Weld a Cast Iron Exhaust Manifold with a Buzz Box

How to Weld a Cast Iron Exhaust Manifold

Second repair on Cummins exhaust manifold. Mike used a 130 amp mini welder to make the repair, to demonstrate a worst case scenario for using our electrodes.

This cast iron exhaust manifold from a Cummins diesel truck was headed for the junk pile because the shop did not have a cast iron welding rod to repair it. At a cost of $400 to replace, Muggy Weld 77 and 72 rods were an inexpensive alternative.

77 electrode has controlled penetration (ideal for machinability and non-cracking) and therefore may not be able to bond to heat affected cast iron.  In these situations, we recommend applying 72 burnt cast iron welding rods followed by 77 cast iron welding rods.  72’s high penetration anchors deep into the subsurface of dirty cast iron, sealing in contaminates, and can be used in all positions:  vertical up, horizontal, vertical down, overhead or flat.  After cladding the cast iron manifold with 72, complete the weld with 77.  77 electrodes are softer than standard nickel rods and its unique properties stretch and elongate up to 300 percent more than other rods, creating high strength, crack resistant, and porosity free machinable welds.

Note:  Prior to welding the cast iron exhaust manifold, we did not preheat the part and experienced no re-cracking when the weld air-cooled.

The 72/77 cast iron combination is ideal for trucking, bus lines, automotive, marine, heavy machinery and RV applications.  This same technique can be used to repair engine blocks, transmission housings, industrial machines and cylinder heads.



  • Always weld no more than 2 inches at a time and let cool for 2 minutes between passes. For some cast irons you may only want to weld an inch or less and let cool 1 minute between passes.
  • Low and slow is the key to a sound weld with cast iron.


NotePlease observe all AWS Safety & Health Guidelines when using Muggy Weld products.