Walt

Walt

Well Known Member
This is what happens when you don't keep an eye on things. It started with a broken exhaust hanger who knows how long ago (which I neglected to get a pic of) and then progressed to a cracked flange. This one was likely only hours away from a compelete seperation :eek:

This aircraft has approximately 275 hrs on it!

The Tell tale signs...
IMG_6728a.jpg


A little closer view
IMG_6731a.jpg


Then around the backside....
IMG_6738a.jpg


The crack is approximately 75% of the circumference of the flange, most of it was around the back side not really visible unless you inspect with a mirror.

Moral of story, pull both cowls every oil change and use the opportunity to do a thorough visual inspection with flashlight and mirror. When checking the exhaust system be sure you give it a good tug to check the integrity of the supports.
 
Another good catch Walt. I would also have a bit of concern over the crack developing exactly along the weld line, not just in the vicinity but exactly following it.
Perhaps Larry or Russ could chime in on that observation.
 
Hey Walt, do the welds going down the pipe (from the flange) indicate that they've cracked before? I'm guessing so...and wondering why that is. Could it be an indication of an engine that vibrates too much?
 
I had the same crack in the same location. We welded it once. It reoccurred but the second time I didn't notice it until I heard what sounded like a shotgun going off immediately followed by the sound of an engine with no muffler shortly followed by a significant drop in EGT on the effected pipe. The pipe completely separated at the flange.

I did not have a faulty hangar but it cracked just the same.

The last time I took it to a friend who does a little metalwork: Gene Fulton of Fulton racing engines.
http://www.fultoncompetition.com/Fulton_Competition/Home.html
Gene welded 2 support tabs between the flange and the side of the pipe. It has not cracked again.
 
rvmike said:
Had the same crack happen at 400 hrs and called vetterman. He said that if you don't keep the slip joints lubed (mouse milk ) it will crack because there is no more movement and the weld is the first to go. Gone another 400hrs and no problems
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Mike,

You hit the nail on the head!!! and... mouse milk does the trick. :)
 
lostpilot28 said:
Hey Walt, do the welds going down the pipe (from the flange) indicate that they've cracked before? I'm guessing so...and wondering why that is. Could it be an indication of an engine that vibrates too much?
Click to expand...

If you're asking about the doubler plates with the holes in them, that's the way the Vetterman pipes come brand new.
 
Look at the gap at 10 and 2 O'clock, Just guessing here but these areas would set up a stress point for vibration work hardening to begin, if the weld was even the vibration load would be spread evenly across the weld-flange...?
 
EXHAUST

What kind of exhause hangar?? Attaching the hangar to the airframe puts far more stress on the exhaust than attaching the hangar to the engine. In my opinion there should be symmetrical doublers on both sides of the pipe. This type of failure is common on many types of exhaust. Welding all around a pipe to flange sets up stresses that lead to failure.
 
LifeofReiley said:
Mike,

You hit the nail on the head!!! and... mouse milk does the trick. :)
Click to expand...

It kind of bugs me when I am suddenly informed that I was supposed to be doing something all these years, when it was not in the documentation. I live in the middle of nowhere.

If you are supposed to put mouse milk on those joints I would expect that to be in the documentation, and it wasn't in mine. I haven't had any problems with my Vetterman exhausts for the past 1,000+ hours and 10+ years, but if I am really supposed to take this action I would like some official notification.
 
From the Vetterman site:

What is the correct torque on the exhaust flange bolts?
We recommend 140 to 180 inch pounds. Anytime the exhaust is removed the internal star washers need to be replaced. The blow proof gaskets can be used again when reinstalling the system.

(Note: Old documentation from Vetterman had the wrong torque called out, something like 110-130 in/lbs, this was recently corrected to the higher torque. FYI, Lycoming spec is 200 in/lbs).

How do I keep slip joints and ball joints lubricated?
We highly recommend that every time the cowling is removed the exhaust should be inspected and Mouse Milk penetrate be applied to all slip joints and ball joints
 
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jrs14855 said:
What kind of exhause hangar?? Attaching the hangar to the airframe puts far more stress on the exhaust than attaching the hangar to the engine. In my opinion there should be symmetrical doublers on both sides of the pipe. This type of failure is common on many types of exhaust. Welding all around a pipe to flange sets up stresses that lead to failure.
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You are correct, the hanger should be attached to the engine not the engine mount. This one was installed from the sump pan to the exhaust pipe correctly but with no rubber "shock mount", so the result was the support tube broke and left the pipe fully supported by the flange alone.
 
Walt said:
From the Vetterman site:

What is the correct torque on the exhaust flange bolts?
We recommend 140 to 180 inch pounds. Anytime the exhaust is removed the internal star washers need to be replaced. The blow proof gaskets can be used again when reinstalling the system.

How do I keep slip joints and ball joints lubricated?
We highly recommend that every time the cowling is removed the exhaust should be inspected and Mouse Milk penetrate be applied to all slip joints and ball joints
Click to expand...

I will plan to do this now but it has never occurred to me that I should check the possible website of the manufacturer of every piece of equipment on my airplane every year.

I do appreciate the information.
 
'proper' maintenance

thanks for the pics; I will be more vigilant at annual, and anytime the hood is up!
Regarding mouse milk, yes i've 'used' it every oil change, but how the heck do you know it's really penetrated the ball joint?
It's nearly impossible to grab the individual pipes and produce any detectable movement...in fact, I'm not sure I want to reef on them, for the likelihood is i'll bend or crack something that has been fine for 250 hours!
 
n5lp said:
I will plan to do this now but it has never occurred to me that I should check the possible website of the manufacturer of every piece of equipment on my airplane every year.

I do appreciate the information.
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I'm totally with you. The ONLY reason I pulled out the documentation on the exhaust was because I *happened* to be looking at this thread. Lo and behold, it clearly says the torque should be between 100 and 140 inch-pounds.

So now it's different? And the only way I would know this is *by accidentally finding this out*?

I see that the Vetterman website says it should be 140 to 180 inch-pounds. So I've undertorqued the exhaust stud nuts. That's just great. Glad I found out about it *before* flying.

Look, Larry's product is very nice, and fit perfectly, but would it be too difficult to maintain a database and notify customers when CRITICAL specs like this change? What *else* don't I know about that I can only find out by randomly reading websites?

Can you tell I'm annoyed?
 
Easy guys, the torque's not that big deal & mouse milking or applying anti-seize to exhaust joints (and nuts) has kinda been standard practice forever.
 
I disagree...if it were not that big a deal, then the documentation would have said "100 to 180 inch-pounds". I torqued mine to 120, middle of the range of the original spec. That's 20 inch-pounds *below* the now specified minimum value, or 15%.

If it didn't matter, and we're just dealing with "red torque" vs. "blue torque", that's one thing. But suppose I left it at 120, and within a couple of hundred hours, I get a crack (as happened here). I'm not going to be happy when someone (the vendor) says "you should have torqued it to *at least* 140. Sucks to be you."

I know Larry wouldn't do or say that, but you get my point...this is a big, heavy, hot, essential piece of equipment which, if it fails, is a safety hazard. Proper torques should be specified, and if a change is identified, needs to be communicated to customers and users.

I'm just sayin'...this shouldn't be something that I found out because I happened to be reading VAF one night.
 
Exhaust flanges don't crack from being loose. They crack from stress, or a bad weld. That isn't a bad weld. If you get a loose flange, you'll blow a gasket and get a soot jet. Not that that's much better, but not usually as catastrophic. Unless you let it jet for too long on something critical. I actually prefer split washers there over stars even though Lyc went to stars a long time ago. I just get the feeling that split washers apply torque more even and can handle more. I don't know why they went to star washers. I suspect the higher torque was more to get better gasket sealing as opposed to keeping them from falling off.
 
aerhed said:
Exhaust flanges don't crack from being loose. They crack from stress, or a bad weld. That isn't a bad weld. If you get a loose flange, you'll blow a gasket and get a soot jet. Not that that's much better, but not usually as catastrophic. Unless you let it jet for too long on something critical. I actually prefer split washers there over stars even though Lyc went to stars a long time ago. I just get the feeling that split washers apply torque more even and can handle more. I don't know why they went to star washers. I suspect the higher torque was more to get better gasket sealing as opposed to keeping them from falling off.
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I completely agree.
 
Walt said:
You are correct, the hanger should be attached to the engine not the engine mount. This one was installed from the sump pan to the exhaust pipe correctly but with no rubber "shock mount", so the result was the support tube broke and left the pipe fully supported by the flange alone.
Click to expand...

That is not true of all exhaust systems that Vetterman sells. I spoke with Larry just last week about this and he stated that certain designs should be mounted to the engine and others mounted to the engine mount. I have the four-pipe exhaust on an IO-375, and he insisted that it should be mounted to the engine mount, not the engine.
 
If these pipes were designed and built thicker at the flange we would likely not be talking about this today. I get it, tanks don't fly. A pipe could be thicker at the flange and taper though. Stress and vibration is causing these failures. As I stated, we augmented the strength of mine and have not had a problem since. I am out of state and my girl has my camera or I would post a pic of the mod we did to mine. We (temporarily) put a socket on the flange where the nut secures the flange to the cylinder. We welded triangle shaped brackets on both sides of the socket between the flange and pipe. It is a much stronger system and has not failed since.
 
n5lp said:
I will plan to do this now but it has never occurred to me that I should check the possible website of the manufacturer of every piece of equipment on my airplane every year.

I do appreciate the information.
Click to expand...

If you are going to build and maintain your aircraft then you are responsible to have everything necessary to do the job correctly, this mean all necessary information and manuals as applicable. Even though the experimental rules give you as the builder the authorization to do that work it doesn't mean that you should. If you are not willing to do the homework required (manufacturers manuals and staying up to date on current AD's etc.) then perhaps you should let a aviation professional do it for you. No disrespect meant, but this is a serious business and aircraft maintenance is not to be taken lightly.

So I guess my point is: yes you are responsible to have the necessary data to perform the task, and in our case because there is no MM, this means doing the necessary research from manufacturers to have the latest information available on maintaining the product.

The FAA has rules that govern mechanics on how we do our job:

§ 43.13 Performance rules (general).
(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.
 
You know, the tone of this thread is really beginning to harsh my mellow here on a wonderful Thanksgiving morning.

For those NOT involved in the fray, give thanks....and remember that most people don't spontaneously post "I have 1400 trouble free hours on my Vetterman Exhaust, have never changed torque settings, never mouse-milked the joints...." Only those occasional people that have an occasional problem post about them - to get advice, or let others take a look at something that might be a developing problem - or might not.

I am fortunate to have an earlier model RV-6 to look at - I can see many, many, many improvements in the way we have all built our planes over the years. the basic design is the same, but the way RV'ers have developed new ways of doing things like firewall penetrations, or build exhaust systems - amazing. We get better with time. If you expect an experimental design to be perfect the first time out, with no room for improvement, I;d suggest that you take a step back and look at the big picture.

There are many folks that have been stuck with components that were less than optimal, then the market drove the poor designer out of the picture.

n the subject of exhausts, we STILL have multiple ways of mounting them, and varying results with different planes and people. There are a lot of variables. The best thing to come out of this thread (to me) is to "do good inspections" and look for something unusual. No, inspecting Experimental is not about strict adherence to a manual - there is no manual that covers the entire aircraft. Do the component maintenance by the book (if there is a book), yes - but make sure that you are not a slave to the book alone - because for an experimental, there isn't one. Probe for the unusual, expect to be surprised.

Now go eat some turkey guys!
 
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