What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Exhaust stack failure problem RV-8A

rv8apilotpab

I'm New Here
Fellow RVators

I have 750 Hrs on my 8a. It is certified and used for IFR flight and I need reliability.

I have Vetterman stainless exhaust and Vetterman pipe support bracket system. I have a Lycoming IO 360 angle valve. I have just had my 4th exhaust stack failure in the 750 hous I have flown on this airplane. Each time the stack breaks at the weld of the pipe to the exhaust manifold flange. 2 times on no 2 cylinder and 2 times on no 3 cylinder. 3 breaks have been on new stacks and one on a reweld by a local shop, not Larry V. One of the broken stacks was rewelded and fortified by Larry who uses a jig. It has not rebroken.

One of these failures occurred at night in winter over Lake Eirie. With typical British understatement, (she is British, I am Canadian) my wife who was with me on 2 of thes failures, stated, "I don't like it when that happens."

So, can you help me please with ideas about how to prevent a re-
occurrence.

Yours pab
 
How are you securing the ends of the exhaust and are you using Mouse Milk to lubricate the slip joints whenever you have the cowl off?
 
500hrs still okay

I have an 8A and so far not issues with cracks. I am always readjusting to keep the pipes off the weld mounts. Mine always just touch the low part.

I also add mouse milk to each joint every time I have the cowl off which seems to be 6 or so times a year. Along with this is an inspection of each pipe.

Cheers
 
Cross over arrangement? If so, which cylinders are you pairing?

If what I'm seeing from the Vetterman site is what you have, it appears that the cylinders "before" the exhaust tube are experiencing the problem.

I'll also assume you've been using mouse milk each repair (if not more often)

I'm guessing you could investigate doing something to better support the exhaust pipe closer to the ball joint???

FWIW
 
Where are the clamps anchored.

Where the clamps/supports that support the tail pipes are anchored makes all the difference. If you have them anchored to the engine mount, I think you are going to get cracks.

If you anchor the clamps to the cylinder block, I doubt you will get cracks. This allows the whole engine and exhaust system to move as a unit on the dynafocal mounts without putting any stress on the pipes.

I have 400 hrs on mine, clamped to the engine block. I do not use any mouse milk. No issues.
 
I had problems with exhaust pipe cracks on a Vetterman crossover system on an RV-8 with IO-360-A1B6. I had the #3 pipe break completely off at the flange on the way back from OSH in 2011, with about 250 hours on the system. The exhaust went back to Vetterman for repair. A year later, I found a significant crack at a Y joint, also repaired by Vetterman. In July 2013 I found a crack at the #3 flange - there wasn't enough time before OSH to get it to SD and back, so I had it repaired locally.

I discussed my issues with Larry Vetterman, and he said that the crossover system on angle valve engines on RV-8s had the worst failure rate for cracks of all the RV model/engine model/exhaust configuration combinations. He suggested that I replace it with a four pipe system, as that was the most durable configuration (with the four-into-one a close second). I had Vetterman make me up a four pipe system with thicker than normal tube for the first few inches on each cylinder. That system went on in December 2013. So far it has been trouble free (I've probably cursed myself for saying that in public though). I'm a few thousand miles from the logbook, so I'm not sure how many hours I've put on it, but it isn't a huge number yet.
 
What does that sound like?

A pipe breaking off in flight?! I am curious what that sounds like as well as other in-flight indications when the event happens? Seems like a frightening event, considering 1200+ deg exhaust leaking into the cowled area? Perhaps only a smallish gap appears, still funneling most of the exhaust thru the pipe?? More details appreciated. :)
 
Well it can sound pretty bad! I had a pipe on my #1 cylinder break very near the cylinder flange. This happened on initial climb out, probably 350 feet AGL or so.

I thought I had a major engine failure. Reduced power to idle, pitched for best glide. I then made a 180 back to the airport after I confirmed that I was still able to make power. I landed on the same runway I took off on (opposite direction). I pulled the mixture as soon as I touched down and coasted onto the taxiway. The local FBO came and towed me to the ramp.

I was very relieved when I removed the cowl and saw the #1 pipe completely broken off. It was a PITA, but the engine was all good so I was happy!

My exhaust was also Vetterman cross-over on an angle valve motor. Clint got me fixed up, but I also experienced a couple other more minor cracks in the system. I now have the four pipe system with a couple hundred hours on it and no problems. I think that not tying the cylinders together will make it more reliable. Very pleased with the four pipe!
 
Wonder if some head girdles, like those produced by Skydynamics would help
solve the cracking problem on the angle valve motors ??

I'm considering turning something similar out on my cnc mill for my parallel valve O-360.
 
A pipe breaking off in flight?! ...... More details appreciated. :)

During GNAR III, I sheared off #2 pipe at the flange while at full power race speed and <200agl. Scared the **** out of me, I didn't know what when wrong at first. The power pulses were loud and was torquing the engine over enough I could see the engine hitting the cowl. Almost thought I lost a piece of the prop or something, maybe a piston and cylinder had come apart. pulled power and pulled up to best glide, called ABORT on the race channel. Seemed smoother at 1800 but popping loudly.
As I turned inward on the course(towards the finish airport 20miles away, Bob B was behind me and said don't go across there, its no mans land all lava rock and scrub brush. I was looking for a landing place certain that my engine was not going to be running much longer. 15seconds in the engine is still running, still have oil pressure but EGT was under 100 and CHT was falling fast. I was holding 1400agl and 100kts paralleling a highway. Bob flew under me looking for smoke or oil streaming...nothing. 14nm to Waterville took for ever.
yeah it gets your attention and was so happy it was only a failed exhaust. Got a local welder to tack it together then we removed it and took it to his shop where they welded it up nicely. Flew it home later that evening 300+miles.
To be fair I had been experimenting with a different exhaust hanger arrangement to minimize drag in the cowl outlet.
 
A pipe breaking off in flight?! I am curious what that sounds like as well as other in-flight indications when the event happens? :)

In my case it sounded like a shotgun going off immediately followed by the sound of an engine with mo muffler.

Mine cracked at the flange a couple times. We welded it a couple times. Finally this mod worked to prevent recurrent cracking (welded tabs are just wide enough to fit a socket):
http://lancairtalk.net/download/file.php?id=5248&mode=view
 
There are many, many angle valve 8's flying.

Is anyone else having pipe failures like reported here?

Yes, pipe failure is serious and noisy. If you don't have a fire you are lucky.

Been there done that but not with an RV.
 
Last edited:
My 10:1 angle valve -8 has not had any exhaust issues using Vetermans, but with the little wheel at the proper end my exhaust doesn't have to do the acrobatics yours does in order to find its way out the back. I would read every response you get here and consider them...then call Larry Vetterman and do whatever he says.
 
Picture isn't viewable by non-members!

1zpoew9.jpg
 
Oooooh, I would have been tempted to put a "peak" or a curve in the portion that attaches to the tube.

Left circular, it approximates a stress concentration.

That being said, it may be so good that my point is unmerited, but the thought about distributing stresses carries across the spectrum of tasks we conduct to build an airplane.

FWIW
 
Washers

I notice in the photo posted of the welded flange gussets that the stud nut has 2 washers...a standard flat washer and then a star washer under the head of the nut. I had a discussion this last week with Vettermans about the correct torque for that nut. Many years ago they called for 100-140 inch lbs...then they changed that to 140-180 inch lbs...now they say 180 inch lbs.

However in providing the figure of 180 inch lbs Vettermans also recommended that the flat washer be deleted...that only the star washer be used. They claim that systems with both washers have proven to have a higher tendency to come loose. That surprised me but I suspect they speak from experience.

This is not directly related to the OP but it may be of interest.
 
Exhaust

RV-4 with a parallel valve IO-360, 4 into 2 crossover exhaust. Kept breaking the little mounting tabs, rewelding, breaking again. Finally called Vetterman to discuss and switched to a 4 pipe exhaust. Made a new stainless exhaust bracket along the back to hold all 4 pipes together on the back of the engine case and angled to clear the lower cowl. Several hundred hours now and completely trouble free. Sounds to me like the crossover 4 into 2 may be introducing too much vibration/ stress potential IMHO.
 
Post #16

Marc is correct, that is very poor design and not in line with standard aircraft welding practices.
Some factory aircraft have similar doublers however the upper portion fits immediately over the flange weld and tapers at the bottom at a thirty degree angle on both sides. The sharp point can be eliminated by making a very narrow flat at the end- 1/4 to 38" wide.
Another style doubler has the edges bent down to join the pipe and is welded all around.
 
Washers

Lock washers only on my Pitts for 1000 hours. One small crack at flange weld, no other problems.
 
Exhaust

My 0 320 powered non RV is sitting 600 miles form home. Exhaust support to bolt in sump/accessory case. Bolt into accessory case failed at base of threads. Engine is coming off, then sump and accessory case. Accessory case will go to Divco to see if they can get the broken bolt out.
So there are perils in the case mounted exhaust supports. Best to give a lot of thought to stresses on the bolts into the case. In my situation I should have used a flex link at both ends of the support tube. On my Pitts I used a short piece of #8 aeroquip hose as a link on the lower end, that works ok also.
 
Exhaust Failure

Having survived a couple of major exhaust failures on turbocharged twin engine aircraft as well as a couple in single engine non turbo, I treat the exhaust system as I would a loaded gun in my mouth with my finger on the trigger.
The ONLY safe bet is to shut the engine off and put the airplane on the ground IMMEDIATELY. Trying to reach the nearest airport could very well kill you. The only thing worse than an exhaust failure is a massive fuel leak.
 
I have a 4 to 1 exhaust from AWI (Aerospace Welding) which has ball joints on each cylinder. I have used them in my repair facility for years and have found them to be great to work with and they turn out a really good product. When it was time to put a system on my 8 I went to them and have been very pleased with the product. No cracks, and it sounds and looks great!
 
Back
Top