Building/Modifying Exhaust Systems

[MontanaMike]

I sure would not hesitate paying Vans/Larry Vetterman for a new exhaust system for my conical O-320 RV6 project when the time comes, but I wonder if anyone had had the experience of modifying a conical O-320 RV4 Vetterman into a conical 6 system by cutting and welding? I would appreciate any input, no matter how brutal. My "education and enjoyment" might be enhanced by such an activity, and recycling seems kind of trendy, doesn't it?.

MontanaMike
RV-6 20716
Canopy/Panel/ADI P2

[Rick of Austin]

Mike,
I did something very similar and modified an exsiting one for my -6. At the time I was on a budget so when I discovered that a new exhaust system was just about as much $$ as a TIG welder so I bought a welder (Syncrowave 180 SD) and was very happy with the way the exhaust came out.
As it turns out welding stainless was much much easier than the 4130 I had been practicing on.
Best of luck.
Rick

[gmcjetpilot]

No welding expert but its OH SO EASY to make bad stainless steel welds if you don't know what you are doing. Even people who make RV exhaust systems for a living have cracks sometimes, it ain't easy. Allen Tolle made pipes long ago; super nice guy grand daddy of RV builders but his pipes cracked a lot. So what he did was not goodness. Some say just weld it. OK.

The aerospace quality welders fill the inside of the pipe with inert gas and temp control is critical. The cracks happen in the heat effected zone next to the weld. Stress relieving (carefully controlled) is another thing true high quality aerospace stainless welds get on critical items. I'd consider exhaust leaks and cracks critical.

Just Google the topic of welding stainless steel. If you are doing a counter top its no big deal, but when you are talking pipes under thermal and vibration fatigue its a different game.

Could you do it? Yep if you are careful. The separate pipes are not under the same stress as the other set ups like a cross over. I have also seen some terrible welds last a long time. Welder Karma?

If it cracks you cut out the section and weld in new pipe until you get it right. Pretty soon you will be the SS welding expert at the airport. You can always hire someone, but if they don't know stainless they may cause you to have a crack making machine.

[frankh]

But my friend makes his exhaust systems from mild steel...I.e buys all the premade bends from the ocal muffler shop.

Claims he has about $35 in his exh system..He tack welds them with a wire feed, then removes and gas welds the whole thing allowing for slip joints etc.

Claims he does not get cracks (cus mild is more malleable) and they last several years..

When they are toast I guess you just make a new one.

Now I would never had thought of this, but now I seen what he can do I think I might do the same if ever my Vettermen cracks beyond repair.

The flanges are simply 1/4 steel plate and you cut the holes out.

Frank

[airguy]

I have made my own mild-steel exhaust systems for large air compressor units in road-towable trailers for years. My oldest system has over 3000 hours of engine time on it plus over 100,000 miles of non-running tow time, and has no leaks and has needed only one clamp replaced for repair.

One word - EXPERIMENTAL - do what feels right if you have confidence in it.

[N162RV]

My cousin ran a muffler shop for year so I had him fab up an aluminized mild steel system for my -6A. After 260hrs have had no problems other than hanger brackets cracking which I have since remedied. The system only weights 2-3 lb more than the SS system and cost alot less. Tony Bengilis would be proud!

[gmcjetpilot]

Originally Posted by frankh

But my friend makes his exhaust systemsFrank

Yep that is a good one. There is nothing wrong with mild steel, cheaper (by a factor of 7?) and easier to work with. It will rust and probably not last as long. Its not going to go 20 year, but the cost is much less. If you want to experiment and make pipes, cut them, modify them you could do it in mild steel. When you get it right you can send it out to someone like Aircraft Exhaust Technologies and they will make a stainless steel copy.

[osxuser]

Yep. There are a few companies out there that make some nice exhaust systems custom. I used Custom Aircraft Parts in El Cajon, CA. They are a bit pricy, but I sent them an old, broken, Incomplete mild steel system off a W-8 tailwind and it came back as a beautiful SS system that fit almost perfectly, even with the bad description and pattern they had to work with.

[MontanaMike]

Thanks to all of you. I expected "You'll shoot your eye out", but it was very encouraging. I will report on how this works out, or not.

OSXUSER: ah POC, took primary w/ Runway 3-7- Wayne Gore...don't think they are still there. Good memories of SoCal.

[Mel]

Actually mild steel works quite well for RV exhaust. I had one of Vetterman's first mild steel systems on my -6. I flew it for 3 years and a little over 300 hrs. I sold it to another RV builder and as far as I know it's still going. Since there are no places in an RV exhaust system to trap water, they really don't rust out.