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RV-8 Exhaust System Failure

drill_and_buck

Well Known Member
Patron
Today I had an inexplicable failure on my Vetterman exhaust system. Up until today I have had 460 trouble free hours. I bought this from Larry around 2007. First flight was in November 2011. At each annual condition inspection I mouse milk the slip joints and put anti-seize on the ball joints.

Today was the first flight after my annual inspection. Because I had one of my cylinders rebuilt, I set up a race track course between two local airports, and flew for 1.8 hours at 75% power religiously monitoring the EMS. There were no EMS anomalies. At one point I did catch a brief whiff of a weird smell that got my spidey senses up but it subsided and I attributed it to the mouse milk or anti-seize burning off.

When I landed I was shocked (and counted my lucky stars) to see that the aft flange at the ball joint, on the left exhaust pipe, failed and was nowhere to be found! This left 1400 degrees of hot exhaust pouring out of the pipe adjacent to the carburetor.

The first picture shows the exhaust exactly how I found it. Note my Reiff oil sump heat pad was burnt and separated from the sump. Also note the fuel line. This is also a testament to the firesleeve on the fuel line. Note the whitish color.

Needless to say the cowl is a mess. For those unfamiliar with Vetterman's exhaust the last pictures the right hand side that did not fail. It shows the two flanges that clamp the ball joint together.

I've sent a note to Clint at Vetterman asking for some guidance on how best to proceed. I'm inclined to ship the entire exhaust system back for his analysis.

Has anyone else seen or heard of a similar failure? Any ideas what would cause such a failure? I've used the rubber hose method to hang the pipes. It's not rigid.

I'll keep you posted on my progress. Check those exhaust systems!



This is what I found when I removed the cowl:

yMHLDw2KB0oCjnGnjmvRug3NjxTAiejGfMPn2-1UKhR3bnb8wu04XZgdY7El60jUXnisci-YgI-2b-XnkxWWVwdGK_2ImedW6yjfaWyLk-GRpYY4c6GlX-a9Ov_2Q2BeEQR3QvaJ2Qm97jVV8-Kcos5Z-fXQWqzmwCGrjjJx8sJ563vthtLTlF7b8IvoyPezlLdYuR_vUHkO425LUx7mlyL6wnJx-x9NsIVs5n1hE-giYbraBi0C9R4MylmRlO9YJqQ44dHXm3biPigUGGk6mjMq_k_0rSWH9KtZvvWMbGkh-HkkPxK6tEX-9g9l6bPtANxfXYwq_E2qCz7tJp946qiOgEsdddZYWET4V4-PaLFaXLZ0xegPc6JUI5SjbMDMsgpBvyCeYc6z6mS9V8vW3rt77Bx_2UNKvdaMVPo_BeDoHvLNVM6nuDHeXEYctq57ZAe34fzUOSak_FIUxUxQatQyrj3HYpGqQ2_59miN3AyHX82nQxApKxxOwY7s-WCAmuTmgTeAp_Vbs-gOooVMRxDwLs6L1TmMdlE0STqQqsYRgw6ql6lyIzquvcKFxZPJz2rvnIDOgupZG7RVT6iDEK2baonn05n7gZN_eV0WRKt4nSHIJ2FxLflArd4037_4CtxlhLuunDL7eSRt4AWXUy_Tb7bjWLsdNyIEQqR1u3Q=w800-h600-no


Cowl damage as found:
D13GRG6bFCjt-_0R_uNyw8p_ydwpFjxod0N8s3KLGRWapYeW6wIJjyQYpPNLX-_oVAo5soKGLei4G0gSYfSCNjAF4ExFQVKDvelWKvrKk04Z6MpQ_1x19xGB9GY3sq8XcUgiW00KTIUEtw4zOw9ZZXLFX4UYMuOE-Ke-2nl7aN2jOxwWl7loO6T14zHQfx-7ShpXMEW9q61bkL-vMZMhGt--QAJ0dPNuOKMOVxMuyMsYUwzsK_7pEJBUECvHdgYr5z7U-ySJtp2RqxdV4wDgwVt8v0zSrXecGHocYKRQxDiIlkJAX-DPLFtqi8C0jb0vhKkABkUyn2pWf2eMCG2KPqeG24LV2UGCWpiAArcfiYnf-UVTEIFQvozYJWnHzE3o1UGaKHU45SOo-ovvnAlgJzmQxD9fWFKWb8YCGf8jYu4o36b3mca3VcWGwR6jcn4wu7TK0yRXIYZMrc4iM6aTMhrFRYI0_Wpsn-hKZWRcAFBnNpeqhhT3zAtP2riQXJQTJCCpXbPisc881eJ6084zpfGd2axgr1ygPbU0pZm3xA-tbPPm4Q5Bw_aS47PZtyXuvpHQmAJ4B_PkzF55LVCSUJ6kGrlyWZC5G_sIFkinMwvOYF1h8kLLnmzso8_gO-vSTAMlE0KCNznkhbxGx4AfyiGanTMVxL_639W4HojJW60=w800-h600-no


Picture of flanges that connect ball joint. (white smudges is anit-seize)
f7ZE1oe9lllMEKUkSZKRolMJ47Ikm6Vo-iYiraX8k0RdVBwcifVsiJXxBi5uDiaBW6dF4kG3fLSgWqsrYuAxwH5LBDeP5vpTIsTEvTzQJIeW3e_dd9pSJl6cUo1Pc6pL2rkQWjMntMBQoPR-UWG-phFwnhieZTeQEa8I0WpJkx18H-0VRhc1uyd6YPpVq-_3DZ8WTkHmcDLHnUdETX7RuOVcY1NWA_YLu5WJpRtR46tehf3y9t_BMhwU1_c1G6O1tDekfJSUwWjogafogkzjsUZk_OcY5sbUai8tN4DG3gi42Y9HjKxXYnvaR1vgh90m0Sxf4d0XvXbGYwFzFLhTYRBitTifFfm_8-1yNL6ZRduSiKWuaVM9GA8A8Q8c9b9m8wch7e-jnf6PqB8oiXK6mqxzVGdxGU2Rqp9v6Y1grq2mjGHruANZd1pS2ds1Jboo2lpu8Jpim7lSgEJN9BD2K9oRjdWsV4IuUsOaTILo1h26uBqiPe9RZOZPOONyiQzlvltJdT6A8iwgsz_kpV3RA3XmeJAjoABLT2pYnePU_kXgfVPbbH-fi9gBah722qYy7WyLkwquZqgqgS06g7IXtZpkDbHPDelcxu5r7x5Id71XPIn-Y7CBIOJNZymEfJe7XGPDIgjia_DSgmLeA5lR0q-Y1Z2N34mufeLCmQPdVoI=w800-h600-no
 
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I don't see the third picture. Can we see a picture of the other side?
This would seem to require a failure of three nut/bolt combinations. Very unusual to get multiple failures. That is why i ask to see what is on the other side.
 
Hi Brad,
Yes, this is really a head scratcher. No distortion of the bolt holes on the remaining flange. The flange would have had to fail in order to slip over the flare. What I can't understand is what happened to the three bolts with the metal locknuts.

I reposted the picture, hope this helps.
 
Today was the first flight after my annual inspection. Because I had one of my cylinders rebuilt,

Are you *absolutely sure* that this joint was properly assembled before the flight? Was it separated during the cylinder replacement procedure for any reason? After the cylinder replacement, was *everything* in exactly the same place as before? Were there any new stresses placed on the joint by a slight difference in the geometry with the new cylinder?

Not to besmirch your practices at all, but this sounds a lot like a maintenance induced failure.
 
Can't say for sure, but the locknuts on the right side do not appear to be on with at least one thread showing above the locknuts. They should be tightened. I like two or three threads past the nut in this application
 
It looks like your rubber-hose hangers are attached to the motor mount. The other, I think better option, is to attach them to the engine case. That way, the entire engine and exhaust assembly can move as a unit without flexing anything.

When you put the support hangers on the engine mount, and the engine does its normal dog-shake on start-up and shut-down, something has to move somewhere. One might say that that is what the ball joints are for, but arguably it is better if they don't have to move.
 
Are you *absolutely sure* that this joint was properly assembled before the flight? ....... but this sounds a lot like a maintenance induced failure.

I asked myself the same question. Cause and effect or coincidence? The flange would have had to fail in order for it to slip over the flare.

Yes I am sure that the joint was properly assembled. I remove, clean and reinstall the rear exhaust pipes at each annual and sometimes in between. I use the same procedure each time. Vetterman cautions about over tightening the metal locknuts. I tighten them until my fingernail can catch a thread. I have also had several other RV builders and an A&PIA look at the firewall forward prior to the first engine start.
 
It looks like your rubber-hose hangers are attached to the motor mount. The other, I think better option, is to attach them to the engine case. That way, the entire engine and exhaust assembly can move as a unit without flexing anything.

When you put the support hangers on the engine mount, and the engine does its normal dog-shake on start-up and shut-down, something has to move somewhere. One might say that that is what the ball joints are for, but arguably it is better if they don't have to move.

I like that idea. I am thinking that is why the flange failed. Any pics of an RV-8 with hangers attached to the engine case? The original instructions I received called for the setup I installed.
 
In my application there was no good way to attach the exhaust to the engine case. Stuff in the way

Mine are connected to engine mount also, ok so far after abut 200 hours.

Also, ball joints are different, no flanges. Ball and pipe are one piece can not take apart.

Vetterman must have changed how they are made, these were made about 5 years ago. (2012)
 
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no bolts, no flanges

Mine are connected to engine mount also, ok so far after abut 200 hours.

Also, ball joints are different, no flanges. Ball and pipe are one piece can not take apart.

Vetterman must have changed how they are made, these were made about 5 years ago. (2012)
Same here. Wow Mike - you really dodged a bullet here. That could have been so much worse.
 
I asked myself the same question. Cause and effect or coincidence? The flange would have had to fail in order for it to slip over the flare.

It definitely seems so. I wonder if it had a preexisting crack or whether some subtle change in arrangement due to the cylinder work placed a new stress on it.
 
There are similar spring-and-bolt clamps on some Rotax installations. The bolt can wear against the edge of the hole in the flange. I've seen 'em cut halfway through the shank in 100 hours.
 
what type of anti-seize were you using? some types contribute to corrosion and embrittlement.

Hydrogen embrittlement is the effect of hydrogen absorption on some metals and alloys.
Sulfide stress cracking is the embrittlement caused by absorption of hydrogen sulfide.

more info. cadmium plating caused a problem here. probably why certified aircraft do not use cadmium plated bolts or nuts for this application.


there is a Van's SB for metal lock nuts
http://www.vansaircraft.com/pdf/Notifications/Notification-14-07-03.pdf

I would only use the recommended lube for these.

and recommend castle nuts with cotter pins for the bolts.

and recommend to support the exhaust from the engine to minimize flange movement.

no%20cadmium_zps8wawmi7v.png
 
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Thanks Steve,

Nice to know that there are some anti-seize applications that can cause corrosion and embrittlement! The next time I go to the hangar I'll look up the MSDS of the anti-seize I bought at Napa and let you know what I found.
 
Nice Pictures

Andy, those have got to be about the most artistic build pictures I've seen! Really nice lighting.
 
Just to confirm...

For the 5 years since completion of my 7A, I've routinely squirted a few drops of mouse milk between the flanges (as clearly shown in the Steve melton image). Just wondering if the mouse milk is getting to where it does good? I haven't had any issues but am now questioning whether I need to change my practice.

Jim Diehl 7A
Lock Haven, Pa
 
Andy, those have got to be about the most artistic build pictures I've seen! Really nice lighting.

Ha ha, must be because my day job is at GettyImages. Even in technology the Photo DNA must rub off. :)

PS, all of those pictures are simply iphone shots. They really have come a long ways as a camera.
 
Nice to know that there are some anti-seize applications that can cause corrosion and embrittlement!

Mike .... I know your engine is not a Rotax but your exhaust is a ball and socket type made from stainless so the following is likely to apply to your instillation.

The use of anti-seize compounds with copper in the formulation is not recommended for use on stainless exhaust. Guessing Loctite LB771 Nickel anti-seize would be a good choice for you too. It is rated to 1,315*C and contains no copper in the formulation.

Happy flying,
 
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I asked myself the same question. Cause and effect or coincidence? The flange would have had to fail in order for it to slip over the flare.

Yes I am sure that the joint was properly assembled. I remove, clean and reinstall the rear exhaust pipes at each annual and sometimes in between. I use the same procedure each time. Vetterman cautions about over tightening the metal locknuts. I tighten them until my fingernail can catch a thread. I have also had several other RV builders and an A&PIA look at the firewall forward prior to the first engine start.

Are metal locknuts repeatedly reusable? Could they loose their grip?
 
stainless needs stainless

Good job getting back down in one piece Mike and thanks for sharing your experience. The firesleeve on fuel lines works, I can't recommend it enough when looking over builds.

This brings back some memories from working on certified piston engine exhausts. I recall how terrible they are and how often they cracked and needed to be replaced. The Vetterman and other homebuilt cross over and such systems are miles better, they have thicker tubing instead of thin stamped sheet with many welds. No exhaust is immune from failure though.

Definitely the hardware securing that ball joint should be stainless steel; the bolts, washers and preferably castle nuts and cotter pins. That is standard on C207 and C206 exhaust muffler connections as far as I remember. Even with stainless hardware the bolts can exhibit wear on the shanks from vibration, not uncommon to have to change them as DanH said. The springs can lose their tension holding on the flanges and make everything loose as well, compare new springs to old ones and they will probably be longer.

Self locking nuts can be re-used, the criteria for replacement is when they can be threaded on/off by hand, then the locking feature is no longer working. They do lose their grip eventually. On other airframe areas they can be reused without a problem but in this application I would rather not due to the temperature cycling.

The turboprop exhausts I work on are bolted with quarter inch stainless hardware and after several hundred hours they are so crusty they sometimes snap off even after the application of penetrating oil.

Good to know about the proper anti-seize, but I thought Vetterman recommended Mouse Milk on the ball joints as well as the slip joints? Perhaps it's the newer ones without the bolted flanges?

Interested to know what the analysis reveals about the missing flange and the integrity of the rest of the system.
 
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