Oil Leak 08 Yz450f Help!!!!!!

[08YZ450Derek]

Man, I might of just screwed something up. I took off my countershaft sprocket, and started my bike without it on. 20-30 seconds later oil was shooting out of the countershaft area. What the hell happened? Does the countershaft sprocket serve as a seal when bolted on the bike to keep oil from coming out of there? Please help!!! I shut it off right when that happened. It only leaked out maybe 1 1/2 oz of oil.(small puddle).

To add: I had one hell of a time removing the sprocket. It was rusted on, I had someone hold the rear brake and I got it off. The bike did not leak until started.

I checked it just now and its leaking slowly. Tilt the bike and it leaks. Im thinking that the countershaft seal is shot. I will need to replace it, please tell me there is a way with out splitting those cases. Thanks in advance.

[grayracer513]

Not sure why you would run the engine with the front sprocket removed and the bearing exposed, but what you saw was normal. The YZF transmission is pressure fed oil by the engine oil pump. The oil is delivered to the left side trans bearings, where it enters each shaft and is fed across to the other end. With the sprocket removed, the oil pressure will push the sealing collar out a little and pump oil on the ground. If the seal didn't leak before you pulled the sprocket, there's no reason to think it will now if you haven't messed with it directly. At least you know the oil pressure is OK.

In the future, lay a hammer handle or sturdy board across the swing arm through the spokes as near the rim as possible with the chain on to hold the sprocket from turning while the nut is removed.

[08YZ450Derek]

I did not think of that method. I will remove sprockets like that from now on. I did not know that removing the countershaft sprocket exposed anything, or I would not have started the bike. Im so new to 4 strokes.

The seal did not leak before the removal of the sprocket, and I did not mess with it. So, will it be okay when I put my new sprockets on? I ran the bike because I just checked my valves and wanted to make sure nothing was wrong.

Thanks, from a Veteran.-Derek

[grayracer513]

I did not know that removing the countershaft sprocket exposed anything, or I would not have started the bike.

Thanks, from a Veteran.-Derek

Thanks from a Marine Dad for being a Veteran.

Even with a two-stroke, or a four stroke with a more conventional "splash lubed" trans, when the engine runs, the shafts turn, and when the shafts turn, by design, they move oil up onto the bearings. Don't be too surprised if this happens with any bike.

[08YZ450Derek]

I thought at first I had damaged the seal somehow when I took the sprocket off. But I have changed a few sprockets and I never had any problems. I def learned something new today!

Should the seal go back to normal when I bolt up the new sprocket? And if these seals go bad, do you have to split the cases to repair? Or do you remove the old seal and press a new one in? Thanks:thumbsup:

[yamadog48]

no you dont have to split the cases to remove the seal just a pick or somthing pretty small and it will pop right out!!