Leaking CS seal

I have an '05 YZ450 motor with a counter shaft leak I cannot seem to stop. The bike had a leak there when I purchased it so I replaced the seal, collar and o-ring. First ride out it leaked again so I went back in to check my work, all looked normal, replaced the seal again and she's still leaking.

I've discussed this with the local shop mechanic and the previous owner and we've tossed around the usual ideas as to the culprit but I'm throwing this out to you guys for a broader perspective.

Just to eliminate some guesses right off the bat, the shaft has no lateral movement, does not appear worn at the o-ring divot and the case where the outside of the seal touches has no visible nicks.

And a little history; the bike has a 488 bigbore kit, no other engine problems and the CS seal was all original and never touched prior to this leak. Thanks for your input.

this might sound dumb but is your crankcase vent tube plugged, if so it may be building up pressure and causing the seal to leak. just a random thought

Need to see if there is anything riding up against it.

Should be able to take some 400 gritt emerypaper and polish it down.

You can take the spark plug out of it and then have someone use the kick starter to crank it over while you hold the paper on it.

i'd give the feller ya bought it from a good tongue lashin':smirk: sorry your havin such a hard time with it:ride:

i'd give the feller ya bought it from a good tongue lashin':smirk: sorry your havin such a hard time with it:ride:

No worries man, very minor problem for an awesome machine...still lovin' this bike. :worthy:

If you set the seal too deeply, the square notches on the inner end of the collar can sometimes extend out past the lip of the seal. To avoid this, set the seal so that it stands proud of the end of the bore in the case by about 1.5mm (.060"; 1/16").

gray,thats quite possible;i knew you'd come up with sumthin' i'd agree with sooner or later:D

If you set the seal too deeply, the square notches on the inner end of the collar can sometimes extend out past the lip of the seal. To avoid this, set the seal so that it stands proud of the end of the bore in the case by about 1.5mm (.060"; 1/16").

Doesn't the steel collar actually rest up against the bearing when it's properly installed? Then there's no way those notches in the collar are deeper than the seal is thick.

I'll give your idea a try but like I said it was leaking before anyone touched it so maybe the OEM seal had worked it's way in past the case's edge. With that in mind could an aftermarket CS sprocket be the culprit? Allowing it all to be torqued too far due to it being thinner and the seal getting pressed in farther?

You would think the notches would be set back far enough not to overlap, but I've seen this reported, so it's worth looking at, at least.

As far as the logic that it leaked before, and so on, it was old and used then, so it may have been leaking for any number of reasons and still be leaking for a different one now.

An after market sprocket would only cause a leak if it were so thin that the nut bottomed out against the shaft splines before drawing up the collar.

I'm sure that you've already checked, but the leak could also be coming from the neutral switch or the shift shaft. The important, and often most difficult thing about diagnosing oil leaks is pinpointing their exact source, and not to be mislead by oil blown/thrown from somewhere else. If you're pretty sure it's the output shaft, take it back apart and try to see why.

I took it all apart for the third time tonight and really inspected everything. The source is obviously the CS area, neutral switch and shifter seal are both free of oil and crud.

As I checked everything I noticed nicks in the case (probably from me using the wrong methods for seal removal the first two times) and sanded them out as best I could with 400grit paper. I then cleaned and dried everything and set the new seal in place with a continuous bead of Yamabond 4 around the outside edge (up against the newly sanded case edge). I also set the seal flush with the case edge this time and took care not to go all the way into the bearing.

I'm letting the Yamabond cure over night before I re-assemble and will see how she holds with this weekends ride.

First ride today since the last fix and she's holding.

Did about 45mi of single and double-trac plus a little motocross and not a drop of oil to be seen. :bonk:

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