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:
I'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
So I have three questions for the knowledgeable people here:
1. Is it likely that I'll be able to make a durable and reasonably neat
stick weld between these two components?
2. What type of welding electrodes should I use? I have 6011, 6012 and
6013, and can probably obtain most others.
3. Is cast iron very different to mild steel to weld? Do I need to
practise welding cast iron before attempting this job?
Any suggestions would be much appreciated.