Exhaust manifold modification

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:

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
pre-heating.
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.
Many thanks,
Chris Tidy

If you were simply attempting to repair the mower, it might be worth a try. But you say you are "restoring" the mower. I would recommend preparing all the pieces, and spend a few bucks to have it all professionally welded.

... probably a true artist out there that can do it. For mere mortals such as myself, I wouldn't try it. I looked at your pics. Can't you cut just above the muffler and use a swedged and slotted tube to clamp the new muffler on? Just like all other mufflers are done now days. may need a muffler shop to custom make up this.
Karl

I vote for Karl's suggestion, since your original post says you are not trying to "restore" the unit. You may also be able to find some suitable tubing to make a sleeve to go over both tubes at the joint, eliminating the swedging operation.
Exactly where is the problem with the existing exhaust system?
Paul

Since it is a restoration, I would be more inclined to open up the old muffler, which appears fairly large and build another muffler inside the old tube.

I had wondered about this myself. Of course, there's a somewhat vague dividing line between steel and iron. But the elbow is definitely a sand casting.
I was intending to use thicker-walled tube, about 1/8" thick, to make it easier to stick weld. My welder isn't really what you'd call a buzz box. It's an oil-cooled machine which gives a pretty stable arc and a higher OCV.
Using the thicker tube, does it sound possible?
Chris

You will find that cast iron or semi steel and stick welding is a RPITA. Thin cast iron that has been repeatedly heated and cooled changes grain structure: EXTREMELY BRITTLE. This also makes it very hard to weld and then cool without cracks.
Choice 1 would be to cut the tube at the side of the muffler (silencer), find another muffler with suitable side entry, use clamps to fit it up.
Choice 2 is to find some stock elbows at the auto parts suppliers and figure out some way to get from here to there. You are looking for parts that look like this: From a place like this: These guys are fairly spendy, these items are available from race car suppliers. As an alternative, you can dig through the collection of pre bent auto exhaust pipes at your muffler replacement place, should be able to find what you need.
Choice 3 is to make the manifold from scratch. The flange is cut and drilled from 1/4" (6 mm or 8 mm) stock. Slide the tube through the flange and weld it from the ENGINE side, grind it smooth.
PS: I still owe you some parts!!
Christ> Hi folks,

There's some confusion here. When I said "restore", I meant "restore to good working order" as opposed to "restore to as new condition". I'm prepared to compromise and fit an unoriginal silencer, especially as funds for this project are limited.
I looked for another silencer that could be fitted with a clamp. Silencers with an entry tube in the side are uncommon. I could find a shorter silencer with an entry tube in the end, but then I'd have to get someone to fabricate some custom bends, and that was getting too expensive.
The bottom of the silencer is full of rust holes, presumably where water collected. Two of the internal baffle plates are rusted through too.
The weld on the original exhaust elbow looks just like a stick weld, which is why I'm thinking along these lines. By the way, I should mention that I have a spare cast elbow, so if I try this and screw it up, it's not a disaster. So I'm wondering if there's any chance this can be stick welded, and if so what electrodes I should use?
Chris

I don't know if brazing is appropriate for the working temperature, but if so, I would try some nasty old cadmium laced brazing rod.
I would think metal in an old exhaust port would be so deeply contaminated with heavy organic contaminants as to be very hard to weld cleanly.

Ok. In the past, I have used flexible electrical conduit at the end of a tractor exhaust pipe to go into a gopher hole in attempt to "smoke im out". Didn't leak much. Do you have any access to such a flexible tube? Could be brazed or clamped at both ends just to get you going.
Many years ago, flexible exhaust pipes were available at auto parts stores. Also corregated bendable tubing. Perhaps the sizes would be too big.
Another viable option is to use soft copper piping. Slit the ends for clamping. Easily hand bent to sit your project.
Paul

I think your best bet would be continuing your search for a side inlet muffler.
I don't think stick welding is going to provide good results. Even 1/8" steel pipe is pretty thin for an AC welder.
You do have a lot of space for locating a new exhaust. If a side inlet proves impossible to find, you might shorten up your header and mount something vertically.

I would except that I don't have a torch big enough to bring the joint up to a nice bright red heat. I'd also be a bit concerned about the strength of a brazed butt joint.
Another possibility is to turn a mild steel collar which goes over the original pipe at one end and the Lister exhaust elbow at the other, then weld the collar in place. This was my original plan, until I found that no one sells tube of the right dimensions. So I'd have to bore out a 2" solid steel bar on a Myford, which I'm not keen to do.
Chris

-snip-
what a neat old lawnmower. funny and goofy too from an u.s. american point of view. your project reminded me so much of what i did to my 1970's Troy-Bilt Horse rototiller i wanted to take some pics and show ya.
i did what another poster suggested, made a flange (had a piece of 3/4" steel, figured it would be better than 1/4") with the hole (hole saw) slightly larger than the pipe that was to go in, flared the pipe a little and welded the pipe to the inside face of the flange. the cylinder is an old propane tank. i can't remember but i think i might have run the pipes around past each other on the inside of the cylinder in an effort to break up the sound/noise. i ran the exhaust down and forward hoping that would also attenuate the noise. original muffler was what i considered to be a frustratingly cheap stamped sheet metal muffler, seems to me they rusted out in only a couple years and the baffle that's inside them rusts out even sooner, then you've got a enormously loud straight pipe directed practically right at you. i was tired of getting (occasionally, under the right conditions) exhaust fumes right in my face and didn't want to spend money on another piece of junk factory made one so i did this thing. i secured the down pipe to the engine so it wouldn't be hanging off the pipe at the engine flange, figured vibration would break it off. i didn't do any calculations at all and so have no idea if this thing is actually damaging or reducing performance of the engine, only just had a propane tank and thought "THAT looks like it would work!" it's been on now for several years and so far still seems to be doing ok. much relieved at the reduction in noise (kinda sounds like "huff puff chuff" now instead of "BANGBAMBOOM"). was quite proud of it when i finished.
good luck w/ your project.
b.w.

Hi Bill,
Thanks for the picture. I like that look of that tiller. It looks a little later in design than my lawnmower, but similarly solid. What's the displacement of the engine? The one on my machine is 596 cc. I've actually been offered another of these big mowers, a different make from 1962. I think it's going to be hard to resist.
Like you, I figure that the exhaust needs more support than just the flange (I think I can see another support low down in your picture). That's why I want my exhaust to go downwards. The good thing is, if I try welding the casting and screw it up, I can always fabricate a flange like you did.
Best wishes,
Chris

Please excuse this quick post as I have only scanned the current crop of cast iron welding threads and do not want to directly address any specific replies, but there are a couple of simple points that I think need to be made. All the following is just IMHO.
1) The exhaust system was welded during manufacture which seems to indicate that it can be welded during repair.
2) The photo is not enough of a close up for me to tell accurately but it seems to be a plain long radius pressure piping elbow which should be available at any quality industrial plumbing supply. These elbows are designed to be welded and usually come pre-bevelled. The long radius elbows are less common and more expensive than the short radius elbows. Both are also available as 45s and often as 22 1/2s but the 90s can be cut to any angle. They are not really expensive and are really handy for truck grill guards and handrails (1 1/4"). They are much cheaper and easier and faster to use than a pipe bender.
3)Fixation on welding cast iron is most common amongst the most inexperienced welders. Most of what people think is cast iron is really cast or forged steel. The easiest way to tell is to try to cut it with an OA cutting torch, if it cuts its steel, if it just melts and blows away then it is probably cast iron. This is much easier and a better indicator than a grinding spark test.
4) 6010 (6011 on AC not nearly as nice as DCRP) is IMHO the only real way to get a full penetration weld on pipe but without root grapes inside which can reduce or obstruct flow. Really good guys can sometimes do roots with 7018 DCSP on larger pipe, but few bother to try. I have never found a use for 6012. 6013 is handy for many special uses but IMHO is not a very good GP rod. 7018 is by far the best GP rod.
5) Small pipe is harder to stick weld than big pipe, IMHO pipe smaller than ~1 1/2 or 2" is easier to weld with OA (or TIG), I like uncoated HT rod but I do remove the oxide with sandpaper before use. OA gas welding uses the same rod manipulation technique as TIG, and is great TIG practice
6) I seldom use any of the NI rods and find them too expensive and hard to weld with. They seem prone to lack of fusion failures. I do like using plain steel (trade name Ferroweld) sticks for making non machineable (grindable) welds on large cast iron pieces when necessary (preheat use short backstep welds, and frequently use an air chipper to peen the welds and control shrinkage) but prefer brazing WITH SPECIAL brazing FLUX, do NOT depend on flux coated rods to provide enough flux.
7) Why are welders even talking about clamps and overlapping type joints. Butt welds are almost always a superior joint.
Just my .02 YMMV

Please excuse this quick post as I have only scanned the current crop of cast iron welding threads and do not want to directly address any specific replies, but there are a couple of simple points that I think need to be made. All the following is just IMHO.
1) The exhaust system was welded during manufacture which seems to indicate that it can be welded during repair.
2) The photo is not enough of a close up for me to tell accurately but it seems to be a plain long radius pressure piping elbow which should be available at any quality industrial plumbing supply. These elbows are designed to be welded and usually come pre-bevelled. The long radius elbows are less common and more expensive than the short radius elbows. Both are also available as 45s and often as 22 1/2s but the 90s can be cut to any angle. They are not really expensive and are really handy for truck grill guards and handrails (1 1/4"). They are much cheaper and easier and faster to use than a pipe bender.
3)Fixation on welding cast iron is most common amongst the most inexperienced welders. Most of what people think is cast iron is really cast or forged steel. The easiest way to tell is to try to cut it with an OA cutting torch, if it cuts its steel, if it just melts and blows away then it is probably cast iron. This is much easier and a better indicator than a grinding spark test.
4) 6010 (6011 on AC not nearly as nice as DCRP) is IMHO the only real way to get a full penetration weld on pipe but without root grapes inside which can reduce or obstruct flow. Really good guys can sometimes do roots with 7018 DCSP on larger pipe, but few bother to try. I have never found a use for 6012. 6013 is handy for many special uses but IMHO is not a very good GP rod. 7018 is by far the best GP rod, (if your box won't run 7018 put major effort into finding one that will.)
5) Small pipe is harder to stick weld than big pipe, IMHO pipe smaller than ~1 1/2 or 2" is easier to weld with OA (or TIG), I like uncoated HT rod but I do remove the oxide with sandpaper before use. OA gas welding uses the same rod manipulation technique as TIG, and is great TIG practice
6) I seldom use any of the NI rods and find them too expensive and hard to weld with. They seem prone to lack of fusion failures. I do like using plain steel (trade name Ferroweld) sticks for making non machineable (grindable) welds on large cast iron pieces when necessary (preheat use short backstep welds, and frequently use an air chipper to peen the welds and control shrinkage) but prefer brazing WITH SPECIAL brazing FLUX, do NOT depend on flux coated rods to provide enough flux.
7) Why are welders even talking about clamps and overlapping type joints? Butt welds are almost always a superior joint.
Just my .02 YMMV

I have the plans for a heavy duty muffler made from 3" OD heavy wall tube, an 1-1/4" input and output tube going through the center, and 4 washers 3" diameter with an 1-1/4" main hole and suitable small holes. Small tube goes straight though, there is a slot cut in the middle with a blocker plate welded in. Easy to scale to the size you need, 4x the wall thickness for the cheap mufflers.
William Wix>> Hi folks,

I think it would be less expensive to make a new flange and get a muffler shop to bend a new tube for you. 309 is a nice stainless rod with very high levels of nickel and chrome. But not cheap. Check with you welding shop for prices.
Dan

Given the sheer bulk of this engine (a 7 hp engine which weighs about 200 lbs), I'd be surprised if the manifold reached a dull red. If it did, I could well believe that the microstructure would change. We'll have to see when I get the machine going.
Chris