Unprovoked Unidentified oil leak, stumped.

8 replies to this topic
  • c5speed

Posted June 11, 2008 - 05:56 AM


I was out riding supermoto on my 07 yz450f yesterday with my dad. We came to a stop light and he pointed out I was rapidly losing oil, so we pulled into a gas station and stopped, where my bike continued to lose oil fast. It wasn't squirting out, but it was a fast leak. The bike didn't overheat, run bad, or lose compression at all, it just started barfing oil everywhere. It seemed to be coming from somewhere around the neutral switch.

When i got the bike home I drained the rest of the oil out of it, refilled it and ta da! No leak, at least not at idle or revving. I can't figure it out but I dont want to ride it til I figure out why and where it was leaking. Any ideas?:thumbsup:

  • matt4x4

Posted June 11, 2008 - 07:23 AM


Sounds like your countershaft seal.

Remove chain, remove front sprocket, remove 2 8mm head bolts, remove seal cover, check seal.
If the seal or collar (metal ring inside seal) are damaged, you'll have a leak.
Replace seal, collar and oring (behind collar on shaft) as a set.
While it's apart, fell for side to side play on the output shaft bearing by moving the shaft end sideways up/down. Having play there is NOT good.

  • c5speed

Posted June 11, 2008 - 08:13 AM


I removed the chain and sprocket but not the seal cover, I'll try that tonight but I dont think it's that seal because there isn't any oil around the shaft or seal cover.

  • grayracer513

Posted June 11, 2008 - 08:38 AM


Your first step is going to have to be to identify where the oil was coming from, and to resolve the apparent non-sequitur that it leaked that much oil, but no longer does so. It should have left some kind of trail.

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  • matt4x4

Posted June 11, 2008 - 09:29 AM


Ok, left side of bike, down low....

your vent from the head comes out in front of the shifter on the frame, just wouldn't have a clue as to how it would send a ton of oil up and out your head unless the oil could not drain from the head......

Best thing is to look for the high point where oil will be on the case - it's likely that at or near this level, your leak exists...

Shifter seal - potentially yes

Countershaft seal - potentially yes

Neutral switch - has an oring but for that to break and leak lots of oil the neutral switch itself would have had to crack open.....

Stator Cover gasket - highly unlikely

Drain plug - potentially yes

  • grayracer513

Posted June 11, 2008 - 10:20 AM


Most of what you listed fails the test of logic imposed by the fact that it did leak, but now doesn't, unfortunately. There are two points that you omitted:

> The overfill check/drain bolt, located behind the neutral switch (8mm head, copper washer, see the manual under oil change procedure)

> Passageway plugs (2) in the ignition cover that plug the open ends of the drillway used for return oil.

Both of these would also either leak or not, so they fail the test as well.

The breather seems the only one that fits that intermittent leak parameter. The usual cause of excesses of oil out of the breather is overfilling the system to the point that there is not room for the entire volume of oil in the oil tank. This causes the sump oil level to be excessively high, which in turn causes interference with oil draining from the top, and that leads to the excess being blown out the tube.

The usual way the bike is overfilled is either because the sump AND tank were not both drained during an oil change, or oil was erroneously added because the engine was not run prior to checking the opil level, and the dip stick reading was artificially low because of it.

  • c5speed

Posted June 11, 2008 - 10:50 AM


I did an oil change the day before, and I thought I overfilled it at first because when I checked it oil came out the oil tank cap. However when I stood it up straight it was just right on the dipstick. I did run the engine then let it sit for a few minutes before I checked it.

The breather does make the most sense, because there is no oil around any of the oil drain bolts, shifter, shaft, or stator cover, they are clean. most of the oil is around the neutral switch, below the primary drive sprocket. What I don't get is that it leaked at the end of the ride, we were on our way home after about an hour up and down a canyon and it didn't leak anything while riding there.

While in the canyon I didnt really get out of 2nd gear, really tight stuff. Once I was out though, I did nearly max it out in 5th. Could it be that I just overfilled it and the oil pressure got high enough to blow it out the overflow during my little sprint?

  • matt4x4

Posted June 11, 2008 - 11:50 AM


looks like that did end up being your problem and thanks to gray who explained it very well on how it can happen... esp. if overfilling.

By the time you stood the bike upright etc - probably, much of the overfilled oil drained to the sump so it looked good on again the stick.

Gray - I agree most of what I listed fails the leaked but now doesn't logic, I was mainly just creating a list off hand of what I am aware of on that side that can just start leaking, I've seen shifter seals leak but stop, so the countershaft seal would fall under the same scenario - of course, never seen them leak huge amounts then stop...

as for the drain plug - he would have had to remove that to change the oil once home, this would leave the plug in a tampered state, possibly fixing the leak it may have had.....

  • grayracer513

Posted June 11, 2008 - 11:53 AM


While in the canyon I didnt really get out of 2nd gear, really tight stuff. Once I was out though, I did nearly max it out in 5th. Could it be that I just overfilled it and the oil pressure got high enough to blow it out the overflow during my little sprint?

The breather is open to the air volume contained within the engine, and has no way of being able to sense any change in oil pressure. However, high rpm and throttle loads increase crankcase air pressure, and increase the volume of oil droplets in the crankcase air as well. Both of these things will increase the tendency to expel oil from the breather tube. If it were also slightly overfilled, it could have been less obvious at low speeds than high.

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