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Oil seals

Practical Engine Building

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In a installing Crankshaft Oil Seals part of course you say that lubricating outside surface of the oil seal is detrimental. Why is that a bad idea?

Thank you


It's more a problem with the type with the rubber on the outside, than the metal type, but even the latter may have problems.

If you think for a moment, when you apply a lubricant on the outside and/or in the bore it's going into, you're putting a thin layer of lubricant between the seal and it's bore. This thin layer of lubricant prevents the seal griping the bore properly and allows the seal to slide out on the layer - this is made worse when there is crankcase pressure also pushing it out.

Some sealants, especially the non-setting type, can have the same affect with the seal being squeezed out on the layer that's still liquid. that said, if the housing has been damaged, or I suspect there will be leakage around the seal, I have been known to use Shellac, which is a hard setting sealant that will grip the seal.

Don't forget to lightly lubricate the seal lips - if they're run dry against a shaft there can be rapid failure from wear and even melting of the lip from heat build up.

Thank you very much for your answer and your advice.

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