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Transmission oil breather leak

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Hey guys, I have an 07 crf250r that started puking oil out of the transmission breather tube after a short ride around the cul de sac and then letting it idle in the garage. I’ve put about three hours on it with the same oil so no recent changes in oil capacity. I’m going to check my crank case breather hose tonight to check and see if there’s a blockage causing excess pressure but I didn’t know if this was a common thing.

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Is the engine oil level decreasing?

Best to drain & measure the trans oil to see just how much is in there first.

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Is the engine oil level decreasing?

Best to drain & measure the trans oil to see just how much is in there first.

That’s one of the things I’m going to do tonight. Drain and measure both and refill to correct specification.

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Definitely had too much oil in the trans side. Not much on the engine side. No blockage from the breathers that I could see. Refilled oil and ran it for about 15 mins with a short ride and it still reading on the dipstick and no oil leaking out of the hose. The rate it was leaking the other day I would have expected it to start leaking again by now

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Yep sounds like a worn main seal causing oil migration. Pretty common.

Plenty of threads on this to read up on.

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I guess I’ll be replacing all the seals I can with out splitting the cases. Definitely no blockage in my vent hoses or in the valve cover. I put about a half an hour on it today checking the dipstick level periodically and never had a change. I don’t want something just letting lose tho and smoking the engine because I don’t notice a leak while riding

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15 hours ago, Loganclark73 said:

I guess I’ll be replacing all the seals I can with out splitting the cases. Definitely no blockage in my vent hoses or in the valve cover. I put about a half an hour on it today checking the dipstick level periodically and never had a change. I don’t want something just letting lose tho and smoking the engine because I don’t notice a leak while riding

Did you by chance drop the bike recently?

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Did you by chance drop the bike recently?

The last ride before I noticed the leak I was trail riding. Last 1/4 mile of trail I over shot the corner laid it over. It wasn’t violent, just didn’t get a good footing in the vegetation before I was too far over to stop myself. Could that have done it?

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1 minute ago, Loganclark73 said:


The last ride before I noticed the leak I was trail riding. Last 1/4 mile of trail I over shot the corner laid it over. It wasn’t violent, just didn’t get a good footing in the vegetation before I was too far over to stop myself. Could that have done it?

And sorry I should have asked this originally.

Which vent tube was it coming out of?

Was it actually tranny oil and when you say puking was it like an oz or more?

Did you measure tranny oil and fill the tranny side as per spec recently?

Did you drain and measure the tranny oil?

Are you 100% sure engine oil level is not dropping or increasing?

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And sorry I should have asked this originally.
Which vent tube was it coming out of?
Was it actually tranny oil and when you say puking was it like an oz or more?
Did you measure tranny oil and fill the tranny side as per spec recently?
Did you drain and measure the tranny oil?
Are you 100% sure engine oil level is not dropping or increasing?

It was definitely the trans vent tube coming from the right side of the engine on the lower case.
I had a bout a square foot of oil on the garage floor under the bike.
I had about four hours on the previous oil change so no recent changes.
Trans oil was about 400cc over spec after it already drained out of the vent tube.
I’ve put about a half hour on it since draining and refilling both engine and trans to spec but have not been able to measure a change in engine oil level on the dipstick. It’s stayed consistent through three heat cycles now.

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1 minute ago, Loganclark73 said:


It was definitely the trans vent tube coming from the right side of the engine on the lower case.
I had a bout a square foot of oil on the garage floor under the bike.
I had about four hours on the previous oil change so no recent changes.
Trans oil was about 400cc over spec after it already drained out of the vent tube.
I’ve put about a half hour on it since draining and refilling both engine and trans to spec but have not been able to measure a change in engine oil level on the dipstick. It’s stayed consistent through three heat cycles now.

I use 780ML on the tranny side so did you by chance over fill it?

If you can post a pic of the vent tube it was coming out of.

I dropped my bike once where it was almost upside down for a few minutes and engine oil vented into the air box and started dripping out. Not sure if this could happen on the tranny side but it MIGHT?

If your not losing engine oil IMO it's sort of a weird tranny oil issue but I am no means an expert.

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I use 780ML on the tranny side so did you by chance over fill it?
If you can post a pic of the vent tube it was coming out of.
I dropped my bike once where it was almost upside down for a few minutes and engine oil vented into the air box and started dripping out. Not sure if this could happen on the tranny side but it MIGHT?
If your not losing engine oil IMO it's sort of a weird tranny oil issue but I am no means an expert.

Well when I drained the engine and trans the engine side had almost no oil in it. Maybe 100cc.

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24 minutes ago, Loganclark73 said:


Well when I drained the engine and trans the engine side had almost no oil in it. Maybe 100cc.

Sorry I'll now bow out of this. Good luck and I would be interested to hear how this works out for you dude.

 

Edited by filterx

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It wasn’t down for long. Maybe ten seconds. And yes it’s engine to tranny side as far as I can tell. I’m gonna keep checking it and probably replace the seals for pm if nothing else.

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