Cracked exhaust pipe - options

Chrisgoesflying

Chrisgoesflying

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Chrisgoesflying
My Cherokee is currently in annual. All looked really good until today. Cracked exhaust pipe on cylinder #1. Photo below. Question is, what’s the fastest way to fix it. Weld it? Replace it? Upgrade with power flow system?

Also, on that topic, this crack looks super clean. How could that happen? I didn’t notice anything performance wise, cabin heat didn’t turn my carbon detector black, all seemed to be working just fine and I was flying as recent as three days ago on a long x-country. I do lean aggressively which shows pretty hot egt but I only have one egt gauge so I can’t really tell what each cylinder reads.
 

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Chrisgoesflying said:
How could that happen?
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If the picture shows how you found it, my guess was it was installed under stress. As to the fix, do you want a temp quick fix or fix the underlying problem? May ask your AME his thoughts and options. Down here there are various options but I don't know how it is on your side the fence.
 
Bell206 said:
If the picture shows how you found it, my guess was it was installed under stress. As to the fix, do you want a temp quick fix or fix the underlying problem? May ask your AME his thoughts and options. Down here there are various options but I don't know how it is on your side the fence.
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That's exactly how we found it today. It looks so clean and it's completely around, fully disconnecting the two halves. Who knows how long I've been flying the plane like this. The last annual was in February (I do either annuals or 100 hour inspections and since I'm approaching 100 hours, I opted for an early annual) and this would have been caught at that time. Then, about three months ago, we did an oil change. I guess we would have noticed it if it was there already but we also didn't really look for anything so there is a chance we could have missed it then. After that oil change, I flew nearly 50 hours with no issues, with the last flight on Sunday, a 500 mile cross country and once again, didn't notice anything wrong with the plane on that flight. Should the airplane not have some sort of "symptoms" on a cracked pipe like that?

As for the fix, I just looked up the power flow system. At $5k that's a bit too much for me right now. My mechanic said we could see if it can be welded but chances are if this one cracked, it's just a matter of time for the others to crack and maybe welding won't even be an option if the material is already too fragile. Besides that, it's a new, simple exhaust system I guess unless I'm missing any other options. I'd prefer to address the underlying problem, unless that would ground the plane for more than three weeks. It has got to take us down to Florida in late November :)
 
Gary Ward said:
Sorry to see that, glad you found it. How many hours are on those pipes?
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I don't really know how many hours are on the pipes but probably a whole lot. I bought the plane less than a year ago, made sure all the ADs (especially the wing spar AD) were done but didn't pay too much attention to the exhaust system. At the same time, the engine only has 300 hours SMOH at which time it was converted to the 160 HP O320... I would assume that they installed a new exhaust system when they did the engine 10 years ago, but maybe not?
 
I like the way you think, I would also be afraid of the others cracking from age/use. I'd at least get 4 new header pipes/clamps/gaskets. See what kind of shape the muffler is.

Powerflow do work well on 0-320 and are expensive. No muffler to worry about cracking or leaking though.
I have about 900 hrs on a powerflow system on my 320, it definitely helps it climb better.

I am sure you will shop around like said above not sure how it works up north. Good luck.
 
One man’s crack is another man’s break.

are you able just to replace that one pipe? You shouldn’t have to buy a whole new exhaust and welding would be a challenge to fill that whole area. Then of course now you’ve reduced the diameter of the pipe.
That being said, the Cherokee 140 exhaust is a crap design which is why my power flow exhaust should be here the end on next month.
 
Lots of people could weld the pipes. However; alignment is another story and if incorrect could cost you a cylinder.

Frozen slip joints might cause the break.
 
Oftentimes exhaust systems will get thin as they age. This may make a field repair impractical, or short lived. A local expert should evaluate the material to decide if that sort of repair is an option.

The next fastest method of getting the aircraft back together would be to buy a new pipe. I would expect one or more aircraft exhaust suppliers should have something in stock For an airplane as common as a Cherokee.

The most time consuming option is likely going to be sending your pipe in for overhaul.

The Cherokee exhaust system should have slip joints in the pipes. I’d make sure those joints are free to allow the movement of the individual pieces to help prevent cracking.
 
Stupid question... first, I am not an A&P but I do own a machine shop. What about welding an external sleeve around the pipe? I don't claim to know anything about aircraft exhaust systems but we have repaired stuff like that in the past with a sleeve.
 
That man needs some crack spackle.
 
Joe_B1 said:
Stupid question... first, I am not an A&P but I do own a machine shop. What about welding an external sleeve around the pipe? I don't claim to know anything about aircraft exhaust systems but we have repaired stuff like that in the past with a sleeve.
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Depends on how much metal is left, how thick it is. I have welded several sets of headers over the years. Sometimes it works out and other times they crack at your weld again.
If it has slip joints then that could be the cause if the pipe was seized.
The powerflow system instructs you to re anti seize the pipes every 100 hours. I redo mine every other oil change. Not that hard, I can do it under an hour by myself on a 172 rolling around on a shop chair and using my knees to hold it up until I get nuts started.
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That' stainless steel, and it gets thin with hours, gets contaminated with carbon (soaking right into it), and loses its chromium as it forms chromium carbide on the outside of the pipe (the black film). It work-hardens with vibration and gets brittle. Just welding it, in any fashion, is asking for yet more trouble.

I'd bet that there are some seized slip-joints there somewhere as others have suggested. Long lengths of pipe expand and contract as their temperature changes, and aircraft exhaust systems get red-hot when at full power. A seized slip joint puts lots of stress on the pipe, in both directions, compressing a softer, red-hot pipe, and then trying to re-lengthen it as it cools. Snap, it goes, after it has formed cracks that should have been caught at inspections. It can also puts a lot of stress on the cylinder base mountings, pushing back and forth on the head.

There would have been considerable monoxide in that engine compartment. A leaky firewall could have been fatal.
 
Firewall did its job it seems. I also usually watch the CO thing like a hawk and replace it every six months. It did not change color even slightly.

Update on the exhaust system: The whole exhaust system was taken off today. All other pipes look to be in great shape except the one that cracked. The mechanic suspects that the other pipes were replaced fairly recently (probably during engine overhaul) but not the one pipe that gave up. He’ll confirm with the logbook later so hopefully I don’t have to replace the whole thing.
 
Chrisgoesflying said:
Besides that, it's a new, simple exhaust system I guess unless I'm missing any other options. I'd prefer to address the underlying problem, unless that would ground the plane for more than three weeks.
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Another option is have your entire system repaired by a certified shop. There are several good ones down here but don't know any up north. However, I don't think any shop could turn a whole system around in 3 weeks.

Perhaps buy one new exhaust stack to replace the broken one, inspect the rest of the system for serviceability, and when you get back from the trip look to have the whole system fixed. A good shop will have specific jigs and when done you'll have a new system at a reduced cost. At least that's how it used to be before todays supply issues.
 
Acorn Welding, in Edmonton, Alberta, does all these exhaust systems. I used to have them repair exhaust risers for the 172s, but they often just cracked again right next to the welds. One Acorn got PMA status, they started producing new risers, and I started buying them. I got tired of spending money to fix half-dead parts. The new ones were made of slightly heavier stuff, and the area just below the cylinder's exhaust flange was reinforced. That's where the OEM risers usually cracked.

In Canada we have an AD, covering all airplanes that use the exhaust system for cabin heat. The inspection is to find cracks or leaks that could poison the occupants. The AD calls for a visual inspection, with a low-pressure test and soaping to check suspect areas. I did the soap thing all the time, and also soaped the rest of the system while I was at it and often found other cracks.
 
I would expect that someone nearby on the ground could hear a strange cackle in your exhaust note. There's obviously been a lot of fire coming out of that crack.
 
Quick question: So, after doing some shopping (I need two pipes), I can buy the pipes new or on TAS for 1/4 of the cost of new ones. However, the ones on TAS came off of a 180 HP engine. Mine is 160 HP but it's the same part number. My mechanic said the dimensions of the last install will be different due to the 180 HP engine and unless we can move the slip joint, we won't be able to properly install it on my engine. When I called TAS they said the slip joint cannot be moved but as long as the part number is the correct one, it should fit my engine perfectly fine regardless of the last install. What are your thoughts? Obviously 1/4 the cost is very attractive.
 
Chrisgoesflying said:
When I called TAS they said the slip joint cannot be moved but as long as the part number is the correct one,
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I'd have your AME talk with them just to confirm. Can't offer much more due to the rules difference, but that is the route I've gone in the past down here. Regardless, I'd still look into the entire exhaust system in the near future. Maybe TAS can give you some incentive to bring all that work to them?
 
Bell206 said:
I'd have your AME talk with them just to confirm. Can't offer much more due to the rules difference, but that is the route I've gone in the past down here. Regardless, I'd still look into the entire exhaust system in the near future. Maybe TAS can give you some incentive to bring all that work to them?
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Not sure what else they would tell him. He told me what to ask them and the answer he was hoping for was "slip joint is movable" which wasn't the answer I got. I talked to him about replacing the entire exhaust system but it seems overkill since all the other parts, besides the pipe that cracked, appear to be almost new, probably installed during engine overhaul 200 hours ago. He said I could get an entire new system if I wanted it all to be brand new and then sell the lightly used parts to re-coupe some of the $$$ but that sounds like more hassle than what it's worth.
 
Chrisgoesflying said:
He told me what to ask them and the answer he was hoping for was "slip joint is movable" which wasn't the answer I got.
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But TAP still said it should fit. Maybe there was something lost in translation? I always preferred to talk to vendors directly than what my customers told me so there wouldn't be any mis-communication and where I could ask pertinent questions if needed. But thats my preference and I'll defer to your AME on his.
 
Chrisgoesflying said:
My mechanic said the dimensions of the last install will be different due to the 180 HP engine and unless we can move the slip joint, we won't be able to properly install it on my engine. When I called TAS they said the slip joint cannot be moved but as long as the part number is the correct one, it should fit my engine perfectly fine regardless of the last install. What are your thoughts? Obviously 1/4 the cost is very attractive.
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The dimensions are indeed going to be different. My question is, what slip joint cannot be moved and why not? If it is like the slip joints I'm imagining, I wouldn't want the pipes if the joints are seized anyway.
 
I bought my Cherokee exhaust parts from aerospace welders awi-ami.com they had it in stock, stack was a couple hundred bucks. The cost of getting someone to weld that part vs. a new one is probably a wash all things considered. That and piece of mind you won’t have a bunch of CO hanging out in the cowl just in time for cabin heater season.
 
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