Countershaft Seal Dilemmas

Hey guys I replaced my countershaft seal roughly 15 hours ago on my 03 yz450f. The problem is its already leaking again. I only replaced the seal. My question is should I replace anything else along with the seal again? Any input is appreciated, thanks guys.

There are 3 components that can cause that repeated leak.


One is the O-ring under the collar that slips over the output shaft.  This keeps oil from working between the shaft and the collar, then out between collar and sprocket.  Another is the collar itself.  If there is a distinct groove worn into it by the old seal, it needs to be replaced, as the groove will "trap" the seal lips and prevent them from following the collar surface correctly.  If you can feel the groove with a fingernail, it's probably too big.


Then there is the seal.  The seal pocket has no "bottom" to seat the seal against; it's bored straight through.  That means that the seal can easily be inserted on a tilt, and that it can be inserted too far.  If it's tilted excessively, it looks like an oval shaped hole to the round collar, and won't seal effectively.  If it is inserted too far, it will expose the notches on the inboard end of the collar and allow oil past the seal.   The seal should stand .5 - 1.0mm above the case surface when properly installed.

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