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YZ125 coolant in trans oil--possible routes?

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My 2006 clearly has water/coolant in the oil again.  This happened once before and I replaced the right side case gasket for the fix.  Apparently the gasket failed allowing coolant to seep from coolant passages into the transmission.   I know that it's not the usual water pump seal(s) issue (common on other bikes), as my 125 has the "air gap" design between the oil and coolant seals at the water pump, and nothing is coming out the weep hole.  Are there any other contamination routes I'm overlooking?  Thanks!

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None that I can think of. However, I have seen bad castings where there was a very small passage way that allowed a cylinder to leak oil on a big 4 stroke. That would not be to likely, but something that "could" happen.

The bike was a 2013 Beta 498, and it was bleeding out the side of the cylinder. Probably could have just peened it a few times but Beta replaced it under warranty. This was an external thing, and we are talking internal on yours (if thats the case). You and I know it is highly unlikely that water/oil contamination can happen through the seals on the water pump. 

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Another thing I will add..

Is it coolant or water? 

If you do a lot of water crossings a hot engine hitting cold water can contract, and the breather tube than sucks up a little water. Multiple water crossings with hot engine, multiple contractions and sucking. 

Just a thought. 

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Thanks for the thoughts!  No water crossings, but just prior to this scheduled transmission oil change (every 15 hours), two things happened:

1. I replaced the piston ring on my regular schedule, so the top-end was open.

2. I had a big crash that totally pretzeled the left side radiator.  I had just reinstalled the Myler's repaired radiator (they do GREAT work!) and took the bike for a test ride.

However, I can't think how either of these two things could have resulted in water getting in the transmission oil.  Am I missing something?

Edited by rpt50

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1 hour ago, rpt50 said:

Thanks for the thoughts!  No water crossings, but just prior to this scheduled transmission oil change (every 15 hours), two things happened:

1. I replaced the piston ring on my regular schedule, so the top-end was open.

2. I had a big crash that totally pretzeled the left side radiator.  I had just reinstalled the Myler's repaired radiator (they do GREAT work!) and took the bike for a test ride.

However, I can't think how either of these two things could have resulted in water getting in the transmission oil.  Am I missing something?

No way for coolant to enter in either 1 or 2... Puzzled.. 

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The only way for coolant to enter the clutch case is through the 2 oil seals. A worn bearing could make the shaft wobble slightly and let water through. If you replaced the seals without polishing the shaft those seals will not hold.  

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51 minutes ago, arnego2 said:

The only way for coolant to enter the clutch case is through the 2 oil seals. A worn bearing could make the shaft wobble slightly and let water through. If you replaced the seals without polishing the shaft those seals will not hold.  

If the outer right case gasket blows out. If I use an old one (and I have on my bike about 3rd time) I run a small film of yamabond just around the gasket on both side where the water jacket passes. Had no leaks and have been successful. 

Honestly, that and what I mentioned about a bad casting can be the only way for coolant to exchange with the trans oil. 

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1 hour ago, arnego2 said:

The only way for coolant to enter the clutch case is through the 2 oil seals. A worn bearing could make the shaft wobble slightly and let water through. If you replaced the seals without polishing the shaft those seals will not hold.  

This is the usual cause on most motorcycles, but I don't see how this can happen on a YZ due to the design with the gap between the seal that keeps the coolant in place, and the seal that keeps the oil in place.  Nothing is visible in the weep hole.  

I'll just replace the right side gasket again, maybe this time with a little gasket sealer.  I think the last time this happened was about a year ago.  Maybe I can get a little more life with some sealer. 

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22 minutes ago, rpt50 said:

This is the usual cause on most motorcycles, but I don't see how this can happen on a YZ due to the design with the gap between the seal that keeps the coolant in place, and the seal that keeps the oil in place.  Nothing is visible in the weep hole.  

I'll just replace the right side gasket again, maybe this time with a little gasket sealer.  I think the last time this happened was about a year ago.  Maybe I can get a little more life with some sealer. 

Once you get it off, put it on a plate of glass with a little oil around the edge and see if there is a slight warp you can see. Just a thought.

 

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When you get it off, look for a gouge or scratch around that water jacket on each side of the gasket. Strange, I've had my right side case on and off a lot with the same gasket, never a problem.

 

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There is an oring between the case halves also (same channel that was leaking on your right case)

 

never had one leak but every time I split the cases I make sure I goop extra case sealer around that area.

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3 hours ago, qwert321 said:

#16 in the image 

 

 

only other route I can think of 

IMG_1342.PNG

It's a good thought, but the coolant will never make it to the transmission if that leaks. Just an FYI. 

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