Metal-forming question

[Smitty]

(Oh man, I hope I haven't asked this before, and had it fall right out of my unicellular brain . . . !!!)

Somewhere along in the mid-to-late Seventies, IIRC, Konig made a change in the 2-into-1 headers he put on the fours (maybe twins as well, but the engine I saw was at Yelm, a B belonging to Dan Kirts). Before then, these headers were simply made from ordinary exhaust tubing of a constant diameter. But on this engine of Kirts', the part of the header right after the 2/1 merge was tapered . . . all except about the last 1/2" to 3/4" (as it appeared to me). This last little bit was of course sized to be a close sliding fit to the straight sliding section of the expansion chamber. All of this was like the older slider pipes with the exception of that tapered header pipe.

How did Dieter form this tapered section? Or maybe I should ask, how do you do it in a home shop? I can guess at how it might be done (by slitting a piece of straight tubing with a skunk wheel to make a very narrow pie-shaped cut-out, and then progressively welding from the apex of the cut while working the edges together). But I'd like to know how you ace metalmen do it.

[dwhitford]

How did Dieter form this tapered section? Or maybe I should ask, how do you do it in a home shop? I can guess at how it might be done (by slitting a piece of straight tubing with a skunk wheel to make a very narrow pie-shaped cut-out, and then progressively welding from the apex of the cut while working the edges together). But I'd like to know how you ace metalmen do it.


That's how I do it, Smitty.

[fcliff]

For the mod system I use a properly sized mandrel and press it into the stub.

[Steve77t]

Konig had a solid piece of steel that had the taper. It was then pressed into the tubing. This is how I do it, fast and simple, Steve

[Smitty]

It's a two-piece tool, right? A tapered piece to drive into a block with a tapered hole? Do you heat up the tubing first, at all?

When I did a few pipes, way back, I'd buy exhaust pipe U-bends from J.C. Whitney (whenever they had one of their frequent sales). In their catalog (their PRINT catalog!!) they had a table that covered the range of tubing diameters and the range of bend radii of the U-bends. The diameters went up by 1/8" increments; 1 1/2", 1 5/8", 1 3/4", 1 7/8", and so on. Using tubing sections that were, nominally, 1/8" apart gave you a nice sliding fit for slider-pipes.

Now, if I were to take a shot at making one of these tapered headers, my inclination would be to use inner and outer tubes that are 1/4" different to start, and machine my two-piece press-tool to swedge the inner tube-section out by that amount. But that's not much taper, only 1/8" over what, like five inches? How far can you stretch the diameter of this m.s. tubing before you split it or weaken it too much?

BTW, where do you get m.s. exhaust tube now? Looking at Whitney's website, they still carry it, but like a whole lot of commercial websites, Whitney's is almost unusable, at least by an old guy like me. I can't find a table of sizes, only full pages selling ONE size of U-bend, with ONE bend radius. Completely user-UNfriendly!! Gawd, do I miss print catalogs!!!

[fcliff]

It is a single piece. A plug that is shorter than the piece of tubing you are stretching. It needs to be shorter in order to press it back out when finished. This can be done cold. Enlarging the taper by 1/4 diameter is as much as you want to do an is really more than it sounds.

[Smitty]

But the header pipe I saw had the last 3/4" or so straight, not tapered, and that short straight section was sized to be the inside part of the slider part of the pipe. How can you do that with a one-piece tool? I can think of ways this might be done, but you must already have worked out the best way.

Stretching the tube an additional 25% of diameter is pretty impressive to me, but then I haven't tried this yet. Where the bottom of the tubing stands on the platform of your press, does some of that edge get distorted to where you have to cut it off, or is the whole thing still useable?

[Rex Hall]

The last 3/4 inch is turned straight in a lathe. You use a tapered mandrel to keep the header tube straight while you turn it to the dimension you want.

[fcliff]

Remember the tapered mandrel is shorter than the tube you are expanding. When it is pushed into the tube you push it beyond the the edge so it quits expanding creating the flat you are talking about. The shorter mandrel lets you push it back out and creates the flat spot. Try is you will see what I mean.

[Smitty]

Okay, now I see it, Cliff. And Rex, if you are talking about doing something sort of like the lathe practice called metal-spinning, I can see that too (I've never had a project that gave me reason to try metal-spinning, though it looks interesting). Rex, you see all the latest tricks out of Italy; are they using the sort of tapered header-plus-slider-pipe that I tried to describe here?

Thanks to all for educating me. Here's wishing you and yours a fine Thanksgiving.