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What is the source/cause of this leak?


alextstone

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I did my first oil change yesterday.  I found several concerning issues.  Because they are different in nature, I will post them separately.  The first one is wha appears to be an oil leak near the exhaust flange of cylinder 4.   It drips right onto the v-band clamp.  The cylinder has 90 hours in service, clean as a whistle inside (, third photo).

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Every Lycoming I have ever owned did that at one time or another. It usually comes from the intake tube. It is probably running over to the exhaust. Replacing the intake gasket is probably your best bet. Some people on here are neurotic about tiny intake leaks, I don't think they matter much.

These engines don't have valve seals, any oil that makes its way past the valve stem while the engine is running just gets burned. After shut down there is still residual oil in the rocker boxes. a small amount runs down the valve stem and then drips on the side of the intake port. If you have a good intake gasket it will run down into the sump and eventually out the sniffle valve onto the ground. If the intake gasket isn't perfect, some will run out where you see it. The exhaust valve is kind of self sealing because of deposit buildup, so you don't see it as much on the exhaust side. 

The only bad effect from this is cosmetic.

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5 minutes ago, LANCECASPER said:

It could be the cylinder drain tube fitting (blue), but most likely on the Bravo it's one of the many oil line fittings on top of the cylinders leaking and the oil traveling down through the cooling fins. These seem to loosen up on their own.

1691066964_ScreenShot2019-01-20at8_38_39AM.thumb.png.1037b846398fab0e84d02b254ac97042.png

 

Thanks, headed out to the airport now... I’ll check that.  What do you think would be safe to use to clean that oil off the v-band?

 

 

 

 

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Lance is right about the pushrod tubes. They are kind of a crappy design and they leak a lot. They are a pain to fix because you have to take the rocker arms off. 

Once again this is all cosmetic. That baked on oil crud will need to be scraped off mineral spirits will be pretty slow on that stuff, MEK would be better. You might try a Dremel wire brush. 

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You can just name your oil leaks and make friends with them.
If someone asks about some oil on #3, just say "That's Henry, he likes to come out and play some times" 


And let’s not forget Frankie (the bottom seal for the oil dip tube).




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The MSC called it a leak from the Bravo oil lines, which changed the model from TLS to Bravo. So I have no clue the name of the lines. ln Lances pix above there the little metal tubing above the cylinders. In the first photo depicting the dried up oil on the flange, that’s exactly where mine leaked, when I brought it in I mentioned I thought I had a push rod leak they noticed the gooky flange and said it’s leaking on the Bravo fitting, they were correct.

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The MSC called it a leak from the Bravo oil lines, which changed the model from TLS to Bravo. So I have no clue the name of the lines. ln Lances pix above there the little metal tubing above the cylinders. In the first photo depicting the dried up oil on the flange, that’s exactly where mine leaked, when I brought it in I mentioned I thought I had a push rod leak they noticed the gooky flange and said it’s leaking on the Bravo fitting, they were correct.


LOL! We were asking about naming leaks. How about we call this one Billy?


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Oil must get out. It is its mission!

If you stop one leak, it must find another way out!

It is like a Navajo rug. They always leave a small flaw in the weaving to let the evil spirits out. If you have a small oil leak just let it be. It will make the oil happy. If you fix the small leak it will make the oil mad and it will cause a big leak!

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The biggest challenge with oil leaks is that even the smallest leak can spread everywhere and make it impossible to find the real leak. You can have some success by cleaning off the engine and watching it like a hawk. I don’t think there has been one annual where I don’t see some sort of oil leak being addressed.


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On 1/20/2019 at 7:46 AM, N201MKTurbo said:

After shut down there is still residual oil in the rocker boxes. a small amount runs down the valve stem and then drips on the side of the intake port. If you have a good intake gasket it will run down into the sump and eventually out the sniffle valve onto the ground.

As a person currently chasing what appears to be oil leaking out of an intake tube gasket, I'd like to understand this better.

First, any way to differentiate an innocuous leak caused by a tiny dribble through a good valve guide, from a disconcerting larger leak caused by a valve guide that's starting to go bad and which might fail the wobble test?  I'm hoping ours is a combination of the former plus an intake seal that's aging.  But I have to account for the possibility the intake seal is about the same as it's always been, and the leak through the valve guide is getting worse.

Second, when you say the oil runs "into" the sump, you just mean the intake tube portion of the casting assembly that contains the sump, right?  I don't mean to nit-pick, just want to clarify for myself and others that oil in the sump never comes directly in contact with any intake tubes.  Below is a picture of what people commonly call the "sump" on a Lycoming IO-360.  Air from the throttle body passes through the bottom portion of this casting before entering the individual intake tubes for the cylinders.  It's warmed by hot oil in the reservoir at the top of the casting, but there's no direct path from the reservoir to the intake plumbing unless the casting is cracked.  I assume the sniffle valve is at the bottom of the intake passage in this casting?

s-l1600.jpg

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43 minutes ago, Vance Harral said:

As a person currently chasing what appears to be oil leaking out of an intake tube gasket, I'd like to understand this better.

First, any way to differentiate an innocuous leak caused by a tiny dribble through a good valve guide, from a disconcerting larger leak caused by a valve guide that's starting to go bad and which might fail the wobble test?  I'm hoping ours is a combination of the former plus an intake seal that's aging.  But I have to account for the possibility the intake seal is about the same as it's always been, and the leak through the valve guide is getting worse.

Second, when you say the oil runs "into" the sump, you just mean the intake tube portion of the casting assembly that contains the sump, right?  I don't mean to nit-pick, just want to clarify for myself and others that oil in the sump never comes directly in contact with any intake tubes.  Below is a picture of what people commonly call the "sump" on a Lycoming IO-360.  Air from the throttle body passes through the bottom portion of this casting before entering the individual intake tubes for the cylinders.  It's warmed by hot oil in the reservoir at the top of the casting, but there's no direct path from the reservoir to the intake plumbing unless the casting is cracked.  I assume the sniffle valve is at the bottom of the intake passage in this casting?

s-l1600.jpg

Yes,

It drains into the area where the intake tubes go, not where the oil is.

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I was taught years ago to start an annual by protecting the mags and other electronic components and spraying down the engine compartment with Gunk. Let sit about 15 minutes and thoroughly rinse with water hose.

Caveat, that was 40 years ago and might be unacceptable now in some jurisdictions.  

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