Modifying exhaust- material source question

[trib]

I purchased a used SS exhaust which was supposed to fit a 6A (originally from Aircraft Spruce). It just bumps up against the engine mount where the rear tube (2 into 1, number 3 and 4 cylinders) passes through the engine mount. The mount interference is the portion for the front landing gear. My guess is it really only fit a 6, not the A version. The fix seems pretty simple. cut the pipe, weld in an extenstion and make a small bend. Does anyone know of a source for the SS exhaust pipe? The sizes used are 1.75" OD and 1.84" OD, looks to be about .035 thick. Thanks for any help.

[Vern]

Take it to a good automotive muffler shop with a pattern for them to copy.

[gmcjetpilot]

Originally Posted by trib

I purchased a used SS exhaust which was supposed to fit a 6A (originally from Aircraft Spruce). It just bumps up against the engine mount where the rear tube (2 into 1, number 3 and 4 cylinders) passes through the engine mount. The mount interference is the portion for the front landing gear. My guess is it really only fit a 6, not the A version. The fix seems pretty simple. cut the pipe, weld in an extension and make a small bend. Does anyone know of a source for the SS exhaust pipe? The sizes used are 1.75" OD and 1.84" OD, looks to be about .035 thick. Thanks for any help.

It is either 304 or 321 SS, the 321 is what you want. 321 is better fatigue at high temp, 304 works and is used for exhaust some times but more for counter-tops. (304 is way cheaper and would be fine for a tail pipe). Here is where I get my tubes.

http://www.burnsstainless.com/

Good info on their web site about SS and welding. Remember if you get SS too hot you can create a crack maker. There is a fine line between OK and too hot. Aerospace SS welding typically uses TIG (w/ argon), some times filling the inside of the pipe with inert gas as well, to prevent brittle welds. Getting the weld too hot will make it brittle. Not all (many) run of the mill car shops know stainless. A race shop will know.

I forget the metallurgy of it, but the heat affected zone adjacent to the weld can have excessive crystalline structure change if not careful. Exposure to excess temps changes "Phases" of the metal and grain boundaries. This causes diffusion referred to as "sensitized". Also having inert gas inside the tube reduces this tendency and increase strength (back-purge). From the text book:

"The diffusion of chromium away from the grain boundaries results in un-stainless grain boundaries surrounded by stainless steel. This situation soon leads to localized corrosion and rapid cracking of the grain boundaries. To correct this, the metal must be heated to at least 1900F (1040C) for a period of time in an inert gas atmosphere and then quenched to retain the austenite crystal structure. Unfortunately, doing this heat treatment, a lot of warping and distortion may occur."

Bottom line don't use too much heat; its lower than standard ferrite steel. If some one does not understand SS welding they can make a crack monster. Read this and if your welder seems clueless of any of this, find another welder or do it yourself. http://www.burnsstainless.com/TechAr...struction.html They discuss back purging:

"back-purging with an inert gas (such as argon) provides a smooth inside weldment that is up to 30% stronger! This is referred to as back-purging because it purges, or displaces, ambient air inside the tube with a gas that does not contain oxygen. Back-purging is performed by capping both ends of the tacked-together tube and connecting an argon gas line to one end allowing a low continuous flow of gas into the tube during welding." I had to mod my pipes so I know about it. Good luck

[rv6ejguy]

Keep 321 stainless away from most muffler shops who don't have the welding equipment, filler rod or expertise to weld it properly. A volcano MIG weld using mild wire will ensure a crack on .035 321.

Needs to be TIG'd and preferably back purged for best results.

Burns has the goods at a premium price. There are some aircraft supply places which have 321 at lower prices but maybe not on low quantities like you require.

[gmcjetpilot]

Originally Posted by rv6ejguy

Keep 321 stainless away from most muffler shops who don't have the welding equipment, filler rod or expertise to weld it properly. A volcano MIG weld using mild wire will ensure a crack on .035 321.

Needs to be TIG'd and preferably back purged for best results.

Burns has the goods at a premium price. There are some aircraft supply places which have 321 at lower prices but maybe not on low quantities like you require.

Gee why didn't I say that?

[trib]

Thanks guys for the info and tips. I just needed a material source. I am not a welder, but work on nuclear submarines and have some aquaintences who are very well versed in welding SS and are willing (for a reasonable fee) to help out. I'll probably have the best looking welds in the air.