Uh no! BIG oil leak.

There is a big oil leak on my '03. The circle of oil that has leaked out is about 6 inches in diamter. It is leaking on the left side of the motor at the bottom. It is kinda weird, because there is oil all around the front sprocket and on the chain. But the most oil is around where the shifter goes into the motor. There is oil from 1 inch in front of the front sprocket to the very back of the motor. There is also oil just below the clutch cable. Is this just a o-ring around the shifter gone bad is or is it worse? Am I looking at a major repair?

There are 3 possibilities. 1, the shifter shaft seal. 2a, the countershaft seal, 2b, the countershaft collar O-ring.

First, clean everything up and see if it continues to leak while it's sitting. If so, it is almost certainly the shifter seal, which is replaceable by removing only the lever.

If it does not leak while sitting, it's probably the counter, or output, shaft seal and/or the O-ring on the shaft. Go to the Yamaha Parts Catalog (if you see the "My Yamaha" page, click "proceed to catalog"), put in Motorcycle, 2003, & YZ450. When the fiche loads go to the transmission page. Look at #21, 22, & 23 in the illustration. 21 is the seal, 22 is the collar on which the seal lip runs, and 23 is the O-ring that seals the collar to the shaft. These can all be replaced from the outside with the front sprocket removed. The collar may not be needed, but if it is grooved, replace it.

Thanks! :thumbsup:

that's it exactly. How do i get the counter shaft seal out to replace?

Pry the seal out with a screwdriver, carefully. It may help to pull the collar the seal rides on off of the counter shaft, too, and to do that you may have to turn it as you pull outward. Inspect the collar and replace it if it has a pronounced groove worn into it by the seal. There is an o-ring under the collar that seals between the shaft and collar that should be replaced as well.

Thanks, I just noticed this same problem on my 05 yz450. :)

Oh god countershaft seals, if you do replace it yourself, make sure you buy at least 2 of them. They are difficult to seat properly, and if you do it wrong it will leak when you run the bike again. When removing the old seal, be extremely careful if using a screwdriver, I managed to score the case wall a tiny bit and had to sand it down and that was not easy. When seating the new seal, use a piece of PVC pipe and lightly tap it with a mallet until it is "proud". Not fully tapped in, or it will leak! I had so much fun learning this!:)

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