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Thread: Reactor in a portable Miller Big 40 welder?

  1. #31
    DIY Junior Member badnewsracer71's Avatar
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    Default 1981 miller big 40

    I bought a big 40 minus alternator,I bought a used one on e-bay.there are 3 wires to hook up but i dont know where they go on alternator.please help

  2. #32
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by badnewsracer71 View Post
    I bought a big 40 minus alternator,I bought a used one on e-bay.there are 3 wires to hook up but i dont know where they go on alternator.please help
    Post a schematic/photo/spec. sheet/measurements.
    You can't tell the players without a program.

  3. #33
    DIY Senior Member Rich B's Avatar
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    Quote Originally Posted by badnewsracer71 View Post
    I bought a big 40 minus alternator,I bought a used one on e-bay.there are 3 wires to hook up but i dont know where they go on alternator.please help

    Are you referring to the battery charging alternator? I assume you are.

    You can use a GM style Delco alternator. 1 wire that is usually a little larger goes to the large post on the alternator. That wire should connect to B+. One wire would be the field excitation of the alternator and the third is probably a wire connection for a light on the control panel that tells you the charging circuit is working. Use a voltmeter. Probe the 3 wires. One is hot all the time. That is the one for the bigger post on the alternator. Start the engine and see which one of the other 2 is now B+ but was not before you started it. Your looking for a switched B+. That goes to your F terminal on the alternator. If you use a Delco internally regulated alternator you should have a post on the back for the B+ larger wire.....and a 2 pin connector on the edge of one side. One pin is F+ and your switched B+ goes there. Your third wire should go to the remaining terminal on that side 2 pin connector. You will have to try that one with a temporary jumper to be safe. Some of those machines might have an amp meter instead of a light and that could change the connections....


    I can look up most machines by serial number on the front of the machine.......2 letters and 6 numbers on one line stamped into the front panel. I can find prints and it also shows wire numbers...and all your wires have numbers on them if you look closely.....
    Last edited by Rich B; 12-06-2009 at 03:56 PM.

  4. #34
    DIY Junior Member badnewsracer71's Avatar
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    Default miller big 40

    thanks so much.that is so helpful.was afraid of hooking up wrong and burning something up

  5. #35
    DIY Junior Member badnewsracer71's Avatar
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    Default miller big 40

    I put alternator on as instructed.new battery.I checked fuse on emergency kill,the button you hold in while starting.I flip switch to on.Push starter button while holding other button in.I have nothing.I have checked all connections.This machine sat for over 4 years.Any ideas on what to check next?

  6. #36
    Homeowner Thatguy's Avatar
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    See post #32.

  7. #37
    DIY Junior Member badnewsracer71's Avatar
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    Default miller big 40

    I just found this site yesterday.Dont know how to see post #32

  8. #38
    DIY Junior Member badnewsracer71's Avatar
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    the serial # is jb 503942.

  9. #39
    DIY Senior Member Rich B's Avatar
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    Quote Originally Posted by badnewsracer71 View Post
    I put alternator on as instructed.new battery.I checked fuse on emergency kill,the button you hold in while starting.I flip switch to on.Push starter button while holding other button in.I have nothing.I have checked all connections.This machine sat for over 4 years.Any ideas on what to check next?

    You need to explain a little better what "you have nothing means". Does this mean it doesn't crank, doesn't start, doesn't charge? If it has a starter pushbutton and another button that says hold in while cranking.....that is a Murphy switch...it overrides the low oil pressure switch so the machine will crank and start. Fuse on emergency kill ???What are you referring to there??? If you have a good battery......use a jumper to see if the starter cranks....B+ to the Solenoids S terminal. If it cranks.....does it have a distributer or a mag? If it has a distributer jump B+ to the coil + side and crank it. See if you have spark. If it has a mag it will make spark unless the mag is bad or the small wires going to the mag is grounded. An old machine that has been sitting for 4 years will likely need work and I do exactly as I described to see if it will run. I would tackle the control issue AFTER I determined it was a machine that could be a usable piece of equipment. It makes no sense to buy and install parts if the machine has something major wrong with either the engine or the main electrical generating end......
    Last edited by Rich B; 12-07-2009 at 02:54 PM.

  10. #40
    DIY Junior Member badnewsracer71's Avatar
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    Default miller big 40

    I bought it for 200.00 for parts.I figured it was worth a shot to get it running.After i posted last message i found a broke wire.repaired wire,started machine,and welded with machine.I need to rebuild carb,other than that it welds great

  11. #41
    DIY Senior Member Rich B's Avatar
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    OK....I tried to put a link on here for the online Service Manual but it will not work. I am an authorized Miller Service shop and have access but it is password protected. Sounds like you got your money's worth.....

    Those carbs are very basic and usually pretty nasty after sitting for any period of time. Either a Marvel-Schebler cast iron or possibly a Zenith. They do make a universal replacement but it is a real poor setup as the linkage does not work to well with the idler.....Take the old one apart and soak it in carb cleaner for a good while and blow it out. The only gasket you need is for the top to float bowl and I try to save the old one or make one. They usually leak fuel if you don't have a shutoff on the overhead tank and shut it off after you use the machine. I worked on lots of those old tankers.......

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