housing bore finish, but if you are replacing a worn seal you still need to take into account the condition of these 2 essential parts.
Oil seal type or shape
For a more detailed discussion of seal characteristics, please see the following:
Seal characteristics
Insert a tyre lever or large screwdriver into the starter aperture so that it jams in the teeth of the ring gear on the flywheel .
Slacken the alternator or dynamo adjuster and pivot bolts, push the unit inwards and ease off the drive belt. Remove the belt completely.