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Rehab of a very tired Millermatic 200..

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  • #31
    Originally posted by Ps91-rick View Post
    So is it safe to assume that Miller hasn’t changed their back-end that each machine has in years if not ever? I was poking around my machine a bit and started taking my gun apart a little and ultimately cut the brass machine end off the liner as it was snapped in half anyway and at some point I’ll have to find a way to extract the threaded piece from the fat machine end (whatever it’s called).. For now I’ll be looking to get a new-to-me gun.

    My point here is that even though my machine is 40 years old I can still buy ANY gun with a miller backend and it will work just fine with my 40yo machine.. is that correct?

    Thx!! I’m waiting for my parts to be shipped/arrive care of Miller4less..

    Here’s a few gun pics for you.. I gather I’ve got the 400A model of Tweco.. and Yes, the first picture is showing the bent piece that has been snapped in half by a PO.
    Since Miller went to the modern style of gun the back end has stayed the same, but there are slightly different looks to them from various manufacturers. Some you'll see a brass nut and a small section of liner exposed and that lines up with the wire feed. On others there is a tapered brass cone that covers all but the last tiny bit of liner, which still lines up with the wire feed. That part doesn't matter much, and the important stuff like where the ports for the gas are located, diameter, etc are all the same.

    The older style of gun looked very different and was no longer used even before the 200 was released. Going off memory from what I've read here it was some point in the later Millermatic 35 run when they switched to the modern gun. They had a large shroud that covered a separate gas line, liner, control wires, etc. The gas valve was actually in the torch handle, so no internal gas valve/solenoid.

    Anything along the lines of an M-25 or aftermarket equivalent will be perfect for your 200. I've even modified older MM35S and 35 to use an aftermarket M-25 gun and it works out really well. The nice thing about the M-25 is that they're so common you can walk into virtually any welding shop and get consumables for them and the online sources are nearly endless. I won't knock Tweco or Bernard guns, but for hobby use I don't think they're worth the extra expense.

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    • #32
      My MM200 is just a little newer than yours (JG028277). I looked at the parts list for both my ser no and yours, and both refer to the GA-20C gun with reference to the same gun parts list manual OM-1025. So, it looks like the guns are the same. I replaced the GA20 with a Bernard Q-series; plugged right in. I have also had a Tweco gun on it with the standard Miller fittings, so I agree with Bushy--no reason a modern gun won't work on your machine as well as it does on mine.

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      • #33
        Awesome.. for now I’m going to get another gun with the assumption that I can put a power plug on this, make a ground cable/clamp and plug the new gun in a give it a try hopefully (after I put the new parts on obviously).

        I still need to figure out how to mount the wire feed spool since I’ve got nothing but the shaft.. I just looked up all the parts associated with the feed spool holder and they still sell all those pieces.. (parts 47-53) in the parts diagram and all appear to be available which kinda surprises me.. for $65..

        Is there any benefit to taking the wire feed drive apart for cleaning?? Mine, as mentioned earlier, is a bit corroded and I obviously can’t see all sides of it.. I was thinking about removing, cleaning — getting the corrosion off it and maybe some lubing possibly on the moving parts if needed and put it back together.

        By the way.. Should I replace the rubber gas line that runs from the back of the machine and over to the wire feed mechanism? I don’t know if it’s something that ought to get replaced once in a while.. I don’t want to find out its leaking...

        You all are a wealth of information and I’m super grateful to you all for your knowledge, guidance and patience with my dumb questions!!

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        • #34
          Originally posted by Aeronca41 View Post
          My MM200 is just a little newer than yours (JG028277). I looked at the parts list for both my ser no and yours, and both refer to the GA-20C gun with reference to the same gun parts list manual OM-1025. So, it looks like the guns are the same. I replaced the GA20 with a Bernard Q-series; plugged right in. I have also had a Tweco gun on it with the standard Miller fittings, so I agree with Bushy--no reason a modern gun won't work on your machine as well as it does on mine.
          I went and dug up the reference to when the gun changes happened. Miller Kevin, a moderator and tech here, said that the switch to the GA-20C happened at the end of the model 35 run in 1980 (JA448186). From that point forward the back end has remained the same.

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          • #35
            That's good info, Bart. Thanks for digging it out.

            As to disassembling the wire feed mechanism-two schools of thought on that. 1, if it's not broke don't fix it. Many things that weren't broken before, are after being "fixed". 2, if there is any binding due to corrosion from the obviously damp environment your machine was in, it will add extra drag and thus more load on the unobtanium wire feed motor. I hold to both schools, depending on the situation. My two cents worth here is that if it were mine, I would probably take it apart and clean it up. Good insurance against shortening the remaining life of the drive motor.

            On the hose, I would think it would depend on what kind of shape it appears to be in. If it's obviously cracked, I'd change it. One, in my estimation pretty unlikely, possibility is that the inside liner might have started decomposing over the years. I have on occasion held a clean white rag loosely over one end and blown some air through it from the other at very low pressure and velocity and see if you see any particles coming through. Only ever found one case of that in 50+ years of messing around with electrical and mechanical equipment. Mine is still running on the original factory hose. My guess is it is probably not a problem.

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            • #36
              Ok.. so I spent some time in the sun with the miller outside where I had TONS of light in spite of the rain we’ve had these past few days here in LA.

              Anyway, I received my first order of parts from miller4less and installed the new high/low voltage plugs (yellow) that the selector cable plugs into on the front panel. I also removed the old gun ground plug to replace but haven’t yet done that..

              I need to get an air tool to use to clean up the various contacts that I’m touching to make sure they’re making good connections.. So for the moment the two yellow plugs are installed but unhooked on the backside.

              After looking closer at the selector cable that I’ve shown in other pics, I tried to remove the end male plug using the Allen wrenches but they’re rusted pretty good and since the cable wasn’t looking that great and had a slice through the outer insulation, I decided if at all possible, to build a new one. This is the cable that’s about 2’ long and the other end of it attaches to a copper block on the contactor (??).

              If you have any thoughts on building the cable that haven’t already been mentioned.... At this point I’ll assume I can use stranded 4 gauge like for the missing ground cable... but I guess it could be 3 gauge but the docs don’t seem to mention anything about this one cable — they show it but give no part numbers that I saw... I’d rather over-spec than under — as long as I can re-install it through the panel. I’ll see about getting a new plastic strain relief for the front panel for the new cable..

              Here’s a few pics for ya..

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              • #37
                At 200 A, 60% duty cycle, I think the normal recommendation is #3 for welding cables, but that is good for up to 100'--you're going a few inches. #4 is fine--whatever you have on hand; if you have some #3, I wouldn't go out and buy #4--bigger won't hurt, obviously, but it's not needed. Just get the connectors and make it. To protect the cable where it goes through the panel, you can split a piece of small rubber or plastic hose lengthwise, cut it to length, slip it around the hole, and have an instant home-made grommet--no need to search around for a pre-made one. if you are concerned about strain relief, just put a small hose clamp around the cable behind the panel to keep it from pulling through--not too tight so you cut through the insulation, and then tape it up so it can't hit any live connections if the cable should be pushed through the panel from the outside. Or just ignore all that and find the right strain relief and it will look like a new one.

                If you want to mess with it, a little heat might break those screws loose in the brass connector. Maybe a heat/cool cycle or two.

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                • #38
                  I've removed a number of recalcitrant welding connectors. I first find a tight-fitting 1/2" or 3/8" drive bit for the set screws - which could be american, metric, or torx, depending on how rusty the screws are, pounded in with a suitably large hammer. Do the hammering now, while it's cold, then remove the bit and keep it handy. Then I hit the connector with a torch until the wire catches fire and burns the insulation back for several inches from the connector. Then I plunge the connector in cold water and swish it around until the bubbles stop. Into the vise, and attempt to loosen the screws. If the screws come out, good. If they strip, find another bit that will fit the new size head with a suitable hammer, get it even hotter, and try again. When you put them in again, using whatever bit now fits them, use plenty of copper antisieze, so they come out the next time.

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                  • #39
                    Ok.. I got a little bit of time this afternoon to do a little work..

                    I focused a bit on the part of the machine that threads the wire through the nose of the hose where the gas is injected. I was able to clean up some of the rust/corrosion on some off the little parts such as threads, washers, and the like.. In the attached photo I was able to cleanup the lock-down hardware for the moving wheel (I don’t know the names of these parts — sorry!). The brass nose that is on the left of the image sticking out looks a bit odd to me .. I was able to remove it with a bit of persuasion. The pointy end that pops out above the motor gear seems a bit boogered up.. I don’t know if that will effect anything or not.. I’m guessing probably not. Anyway, I got things a bit lubed up on the moving parts and it seems a lot better.

                    On the other hand I received my parts to put together the spool holder that was missing.. I forgot to take a picture once I put it back together.... And unfortunately I forgot to order ONE keyed washer for the whole thing.. Doh!!

                    Anyway, little by little.. I really need to scrounge up some of that 4 gauge wire.. Someone suggested RV places might carry it as they use it for Solar installs.. but I’ll probably just order some online somewhere. enjoy your weekend all!!

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                    • #40
                      For heavy wire online, I usually use "acdcwireandsupply" on ebay. Your local welding supply place should also carry it, as will most battery supply places (when not ordering online, I get mine from interstate battery), some auto electric places, etc.

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                      • #41
                        "Tractor Supply" carries welding wire.

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                        • #42
                          Originally posted by Ps91-rick View Post
                          Ok.. I got a little bit of time this afternoon to do a little work..

                          I focused a bit on the part of the machine that threads the wire through the nose of the hose where the gas is injected. I was able to clean up some of the rust/corrosion on some off the little parts such as threads, washers, and the like.. In the attached photo I was able to cleanup the lock-down hardware for the moving wheel (I don’t know the names of these parts — sorry!). The brass nose that is on the left of the image sticking out looks a bit odd to me .. I was able to remove it with a bit of persuasion. The pointy end that pops out above the motor gear seems a bit boogered up.. I don’t know if that will effect anything or not.. I’m guessing probably not. Anyway, I got things a bit lubed up on the moving parts and it seems a lot better.
                          Sounds like good progress!

                          The round wheels with three screws are the drive rollers. The brass nose on the left is called a wire guide. The end of the gun has a brass guide fitted to it as well (some brands just have exposed steel coil that does the same thing). The whole system is designed around having the wire supported with almost no gaps from the area it enters the wire guide on the left to the gun end on the right and keeping it aligned with the grooves in the rollers. Any area unsupported is a potential for causing a bird nest so they keep them small. The drive roll is adjustable in/out with a screw....you feed the wire through to the gun, then make sure it's aligned with the groove on the roller, and adjust the roller as necessary. The top roller housing has some in/out play so you just sort of wiggle it in/out until you feel it grab the wire and then set the spring lever.

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