Seal direction

Does anyone know what direction the main shaft oil seal goes? It's the one behind the washer and c clip in the outer clutch case.

#15 is the one I'm referring too.


Open spring side goes up facing installer.


*edited to correct info*





Edited by Zaj 243

That one goes in open side up toward you as you install it.


Simple rule with all OEM Yamaha seals is that the numbers on the seal face up toward the installer.  This one's no different.


I know what you're thinking; "It looks backwards", right?  Seals always face the fluid they seal, no?  No, not here.  The seal is reversed from normal for good reason.  The seal carries lube system oil under pressure from the pump to the crank in order to feed the rod bearing and the cylinder walls.  If the seal were turned around facing the lube system oil pressure straight off the feed pump, with only splash to lube the outside of it, running against the nose of the crank turning 11,000 RPM would produce significant wear on the nose of the crank axle, and might well scorch the seal under the wrong circumstance.  The way it is lets oil blow under the lips of the seal, forming an oil bearing of sorts, and at the same time acting as a low rent pressure regulator. 

Don't the water pump seals go open side up when installed?

Gray, I have to say that I appreciate the way you answer questions with an explanation of why things are done the way they are instead of just a yes or no or a right or wrong. I applaud you and appreciate your vast knowledge.

Don't the water pump seals go open side up when installed?

Yes they do, but in that case, the seal lips are oriented toward the fluids being sealed; the oil seal faces against the oil

In the crankcase cover, and the coolant seal toward the coast in the water pump. So they seem logically placed like that.

Until you understand that the lube seal on the crank is supposed to leak, that one seems wrong when you look at it simply as a sealing device. The layout bugged me for a long time.

Thank you, I appreciate the time you took in answering my questions. I'm glad to hear I'm not the only one who was thrown by this hahaha.

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