Good afternoon all, I got out one of my US Army National Stock Number (NSN) 7310-01-113-1285 "Burner Unit, Gasoline, Model M2A" this morning for a photo-session for my October SoTM entry. This particular unit is an M2A made by Armstrong Products Corporation in 1977, making it just slightly newer than I am. It is equipped with the safety device, so technically, it's an NSN 7310-01-113-9172 "Burner Unit, Model M2A, With Safety Device". It is a gasoline (petrol) fueled pressure stove rated somewhere around 55,000 BTU/hr, or just over 16,000 Watts. On top is a 2 pint Valor 55 stove so you can get an idea of the size of this thing! It is sitting on a wooden stand I built to get it off the ground so I don't have to bend over so far! Some may remember my recently post on my US Army Modern Burner Unit (MBU) Version 3 (V3) stove here: US Army Modern Burner Unit Version 3 (MBU V3) If you've read that post, this is the burner that was replaced by the MBU, and it's designed to be used in the M59 field kitchen range. In doing some research on the unit, some folks in the Army called them "M2 Bomb Units" as apparently, they had a history of explosions and other accidents. I never did find out what caused the accidents, but I can make several guesses based on info I've found in the Army's Preventative Maintenance (PM) Magazine and other publications. Of course, what I'm going to share are just conjecture on my part. As can be seen by the name itself, the M2A is a modification of the M2 stove...and the M2A with "safety device" is a modification of the M2A stove itself. That safety device consists of a fuel tank over-pressure relief valve, set to about 60 psi or so, that would vent excess pressure from the fuel tank into the base of the burner. The M2A does have a pressure gauge that has green, yellow, and red areas, and the manual talks about the importance of never running the stove in the red. I suspect that the first cause of accidents was over-pressurization of the stove, leading to a fuel tank rupture and fire / explosion. Another likely cause of accidents is the design of the M59 field range. From what I understand, it can be configured in different ways for different cooking tasks, and the M2A (and MBU) can be installed in different "shelves" at different vertical heights inside the range. There are warning stickers on the range saying that only one M2A / MBU should be inserted at once, so I suspect another cause of accidents were folks installing a lit, running M2 stove underneath a non-running stove when not paying attention...with the lit stove then overheating the unlit stove until an explosion occurred. I suspect many of the accidents were due to misuse than faults with the stove. (although, as we'll see, the design is not faultless.) These are very interesting stoves. The long tubular unit across the top is the generator, and it is massive compared to anything else I've ever seen. Even the Coleman 457G Handy Gas Plant / Heatmaster rated at a similar 35,000 BTU has a tiny generator tube in comparison, maybe 10mm in diameter. The one on the M2A has to be somewhere around 50mm in diameter. The design is both excellent and terrible. As the other gallery post notes, they have a pre-heater burner for heating up that massive generator that itself needs pre-heating. However, the pre-heating burner is mounted at a 45 degree angle, making the spirit cup pretty much useless. Thankfully, burning gasoline, they don't need a lot of pre-heating, so a few seconds with a propane torch and they light right up. There is no fuel shut-off between the tank and the inlet side of the generator. So if a fault occurs, the only way to stop fuel flow from the tank is to depressurize the tank itself. The vapor metering orifice and fuel valve is built onto the generator assembly. This is both good and bad. It's good that when you install a new generator, you have a fresh valve and orifice. It's bad in that as the generator heats up, it thermally expands, getting longer, and if it gets hot enough, it could pull the orifice out of the manifold, shooting vapor places it was not supposed to go, likely causing a fire and perhaps an explosion. The manual doesn't explain this, but when I replaced the generator in this unit after disassembly for cleaning, I ensured that everything was adjusted so that the orifice was pushed as far as possible into the manifold. The design of the tank over-pressurization valve is interesting. I'd expect that in an over-pressure situation, venting fuel vapor from the tank into a running stove manifold would be very exciting / terrifying...likely causing a huge flare-up? I'm not sure, it almost might put the stove out as the raw fuel vapor would cause a *very* rich fuel/air mixture in the burner? I really don't want to find out. Of course, on the good side, like many of the Classic Camp Stoves that we all love, it can be fettled with only the most basic of tools - screwdrivers, and adjustable wrench/spanner, etc... There are no electronics unlike the MBU, so I expect it will be operable long after the last MBU has died from bad capacitors or other problems. I also like how the stove has provisions to mount two spare generators...so if one does go bad, you've got two more. This stove required a LOT of fettling to get it working. I bought it CHEAP on the e-place, paying about twice in shipping over what I paid for the stove. It came with a spare fuel tank, for reasons that will soon be obvious. It needed a new burner tray pan (the stainless steel part surrounding the burner) which was also found cheaply on the e-place. The original fuel tank was a DISASTER. I think fuel had been left in the tank since it was built in 1977, so rather than try and clean out the tons of garbage inside, I just replaced it with the brand new spare tank. The original over-pressure relief valve had a copper tube going from the valve to the burner manifold which prevented fore/aft adjustment of the burner, and then proper mounting of the generator - there was a sizeable gap between the generator valve and orifice and the manifold. The tubing was cut so short that there was no way to get a good fit. I ended up replacing the copper line with a piece of very high-temperature rubber hose (Viton, maybe?) so I could now adjust the fit of the generator properly. The pre-heater was also a disaster, as someone had tried to start the pre-heater with that icky gasoline in the tank. It was removed, cleaned, and tested fine. The original feed pipe from the tank to the generator was also a mess since it had been dipped in the original icky gasoline for a very long time. Thankfully, while it had some corrosion, it cleaned up and was reusable. Starting one of these units takes a long time and some finesse. Of course, you've got to fuel it and give it some pressure with a tire pump. 6 to 8 psi per the instructions, and "use a hand pump only." You can see I've got a propane torch, it makes lighting the pre-heating burner very easy. That should do. As you can see, being that there are no finer graduations on the gauge other than 10 psi, it is somewhat of a guess. Those with good eyes may be able to tell that the gauge says "MADE IN SPAIN." Interesting. Up next, spin the lever on the pre-heating burner, pre-heat the pre-heating burner, and light it. It was sunny this morning, so even in the shade, it's very hard to see the pre-heater burner flame, but maybe you can see a little orange at the top of the photo and some blue inside the burner bell? The stove has a cover that gets installed over the pre-heating burner and the front half or so of the generator. This is a nice touch, without the cover it takes much longer to pre-heat. And even with the cover, pre-heating takes a LONG time given the size of that generator! The manual says to pre-heat until the far end of the generator is hot. Took me about 20 minutes this morning to get it hot. To light it, I remove the preheating cover, leave the pre-heater burner running, place a flame by the burner, and open the fuel valve. It usually takes a few seconds for vapor to get out of the massive burner. The light-up can be quite exciting. In the above photo, it's lit, but burning fairly poorly almost as if I didn't pre-heat it enough! Per the manual, it should ignite off the flame in the pre-heater, but that doesn't seem to work all that great for me. Of course, once the main burner has lit, turn off the pre-heater. Here is another bad feature of the stove. If you haven't heated it enough, you'll get liquid gasoline out of the orifice. It drools out the front of the stove, and can catch fire. Ask me how I know. Once the generator is fully heated by the flame, you can adjust the fuel/air mixture with the rotating damper on the stove. Fuel/air mixture damper fully closed to fully open. Once fully up to temperature and with the mixture set right, it burns with a very nice blue flame. It's hard to tell in this photo, but the damper is fully open and the mixture is full lean. I am running regular unleaded ethanol-free gasoline. It almost seems like it could use a little more air. I suspect that the gasoline of today is quite different than gasoline in 1977, so perhaps that's why? Some additional photos: In conclusion, it's a neat stove, but one that I don't use very much due to it's complex and lengthy starting procedure, plus it can be somewhat temperamental. While I can see how it gained the nickname "M2 Bomb Unit," I'm not afraid to use it, as I am careful and understand its problem areas. For sure, once it is running and up to temperature, with the valve full open it puts out A LOT of heat and has very close to no odor, which is always remarkable to me for stoves that are running regular unleaded gasoline. Thanks much, ben
Thanks Ben for what must surely be the definitive write-up on the M2A. It’s certainly the case that a stove’s ‘quirks’ can prove endearing to a collector but what you describe takes such to excess perhaps, particularly: If I remember correctly, that’s a ‘feature’ that contributed to Coleman taking their No.501 stove off the market and recalling those sold, guaranteeing its place in the hearts of collectors, much like the M2A no doubt. John
Hi John, I completely agree - quirks are endearing, but the M2A just has so many quirks. So many that some may find it utterly unappealing. For sure, it's not a favorite of mine, but I don't hate it either. Thanks much for the link to the 501! I knew there was a Coleman stove that had the same lack of a fuel tank shut-off leading to a recall and it going off the market...but I couldn't remember the number. The lack of a fuel-tank shut off is definitely something I keep in mind when I'm running the M2A. I did leave the M2A fueled up. I need to bottle a batch of beer tomorrow, and to do that I need a good supply of hot water for cleaning and sanitizing the bottles. Usually I just get it from the tap, but I figured I'd leave the M2A fueled up and would use it tomorrow morning for heating up the water I need. Thanks much, ben
I bought one locally a couple years ago, mine fired right up, after the long pre-heat, and mine pops off with no yellow/orange flames as your picture shows @Ben Hall Wonder if your generator is full of crud, seeing that the tank was. They put out enough heat that they are tough to stand near to. BUilt a grate out of two 413 coleman grates so I could cook on it, but have yet to take it backpacking, my wife is a lazy one and refused to carry it.
Hmmm, mine must be an M2 because it's got a small Coleman stove as a preheater. I (we, really - there was a team of us!) lit it once at Newark. What a palaver! It took at least 30 minutes but we got it going eventually and it burned for hours with a lovely flame pattern. I think filling the fuel tank doubled the value of the stove - a bit like an old Skoda before VW took over. The previous owner had welded two grills together which sits nicely on the top and supports the pans...
Greetings @Majicwrench - If I remember correctly, when I replaced the tank I thoroughly flushed out the generator...and it wasn't that bad. The pickup tube leading from the tank to the inlet side of the generator was plugged solid, so I think that actually helped save the generator. I'm about 99.9% sure that I didn't preheat it long enough when I did that start above. About a year ago, I did find a source of new old stock generators on the e-place. In the photos above, you can probably tell that one of the new generators is installed on the stove in one of the spare generator brackets. The other generator installed in the spare generator brackets on the other side I used the stove a *lot* today (probably about three hours of run-time in total) for heating up water for cleaning bottles and other beer making equipment. The first start this morning was as you described - a very long pre-heat and it lit immediately. I used an IR temperature gun and for that first start, the generator end furthest from the pre-heating burner measured 150 deg F / 66 deg C before I started the main burner. Same for the second start - slightly more than 150 deg F / 66 deg C and it lit right up. My setup. That's a 10 gallon / 40 liter or so pot on my homemade stands. The rusty black thing in the background is my trailer for my lawn tractor turned up on it's end, and propped up to make an ad-hoc windscreen. I snagged some photos after it was running nicely today: Some comments on the photos: * As the stove got fully up to temperature, the two "arms" of the burner on the right side were both even - the front "arm" looked like the back "arm". * When I got the stove, the cast iron burner was quite rusty on the left side. I did quite a bit of cleaning to remove the rust, but appears that additional cleaner is going to be required as some of the burner slits are partially blocked. If I had a tool kit for the stove, there is a "cleaning tool" for doing this. I'll have to make one. * The manual says to "Adjust air shutter until flame is green in color." I was able to do that today - with the air shutter about half-way open, I got a nice green color flame. After using the stove for about an hour, I took a picture showing how the thermal expansion in length of the generator pulls the valve/orifice out of the air shutter assembly: When the stove is cold, that hex nut is fully seated against the air shutter plate. It's probably pulled out 3mm or so? Thankfully, there is another 6 or 7mm inside the air shutter assembly, so it's in no danger of coming out, but you can see how if one was not careful when replacing the generator, and didn't snug up that hex nut against the air shutter plate, it could come free once the generator got very hot. That hex nut is part of the orifice, and is NOT adjustable. On the previous M2A I fettled, one of the generators had a weld that was porous, so I condemned it and cut it apart to see what was inside and how it was made. I tried removing that hex nut, but even with a 1/2" air impact gun, it stayed put. I should describe the innards of one of these generators, as they are quite interesting...very unlike a standard Coleman generator with just a wire spring. Probably not many people have had one that they wanted to cut apart. The generator is a horizontal tube, with coarse screens about 30mm from each end. When I say coarse, the openings are probably about 4mm in diameter, and there's probably 20 of these holes comprising each screen. Inside the length of the generator tube, between the screens at both ends, is a black-in-color substance. I'm not sure what it is, but it is porous, somewhat compressible with gloved fingers, obviously can take high heat, and fills the entire diameter of the tube. It's not metallic, and it's not stringy like asbestos or rock wool. I should note that I treated it as if it were something nasty like asbestos, and disposed of whatever it was safely. The coarse screens keep the black material centered in the tube. I should have taken some photos, but not knowing what it was and thinking it possibly could be something nasty like asbestos...I didn't pause until I had it safely removed and disposed of! Once it is fully cooled off I plan to de-fuel it and put it back into storage. Thanks much, ben
If I recall (big if) correctly, the manual has you use the edge of the preheater cover to clean the slots in the burners. Thanks for the fun post. I have a really big, square griddle, I plan on doing LOTS of pancakes at one time on mine
Hi @Majicwrench - interesting you mention a large griddle! I was just talking with my wife several weeks ago about getting a large cast iron griddle to go on the MBU, which would also fit the M2A. I'll have to look in the manual, but for sure, the preheater cover edge would be very close if not the exact correct size for cleaning the burner slots! Thanks much, ben
Ben, try using the saw blades of an Xacto knife set to clean the slots of your stove. It is what I use to clean the slots of the burner of my Handy Gas Plant. My brother who was a cook in the MC said this was Uncle Sam's answer to bad cooks, as you only sent out to light the stove those cooks who had the intelligence of a pizzle ant and even then you might be insulting pizzle ants. I often wondered how he knew how to light it. Lance
Good afternoon all, Spent some time in the garage this morning looking at / thinking about burner cleaning among other tasks. Turns out that the preheating cover steel is too thick to be used as a cleaning tool...and the manual mentions a dedicated slot cleaning tool. The Xacto suggestion from @Lance was a good one - I don't have any Xacto saws, but I do have some thin Zona saws that turned out to be too thin to be good cleaning tools. I happened to look down, saw a piece of brass sheet scrap...and it turned out to be the perfect width - just thin enough to get in the burner slots - but thick enough to give them a good cleaning...plus I know what sort of saw blade thickness to look for. So off to do some shopping. I also was working on wiring for a SouthWind 978M surplus military heater because Winter is coming...and managed to slip with a pair of small scissors cutting back cable insulation giving myself a rather nasty/deep puncture wound to my left index finger. I'm on anti-coagulants from three unexplained blood clots several years ago...and for about five minutes...was thinking I was going to be going to the local hospital emergency department for stitches. Thankfully, it clotted fine and actually is not giving me any problems with just a normal adhesive bandage. No loss of feeling, so don't believe there is any nerve damage. The hematologist is still trying to figure out my blood clots - I have no risk factors other than a previously-unknown single copy of the Factor 5 Leiden clotting mutation. My tentanus shot is up-to-date, so no worries there. After that little incident, I decided to take it easy for the rest of the day so no more playing with stoves / heaters / etc... Thanks much, ben
Ben I really like the fact your friend shown in your picture is sitting on your shoulder. How do you get her/him to stay there long enough for a photo? My cat would be off my shoulder and headed for the nearest food dish as soon as I set her up on my shoulder.
Greetings @Lance - his name is Major, short for Major Monogram, a cartoon character from the Phineas and Ferb cartoon show, named by our son when both Major the cat and Robby were younger. It's totally voluntary - he'll come back to my office/ham shack/computer room/stove workshop, put his paws on my leg, and meow until I pick him up. He *loves* to sit on my shoulder like that, and will sit there purring until something like food hitting the bowl or someone turning on the water grabs his attention. Sometimes, he prefers my lap and shoulder to even food and the water. I've never had a cat before him do anything like this. Usually, like you say, you put a cat somewhere and they leave immediately. Thanks much, ben
https://www.aspcapro.org/sites/default/files/Feline-ality%20Guide_PRO.pdf Cat personality assessment - sorry, feline-ality. Thanks to ASPCA.
I’ve got a cat who likes to sit on my shoulder, too. Lately, he’s taken to sitting on the back of the recliner when I sit in it, often with a paw on my shoulder or neck. Matter of fact, that’s what he’s doing as I write this. ….Arch
My cat pats me more than I pat him, he has 2 methods - a) stand on the back of the lounge chair and lick my head and b) stand on me and kneed whatever he's standing on like it's dough. I'm not allowed to pat him in these situations - results in a bad tempered growl. Then the tables turn and he's sitting on my lap for the payback. My daughter's cat almost tolerates people. Almost. I've seen photos of cats sitting on people while they do rock-climbing etc. My cat isn't that tolerant - but it sounds like some of yours might be. Wow - this thread has gone further off track then most. Hope that's OK!
Earlier today, I posted a SOTM entry with this stove. In the entry, I noted: I actually have two of these things...but I haven't photographed the first one. Since it was nice out this morning, I figured, why not gas it up and haul it out back for a photo session and fire up? So I did. The previously photographed unit, and the one in the entry, is a 1977 Armstrong Metal Products Company made stove. This one is a Standard Metal Products made stove, but doesn't have a date anywhere that I can easily find, yet. On to the photos! Front view. Just like the previous photo session, I've put the stove on my custom-made stand to get it off the ground. The usual photo views. Couple of comments to make on this series of photos. As can be seen, this stove has had some use over it's lifetime. The decals are shriveled up, there's a good bit of rust in places, and it has some dings and dents. The generator that is installed has been well-used. Some might note that the stove is pressurized and that the pre-heater is running. The stove generator takes FOREVER to heat up, so I figured it might as well be heating while I was taking the photos. You might be able to see tiny amount of blue flame in the pre-heater. This pre-heater was in quite bad shape when I received this stove. In fact, I thought it might not be able to be saved as it was just so rusty and plugged up with garbage. Thankfully, it was completely repairable. Overhead shot. SMP marking. When I received this stove, it was heavily rusted. So rusted that the shutter wouldn't move. So it got disassembled, rust removed with citric acid, and parts were resprayed with silver paint. This air shutter / ID tag was one such part. As can be seen, some of that new paint is missing. In one of my earlier posts, I noted that incomplete preheating results in liquid gasoline drooling out of the front of the stove. That is exactly what removed the silver paint! I didn't have it preheated properly, attempted a start, and liquid gasoline came out the air shutter and removed that paint. A close-up of some of the shriveled up decals. I forgot about the pre-heater cover, so installed it to hasten pre-heating. The top pan of the stove is held down in the four corners with four spring-hook assemblies. The spring-hook assemblies normally mounted to the frame with a pushed-in fitting made from sheet steel. Two of these were missing, and the other two were beat up severely so I had to make up replacements. I couldn't duplicate the push-in fittings, so used rivet-nut inserts into the frame and just used a machine screw. The hooks are hand-bent and the springs came from a spring kit I have on-hand. A flame shot. Running fine. Normally, in the Army, these would go into an M59 field kitchen. I don't have one of these, so I've made several racks so I can use the M2A's and their later replacements, the MBU V3. In this photo I've got the tea kettle on and am heating water with in. Took maybe 4 minutes to boil 2L of water? It is a 50,000 BTU/hr rated stove. I was able to source some new generators from the e-place for pretty cheap, as well as clean a lot of yuck out of the old generators with solvent. New generators have a plastic cap installed to protected the sealing surface. BUT, that doesn't nothing to keep dirt and water plus rust out of the threads. I 3D printed some caps as seen in the right photo to protect both the mating surface AND the threads. Seems to work okay. I thought that the plastic might melt in the heat, so far, so good. This little guy popped in to say hello. After reminding me that it was time to cut the lawn to make finding bugs and worms easier, he inquired as to what I was doing. I tried to explain but after a few words he hopped off looking for more worms and bugs. I've got several videos of the M2A running that are uploading / processing now. Will post them shortly. thanks much, ben
Second video. A little shorter, a little more zoomed-out. I really have no idea what I'm doing when it comes to a video camera. And in this case, the video camera is my iphone...
As the FNG(F&^%in New Guy) at my first duty station in Germany in the late 1980s, I became well versed in the operation of these burners and learned a LOT during that 45 day field exercise. I completed my "welcome to USAREUR(US Army Europe)" classes and went to the field the following week. The First Sergeant asked who the f I was and he said, "Oh the FNG. Since you haven't been assigned anywhere yet, looks like you'll be on KP next week and for the next 45 days." Laughter erupted from the formation. What a warm welcome it was. Haha! Between these and the immersion heaters, I learned to "get my flame on" pretty quickly. Most of your comments are spot on. But some are a little off. For instance, these generators are steel. No amount of heat these can produce will cause enough expansion to disengage the gas tip from the mixing chamber unless it was dropped off a truck. That slip fit is there specifically to allow for expansion. While you are correct that there is no shutoff from the tank to the generator, the generator and associated parts are all capable of sustaining way more pressure than the tank itself. The pressure relief is set to only vent air from the top of the tank and into the mixing chamber. While it IS flammable, it is NOT rich once mixed with air. If you disagree, add a couple tablespoons of fuel to a Coleman stove or lantern, set it out in the sun for a few hours, shake it up all you like and try to light it. It won't. It's just too lean once mixed in the bunsen/mixing chamber. Will it change the flame noticeably in these? Sure. But it's vented to the mixing chamber for a reason. The preheat generators were not preheated when we used them, even though the cup is there. If I recall correctly we just cranked the cleaning needle a few time, opened the valve a 1/4 turn, lit them, waited a few seconds, opened the valve all the way, placed the heat shield over the generator, and went on to the next one. They would warm up and settle down just fine on their own. The heat shield WOULD be sooty though. I was in an ALO-1 unit(fully manned and fully equipped for immediate deployment at all times. Any mission critical component not ready/available for over 24hr was reported to the Pentagon which was frown upon.... haha!) so parts and most other things were plentiful back then. During recovery, after every field problem, they replaced all the generators and preheat burners and threw the used ones in the scrap bin. There were other parts that I thought were just fine that got scrapped as well, though I don't recall what they were, probably pressure gauges and relief valves. The mess sergeant was a crusty Vietnam veteran who, without question, was by far the best mess sergeant I had in my entire 21+ year career. The dude could flat out cook! And he knew how to work the system to get us the best chow, even/especially when we went to the field. He said the generators were supposed to last like 400 hours of operation on MOGAS(Army leaded gasoline) but he sent us to the Esso station in town for "Super Bleifrei" or super unleaded to run the burners, milspec lanterns, immersion heaters, and yukon and pot belly stoves on. "No bleaping MOGAS!" he would shout. Sometimes, he paid for it himself. We cleaned the burner slits with single edge razor blades and wire brushes and coated everything with "corrosion preventer". I was never on KP again, but I gained tremendous respect for the work the 92Gs put in. It's a LOT of work setting up an MKT field kitchen, tearing it all down packing it all away driving for hours and lather rinse repeat, sometimes 6 or 7 times a day back then, as chemical warfare was thought to be a near certainty, we would have to move every time they simulated a gas attack, which was several times/day. Doing it in the dark under light and noise discipline with red lens flashlights, camouflage nets, tents, dish washing stations. It was an education, to say the least. First night out, they pranked me and told me to pump it up to the high end of the yellow zone, light the preheater, wait 1 minute and open the main valve. A 15 foot bright yellow column of flame lit up what seemed the entire forest, including our headquarters location, which could have been seen for probably 10 miles at least. It became immediately and abundantly clear that this was not a good thing. A very angry First Sergeant let loose an R. Lee Ermy type tirade of expletives that could probably be heard just as far away as I faced him, standing at parade rest for what seemed an eternity. Soon followed by several hundred pushups and grass drills in MOPP 2. The entire mess section was watching and laughing. That was my official welcome to Charlie 16. One that I will never forget. Those plastic caps on the spare generators need to be removed. They will melt. Why they didn't come with metal caps is beyond me. The generators were supposedly tightly packed with steel wool, though I never was curious enough to cut one open. SMP was State Machine Products out of Dry Ridge, KY. They are pretty widely known for serviceable items with poor fit and finish. Lots of sharp edges and crunchy threads. Good memories. Thanks for posting this.
