The scoring (scratching) of a shaft seal O.D. is most likely to be caused by improper machining of the housing bore. A housing surface that is too rough or that contains burrs will abrade the O.D. A scored O.D. can also result if the edges of the bore have not been chamfered properly. Figure 237 shows an example of a seal with a scored O.D.

The optimal surface finish for the bore largely depends on the type of shaft seal in use. Generally speaking, seals with a rubber-covered O.D. can handle a rougher surface finish than metal O.D. seals, but a surface that’s too rough may damage the O.D. or prevent formation of a tight static seal. On the other hand, a surface that’s too smooth may make it more difficult for a seal with a rubber-covered O.D. to stay in place. While there is no accepted standard for minimum bore roughness, we recommend a roughness of at least 2.03 µm (80 µin) Ra. If the bore exceeds 2.54 µm (100 µin) Ra, then a rubber O.D. seal or use of O.D. sealant is recommended. Bore roughness should never exceed 3.175 µm (125 µin.) Ra.

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