Head porosity found during annual

[Cruiser73]

I have a mid time O-360-A1D engine.  The IA doing the annual while checking for exhaust leaks found small pin hole porosity between the some fins near the exhaust port. The pin holes where found when my mechanic connected a shop vac to the exhaust pipe to pressurize the system and sprayed a soapy solution on the exhaust system to look for bubbles.  There were bubble between the fins and we confirmed several times by drying the areas and retesting. But all four cylinders have a similar amount of porosity in almost the same location and to me finding it on all four cylinders seems highly unlikely.  He believes these might be the original cylinders and they should all be replaced.  The compression was 79, 78, 78, 78 so I was please until the news that all the cylinders need replaced.  The Lycoming rep said porosity is bad which I understand but it is difficult to say how long this has been an issue.  Do I just do the cylinders?  Thoughts 

[carusoam]

Got pics?

Does exhaust escape from these pores?

Or anything else leak out or into them?

 

Lets see if @M20Doc is familiar with porous O360 heads…

Best regards,

-a-

[Guest]

It’s a common issue on parallel valve cylinders that have been rebuilt.  

[47U]

2 hours ago, M20Doc said:

It’s a common issue on parallel valve cylinders that have been rebuilt.

So what’s the worst case?  The head is weakened from porosity and a crack develops?  Or, more catastrophic, without any warning the head blows off?

[Utah20Gflyer]

Does the Lycoming Rep agree that all the cylinders need to be replaced?   You mentioned he said it was bad but if he hasn't already given you more specific guidance I would ask for more specifics.  If the Lycoming Rep concurs with the mechanic that they need to be replaced then I think that is your final answer.  

[Greg Ellis]

3 hours ago, M20Doc said:

It’s a common issue on parallel valve cylinders that have been rebuilt.  

This may be a stupid question, but does this condemn the cylinder(s)?  I know that compression isn't everything in the health of a cylinder but his reported compressions are quite good.

And what is the root cause of this on rebuilt cylinders?

[Cruiser73]

4 hours ago, M20Doc said:

It’s a common issue on parallel valve cylinders that have been rebuilt.  

This is common?  The Lycoming rep sounds like he had never heard about it but the rep isn't an un-intetested party.  He would need to CYA and would want more Lycoming parts purchased.  That is why I was asking the question here.  

 

1 hour ago, Greg Ellis said:

This may be a stupid question, but does this condemn the cylinder(s)?  I know that compression isn't everything in the health of a cylinder but his reported compressions are quite good.

And what is the root cause of this on rebuilt cylinders?

I guess I have the same question as Greg Ellis.  Does this condemn a cylinder?  Is it common is it something that can be monitored.  Or is it so dangerous it needs to be done NOW?

[Pinecone]

My question is the leak from the exhaust area past the valve or from the combustion chamber area.

If in the combustion chamber area, I would be worried.

Exhaust port area, concerned, but less worried.

Mainly due to the pressures in each area.

[Guest]

Cracks between the fins that leak or flange gaskets that leak are a problem that should be addressed.  Cracked cylinders need to be welded or replaced.

[Guest]

2 hours ago, Greg Ellis said:

This may be a stupid question, but does this condemn the cylinder(s)?  I know that compression isn't everything in the health of a cylinder but his reported compressions are quite good.

And what is the root cause of this on rebuilt cylinders?

Exhaust ports found with cracks during overhaul would routinely get welded, the welds didn’t last forever before cracking again .

[Guest]

3 hours ago, 47U said:

So what’s the worst case?  The head is weakened from porosity and a crack develops?  Or, more catastrophic, without any warning the head blows off?

I’ve never seen an exhaust port crack lead to failure, but then we replace them when the crack is found.

[PT20J]

I've never heard of pinhole porosity (but I haven't heard of many things ). It's hard to imagine what would cause a solid aluminum casting to become porous. What does happen is that heads can develop cracks, and the cracks are usually evident between the fins. Lycoming did have a bad batch of cylinder heads 2013-2015.

https://cessnaowner.org/faa-issues-bulletin-related-to-certain-lycoming-engines/

Skip

[MooneyMitch]

11 minutes ago, PT20J said:

(but I haven't heard of many things )

The more you know, the more you know you don’t know…… 

[Ragsf15e]

3 hours ago, MooneyMitch said:

The more you know, the more you know you don’t know…… 

Rumsfelt?

[DXB]

Wow - Interesting phenomenon I've never heard of or thought to look for.  I imagine these are overhauled, not first run cylinders?

I did find this article that is relevant:

https://www.sciencedirect.com/science/article/pii/S1350630719314232

It sounds like high porosity in the cylinder head aluminum is a manufacturing flaw that happens at the time of casting.  It's hard to believe that alone would cause the kind of air leak that your A&P observed though. Per the article, linking of the pores with microcracks predisposes the cylinder to head separation, which is obviously worth preventing.  I imagine the microcracks are what actually produce the visible leak?

I really have no clue how common this issue is or whether it merits new cylinders in this scenario; I'm hoping to learn more here however...

[cliffy]

Pictures are worth their weight in gold  here! :-)

[Mark942]

If this were my problem I would want to know what Savvy Aviation Maintenance service thought of this.  It's a paid service, but unlike the CYA Lycoming rep they can give advice based on experience and science.

-mark

[PT20J]

FWIW, I have always gotten straight answers from Lycoming reps and never sensed a CYA attitude. However, some of the old timers have been retiring and the newer guys don’t have as much real world experience and tend to fall back more on the published SBs and SIs. 

[Cruiser73]

2 hours ago, cliffy said:

Pictures are worth their weight in gold  here! :-)

Not sure how to photograph it well.  

My mechanic says the only way forward is new cylinders.   I feel like I am out of options.

[larryb]

I had a cylinder head separation event in my IO-360. Fortunately on the takeoff roll so no emergency. If I saw anything that made me question the structural integrity of my cylinders I would want them replaced. And I’d replace with new ones. I don’t want somebody else’s old welded and ready to fail again cylinders.

[Guest]

For what it’s worth, I’ve replaced far more IO-550N series cylinders due to cracks between the upper spark plug hole and the fuel injector hole.  This is the most common failure I’ve seen in any cylinder type or brand.

[Guest]

7 hours ago, Mark942 said:

If this were my problem I would want to know what Savvy Aviation Maintenance service thought of this.  It's a paid service, but unlike the CYA Lycoming rep they can give advice based on experience and science.

-mark

I’m guessing they would say to replaced the cracked part.

[cliffy]

For an independent assessment its well worth the cost and time to access Savvy Aviation for this situation 

I agree with PT20J in that a lot of the old timers at Lycoming are gone so that body of historical information is dwindling

Having had several conversations with Savvy over the years you can trust his judgement   He sees a lot of difficult issues every year and he's been

around a long time. In the end the cost of his service for this issue will be minimal compared to the possible repair cost. Money well spent for 

peace of mind in the decision. 

[Pinecone]

18 hours ago, M20Doc said:

Cracks between the fins that leak or flange gaskets that leak are a problem that should be addressed.  Cracked cylinders need to be welded or replaced.

Agreed.

But porosity is not a crack.  Yet.

[Pinecone]

18 hours ago, PT20J said:

I've never heard of pinhole porosity (but I haven't heard of many things ). It's hard to imagine what would cause a solid aluminum casting to become porous. What does happen is that heads can develop cracks, and the cracks are usually evident between the fins. Lycoming did have a bad batch of cylinder heads 2013-2015.

https://cessnaowner.org/faa-issues-bulletin-related-to-certain-lycoming-engines/

Skip

I know the Honda CBX 6-cylinder motorcycle back in the the 70s had an issue with porosity between cylinders.   The cylinders were very close together and the casting was quite intricate.