#441
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Now that I have motor mounts in place, it is possible to roll the chassis outside for that overall type picture. I'll try to get that done before the engine gets pulled again (hopefully in the next few weeks) and post up the pics.
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Joel Heinke Be original; don't be afraid of being bold! |
#442
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Header Fabrication in 304SS
After completing the header mockups, I had all the information needed to order up all the necessary U bends, double slip collector, Y pipe, V band clamps, and collector tabs in 304 stainless steel to fabricate the headers. It was all delivered in one big box (packing materials removed before picture).
The double slip collector does look like it will seal much better than the single slip variant. I decided to fabricate the aft/passenger side header first since the engine was currently sitting in the chassis and this header needs the engine, transaxle, and chassis all in place to ensure clearance around all these items. The first step for this header was to port out the flange as the primary tubes connect to it at an angle. The flange was port matched to the head and then blended to ovals on the outboard side as the primary tubes connect to it at a 50 degree angle. Next I had to turn up some special tooling on the lathe for stretching the ends on the mandrel U bends for proper fit up. A mandrel bender shrinks the tube a bit and distorts it out of round while making the U bends. I had to make three tapered stretching dies as the primary tubes are composed of three different sizes of tube. I put my metal shaping skills and tools to good use in resizing tube ends to get a perfect match. A big ass hammer and sandbag were used to drive in the tapered dies and then a combination of body hammer and half round slapper were used to stretch out the metal. All of the metal stretching needs to be done on the inside of the curve as that is where the metal is thickest. After the mandrel bender finishes its thing, the metal on the outside of the curve is only about half the thickness as the metal on the curve inside. I also used a bench vise with rubber jaw protectors to persuade the out of round openings back into round. I decided it would be much easier to fabricate, install, and remove this header as four separate primary tubes versus a single integrated unit so the flange was cut into four separate pieces. Then it was pretty much following the mockup header as a pattern to route the primary tubes. The primary tubes go to the next larger size tube every 9 ½” so from 1 5/8” to 1 ¾” to 1 7/8”. This gives the effect of a gradually tapered primary tube which makes for better exhaust flow. The one new wrinkle not experienced when fabricating the mockups is that 304SS is not magnetic. I had made use of strong magnets to hold tube sections together for welding when I did the mockup headers. A tip I had been given was to use a special worm drive clamp to position tube sections that are stainless steel. These clamps are made for very large hose, are composed of the worm drive and extension sections where the extension section has small “windows” in it for connecting to the worm drive section. With a very steady hand on the TIG torch, you can make tack welds through the window. These clamps worked well where two fairly straight sections are to be joined but not so good for joints on curved sections as it was hard to keep the joints tight when the clamp was tighten. I found aluminum foil tape to work best when joining curved sections. The joint could be positioned and then held with 2 or 3 small pieces of tape. The joint fitting could even be fine tuned after it was held with tape because the foil tape is semi-rigid. The aluminum foil tape tolerates a decent amount of heat so it’s good for use during tack welding. Well after a few days work, I’ve transformed a bunch of U bends into half a header and tack welded it up. Hopefully now that I’ve got the tooling and process figured out, the progress will go faster.
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Joel Heinke Be original; don't be afraid of being bold! |
#443
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Look good Joel!
Thanks for sharing. Steve
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Steve Hamilton Hamilton Classics Auto Restoration & Metalshaping |
#444
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Be ready for how much stainless moves when you fully weld it. Way more than mild steel.
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Marcus aka. Gojeep Victoria, Australia http://willyshotrod.com Invention is a combination of brains and materials. The more brains you use, the less materials you need. |
#445
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very hard to know where yours will move to when hot, hope it work well! Steve
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Steve Hamilton Hamilton Classics Auto Restoration & Metalshaping |
#446
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I am dressing each tube section end dead flat so there are no gaps in the weld zones there. I plan to weld at 30 amps DC with full argon purge within the tubes during welding. I plan to TIG braze the flanges on with silicon bronze to minimize warping in the flanges. Are there other things that can be done to avoid warpage in the primary tubes? I guess I could TIG braze the slip joints where the tubing size changes instead of welding them. I think the butt joints need to be welded for strength and to avoid cracking. I appreciate any helpful tips from you guys with SS welding experience.
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Joel Heinke Be original; don't be afraid of being bold! |
#447
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Joel Heinke Be original; don't be afraid of being bold! |
#448
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Header Fabrication in 304SS (cont.)
I was warned that when SS mandrel bent tubes are welded they would warp/move often in seemingly random ways. This is even when the joints are tight and held with 4 good tack welds. I’m sure the movement isn’t random but given this is the first set of headers I’ve fabricated, I was sure I couldn’t accurately predict where they would go. So I decided to weld up the butt joints first and reserve the slip joints for making adjustments if needed. With the butt joints welded on 3 primary tubes here’s what resulted.
These all started with 5/16” gap between them and the ends even with each other. I could easily slip the collector on and off of them. Needless to say, the collector won’t go on these as they are without some serious persuasion. So I’ll grind off the tack welds where needed on slip joints, make adjustments, and then complete the welding on them. Hopefully the slip joints will have less movement when being welded. I’m told the underlying cause of the warping is the different metal thickness resulting from mandrel bending and thus the welding induced shrink rate varies on different sides of the tube. The other tip I received was to make full welds on the joints closest to the engine before tack welding joints further down the primary so that adjustments can be made along the way thus eliminating the need to break tack welds. I’m going to try that approach on the 4th primary tube to see if it goes better. It’s all good, this whole Miura project is a big learning experience.
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Joel Heinke Be original; don't be afraid of being bold! |
#449
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That's how I built mine. Weld one joint at a time, then dress/tune up each successive joint on the belt sander as needed and weld the next....etc. Best, Kelly
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Kelly Coffield www.inlinecarb.com - My Old Carburetor Habit http://www.alloyavenue.com/vb/showth...nace-Build-Log - My Home Foundry Furnace Build |
#450
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Header Fabrication in 304SS (cont.)
For the aft header, it was time to complete the full welds on the primary tubes. I ground out the tack welds on the slip joints to make adjustments for the warping from the initial welding. The welding schedule I chose to use is: weld butt joints starting closest to the engine working in sequence down the primary tube while skipping the slip joints, refit the primary tubes on engine/chassis; mark, tack and then weld the slip joints starting closest to engine and working down the primary tube.
Here’s the result where the primary tubes meet the collector. The collector now easily slips onto the primary tubes after all joints are fully welded. I now need to weld on the double slips and collector tabs to complete this header.
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Joel Heinke Be original; don't be afraid of being bold! |
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