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  • On 4th June 2017

Crankshaft oil seals for HONDA CB550.  OEM or aftermarket?  How do you decide?  The debate about OEM vs. aftermarket will probably never end.  And for good reasons.  While OEM parts will always work as intended, in the case of vintage motorcycles OEM parts the materials they are made from may not be as good as their modern counterparts such as, for example, friction materials like shoe pads or brake pads, or O-rings, or lubricants.  My personal approach in most cases is this: If it is a moving part, get OEM and if it is not a moving part, consider the aftermarket replacement.  (Note that I did not say the aftermarket equivalent.) But the true answer to the question, as always, lies in understanding what the part in question does, how it does what it does, and what is the differences between the OEM and the aftermarket parts.  Once that is understood, the question becomes easy to answer.

Take the crankshaft oil seals for example.

The crankshaft rotates around these seals 1,000 times every minute when the engine is idling.  When you are riding along, the engine is probably averaging 5,000 RPM.  For every hour you are on the road, the crankshaft will have rotated around the oil seal 300,000 times.  And if you are averaging 40 miles per hour, by the time you have clocked 40,000 miles the crankshaft will have done 300,000,000 revolutions around that seal.   Three hundred million!  Apparently, the HONDA designers thought that only a very special seal can take this kind of abuse.  So, they designed it very differently from an ordinary oil seal.

Let’s take a look.  Here are both seals, back side:

And here is a closer look of both seals, front side.  Note the arrows telling us that these seals are directional.  But we need to look closer, much closer to see how they differ from ordinary oil seals.

Okay, let’s zoom in.  Here is what the genuine HONDA seal on the alternator side looks like.

And here is what the genuine HONDA oil seal on the points side looks like:

Note the rib design.  And note that the rib pattern is different from one seal to the other.  Obviously, the HONDA designers had very good reasons for putting these seals in even though they are more expensive to make than other ordinary non-directional oil seals such as the aftermarket ones you can buy for your CB550’s crankshaft.

So what?

Well, replacing most of the oils seals on your bike is relatively simple.  Replacing the crankshaft oil seals, if they started to leak, requires taking the whole engine apart all the way to the very bottom since putting new crankshaft oil seals in necessitates removing the crankshaft itself.

Buying cheaper OEM parts in the belief that they are “just as good” as the OEM parts is something we have all done.  Why spend the extra money, right?  Right.

Until you end up rebuilding your engine for the second time to replace the aftermarket oil seals because they started leaking  in which case you’ll say to yourself, like I did, “Never again!”.