Exhaust manifold modification

Christopher Tidy · 2009-07-23T19:42:56+00:00

Hi folks,I need to modify an exhaust manifold. When I say "modify", I don't mean repairing a crack, I mean changing the design of it.The manifold is on a 1947 lawnmower that I'm restoring. Perhaps "manifold" isn't the right term to use for a single-cylinder engine, but I'm sure people will understand what I mean. It's a 1 1/2" bore exhaust system. The silencer ("muffler" in America, I think) and manifold are welded together, but replacements are no longer available. The manifold consists of a cast iron 90 degree elbow (walls about 1/8" thick) which is bolted to the engine block using a flange. The other end of the elbow is butt welded to a thin-walled (probably 16 or 18 SWG) mild steel tube which is finally welded to the silencer. The rusty appearance of the weld bead suggests to me that it was not made using stainless steel or high nickel welding rods. Given the age of the machine, I imagine it was achieved by stick welding or gas welding.You can see pictures of the exhaust system here:'ve never seen an exhaust system where a cast iron manifold is welded to a mild steel pipe. But there are pictures of the system in the lawnmower's manual, so it's definitely original. There are no signs that the weld is failing, even 60 years later.As the authentic silencers are no longer available, I need to make a substitute. I have a Lister CS silencer and mild steel elbow of the correct bore. So I'm wondering if I can cut away the original mild steel pipe from the cast iron elbow and weld in a new section of mild steel pipe, probably with 1/8" thick walls to make the welding safer, between the cast iron elbow and the Lister elbow.I can stick weld round pipes reasonably neatly, provided that I can rotate the pipe so that I'm working on the top. This would be possible with the exhaust removed from the machine. I only have an AC stick welding set (oil-cooled with 50 or 80 V OCV). I don't have a furnace for pre-heating.So I have three questions for the knowledgeable people here:1....

Jul 23, 2009 45 Replies

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Larry Jaques 16 years ago

On Wed, 30 Jun 2010 02:34:29 +0000, Christopher Tidy wrote the following:

Cool. I just hope that's a bracket to the frame at the muffler bearing clamp. It wouldn't last 5 hours unsupported, I'll bet.

What are we going to do with you, Chris? You keep using 'advise' and 'advice' correctly here, against all trends to the opposite.

-- The most powerful factors in the world are clear ideas in the minds of energetic men of good will. -- J. Arthur Thomson

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Larry Jaques 16 years ago

On Wed, 30 Jun 2010 03:05:03 +0000, Christopher Tidy wrote the following:

Try paint that cures in the present or future next time, wot?

-- The most powerful factors in the world are clear ideas in the minds of energetic men of good will. -- J. Arthur Thomson

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J. D. Slocomb 16 years ago

A couple of comments. You can if needed, simply cut out a new flange from mild steel and then weld the entire exhaust from thick wall mild steel tubing. If you paint it the parts hat get too hot for the paint will turn black the first time you run the engine, regardless of whether it is "high temp" paint or not.

Cheers,

John D. Slocomb (jdslocombatgmail)

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Christopher Tidy 16 years ago

Just for interest, I tried to melt some lead-tin solder on the central pipe of the exhaust of a small Honda engine that had been working hard for about 40 minutes. It just melted, but nothing like as easily as it melts on a soldering iron. I'm guessing that means the temperature is about 250 deg. C. Hopefully with a larger and slower engine, my 220 deg. C. paint will be okay. We'll see...

Chris

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clare 16 years ago

The manifold paint from eastwood works well and STAYS ON if applied as instructed to thoroughly cleaned parts. Ceramic header paint works too, if the pipe is CLEAN and you follow the instructions. Even BarBQ paint or stove enamel is good to well over 600F.

Eutectic solder (63-37) melts at 361F. (183C)

60-40 melts between 360 and 375F(183-190C), and 50-50 melts between 365 and 420F (185-215C) Leadfree melts around 482F (250C).

Brazing melts above 800F, and I've had exhausts hot enough to melt brazed repairs oftener than I'd like to remember!!

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