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The Most Complete Source of Information on the Miller Big 40 Welder
Here at Weldmart, we love the original Miller Big 40 engine drive welder. We do not see many come through our shop (mostly engine problems); they are simple to work on. They will put out 400 amps, which you need to arc gouge with a 1/4 inch carbon. No non-repairable PC board to control anperare, just a replaceable big ugly rheostat! This machine will not weld pipe like an SA200, live with it!
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When you have to heavy gouging and welding, big rod (5/32" 7024) you can just pour metal! Ay, one time, you could get those big "Jet-Rods" in 36" lengths. You can weld 3/16" intershield or gas shielded wire.
The #1 reason to have a Big 40 is the Continental F163 engine! Miller, set it up right? Run the engine at 1800 RPMs, with much more torque. Prestolite points distributor, big paper element (that's why the seals don't leak). Last year (2025), a customer stopped in for points. He told me he bought his new Big 40 in 1980 (45 years old), no oil leaks! As he informed me, Millers don't leak! He is right, it's the same engine that's in the Sa200-F163 and the SA250-F163.​
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If you're using Miller Electric service, you're not going to get much help. These machines are older than most of the employees! In fact, most service technicians in the field have little experience with this technology (No PC boards!). So many of the new mechanics have never worked on a carburertoed engine, much less an L-head Continental!
