exhaust pipe mounting problem

I am making this post to see if any other RV8-A builders with completed and flying airplanes can make suggetions for a proven, working solution for my problem. I would even welcome moral support from flying 8-A builders who have the same problem and just want to commiserate with me.

For seven years my airplane has flown with a Lycoming O-360 with the usual Vetterman crossover pipes that came with the kit from Van's. The right pipe has a heat muff for my cabin heat supply, and it seems to vibrate in its own happy little environment, causing no trouble. The left exhaust pipe moves around and bounces off the curved firewall fairing, resulting in a shattered fairing. So far, the exhaust pipe ball joint appears undamaged. At first, I used the exhaust mounting hardware that came with the Vetterman kit. After two years of trying unsuccessfully to stabilize the left pipe, I talked to Mr. Vetterman, who sold me a "new, improved" set of hardware to stabilize the pipe. It works for a few hours of operation, and then the pipe starts wandering into the firewall again. I have tweaked my installation so often that I can remove top and bottom cowling in my sleep.

Does anybody have any solutions to this problem? Whenever I talk to the builder's assistance people at Van's I learn that I am the only builder with such a problem, and they have no idea how to help me. According to a "reliable source" (not at Van's) this problem is so common as to be almost guaranteed to occur in the 8-A design. The geometry of the engine mount down tubes and the framework for the nose gear mounting truss is so narrow that any direction the pipe moves, there is danger that it will hit something immovable.

This is a wonderful airplane design with just one itsy-bitsy design flaw that defies my attempts at amateur mechanical engineering.

I'll bite

First of all, welcome to VAF! Sorry for the lack of response to your well worded question, it's just that there aren't many of us 8A builders out there.

You are right that this is a problem unique to the 8A. There are two very small windows for the exhaust pipes to exit, missing the engine mount and exit ramp by about 1/2" each. That said, I have about 140 hours on my 8A and haven't had any issues. I may have some next flight, who knows? You're probably doing all of the things I am, but just have more flight time. Here's my setup:

I worked hard to get the "elbows" in my exhaust pipes inboard, Yes this reduces exit angle of the pipe further reducing the size of the exit windows, but keeping the elbows in lets the two pipes finish nearly parallel to each other, and the reduced exit angle keeps the ends of the pipes out of the airflow under the cowl. I use Vetterman's angled tips to keep the exhaust flow from pounding on the exit ramp.

I have biased the location of my pipes down so that they nearly touch the engine mount when the plane is on the ground. This provides maximum clearance to the firewall. In flight, it is apparent that air flow moves the pipes upwards towards the firewall and exit ramp. The marks on the end of my crankcase breather pipe indicate that the pipes move up about 1/2". If you start only 1/2" from the firewall, you're going to have contact.

I'm using Vetterman's standard bracing, with the pipes supported as far back as I can. The upper ends of the supports are attached to the engine sump, allowing the pipes to move with the engine. I believe attaching the supports to anything other than the engine is asking for failure or at the very least, unwanted motion. The pipes need to move with the engine. Again, I'm really using the supports to hold the pipes down, not up. The pipes very nearly touch the engine mount when the engine is not running. (I don't show any mount damage or signs of contact.) I also have the two pipes joined to each other horizontally in the typical Vetterman fashion.

Hope this helps. I'm guessing you were doing all of this already--I can't figure out why it's not working for you. Below is a photo of my configuration.

I have the standard Vans supplied Vetterman crossover pipes with turndown extensions and have not had any problem like the one describe. The clearances between my exhaust pipes and the firewall and engine mounts are close (1/2" at most), but I see no sign that the pipes are contacting anything. My installation looks very much like the picture in Guy's post. With the 8A design, there really isn't a whole lot of room to change much.

I did have an issue with the exhaust ramp cracking, but I armored that with SS and have not seen any sign of further problems in the past 30 hours or so. I attributed that problem to exhaust pulsation vibration rather than the pipes physically contacting the ramp.

Good luck.

Craig Gallenbach
RV8A N184CG 92 hours

I have about 85 hours on my own RV8A and had some exhaust movement issues through that tight space.

I shortened the length of the rubber tubes used in hanging the Vetterman exhaust to remove some of the flexibility inherent in all those hoses working in concert. For me, this reduced the tendency of the pipes to wander out of the "sweet" spot.

I turned my exhaust down further than the ones in the picture posted by Guy so that they come from up higher and exits more vertically giving more wiggle room through the slot. Also in the hopes of reducing exit ramp vibration.

Have to be careful of maintaining distance from the fuel line of course...

Two tips that helped me

I too have struggled with the 8A exhaust - broken exhaust supports, cracked air ramp and cracked pipes. Two tips that have helped me are:

Anchor the exhaust supports to the engine, not to the engine mount. I think this helps to eliminate stress on the mounts since the engine moves quite a lot relative to the engine mount. This lets the pipes move in sync with the engine. I previously felt the exhaust mounts should be anchored to the engine mount to prevent the pipes from moving enough to contact the air ramp. But I covered the cracked air ramp with stainless and since making these changes I see no evidence of contact between the pipes and the ramp even though I have less than an inch clearance between them.

Keep the gap between the ends of the stainless steel tubes inside the rubber hose very small. I think Larry recommends a quarter inch or so. With a larger gap the rubber hose will tend to take on an "S" shape allowing the pipes to move too much. I believe the pipes were previously contacting the air ramp due to air loads "lifting" them rather than due to movement of the engine. Of course, once the mount has broken, the pipes easily move upward to contact the air ramp.

Larry's newer pipes also have reinforcements welded onto the pipes next to the manifold flange. I had two pipes that sheared completely an inch or so from the flange. (A startling thing in flight - I thought the engine was running extremely rough when it happened to me - but realized I had no loss in power, just noise and vibration.)

Larry also recommends lubricating the ball joints and slip joints regularly with Mouse Milk. I believe he says that failing to do so will almost guarantee a cracked pipe. I plan to remove the pipes completely and clean the joints on each condition inspection since I discovered that it is really pretty easy to do so. And every time I have the lower cowling off I brush Mouse Milk on to every pipe joint.

Many thanks to Guy, Craig, Claudio and Jim. I will take your suggestions and do a re-design of my mounting hardware. Those were some very good ideas, and I'm glad they have worked for you. I appreciate your help.

Now if I can just figure out a way to get the mama mice to hold still long enough for me to milk them! (just kidding)

Rich

Same problem with my -6. The RH tailpipe wants to move up in flight and will turn the support hose into an S-shape and eventually the pipe hits the underside of the fuselage. I fixed it by filling the gap between the upper and lower support tubes with another piece of steel tubing which creates a solid "block", so that the tailpipe cannot move up. Also helps to use Aeroquip 303 or some other relatively stiff hose instead of the floppy low-pressure automotive fuel hose that Larry supplies.

I first tried using a piece of wooden dowel as the spacer between the support tubes but the ends of the dowel eroded away pretty quickly when in contact with the small area that the steel tube ends provide. Then I tried aluminum tubing which lasted a bit longer than the wood, but the final fix was steel tubing.

Heinrich Gerhardt
RV-6, flying

Old thread, but I'm still having this same exact issue. The exhaust on my 8A rides too low on one side and chews into the engine mount and on the other side rides up and bangs into the fuselage. I've looked at, and adjusted, all of the items suggested here several times. I'm using fuel injector tubing, only have a very small gap between my stainless exhaust hanger pieces, and have the cross support between the exhaust pipes. On the side that hangs too low I've cut some length off the exhaust hangers in an attempt to raise the exhaust pipe, I think due to the cross support (which i did not adjust) that primarily seemed to pull the opposite side exhaust pipe in towards the middle.

I've tried to get in contact with Clint at Vetterman's to no avail, voicemail seems to be full and I can't get through. My exhaust is an older style, circa 2001, so at this point I'd gladly purchase a new one if that solved the issue.

Does anyone have any other suggestions on how to correct this problem?

FWIW, Vetterman recommends lubricating all slip and ball joints with Mouse Milk. I do this every time my cowlings is removed.