Weld a Cast Iron Engine Block with Crack-Free 77

How to Weld a Cast Iron Engine Block with Muggy Weld 77 cast iron welding rods

Muggy Weld customer Mike Timm purchased a 2004 Jeep Wrangler with 212,000 miles on it.  When Mike purchased the vehicle he noticed the motor had a low knock, but he continued to drive the jeep for a couple hundred more miles before repairing it. The knock turned out to be a broken piston skirt that had punched a hole in the side of the block. After researching the cost of a crate motor, Mike decided to rebuild the original cast iron engine block.

Mike thought he could hire someone to weld the block, but he made a few telephone calls and was surprised to hear a “No” from every weld shop he tried. With no professional cast iron repair options available, Mike took the attitude “What do I have to lose?” and purchased a kit of Muggy Weld 77 cast iron welding rods.

Mike used a standard old Lincoln arc welder and a quarter inch thick mild steel plate to cover the hole. He first tacked the steel into place with the 77 cast iron electrode and welded side to side to prevent the cast iron from getting too hot.

The patch fused in easily Mike welded the seam closed within minutes, with no special tools. Mike dropped the engine off at a machine shop and they found no problems with the patch. After magnafluxing the block, it passed with flying colors.

We’d like to thank Mike for restoring his cast iron engine block, for sharing his photos, and for not taking “No” for an answer.


  • For best results clean and bevel the cast iron before welding
  • A bright shiny surface by grinding or sanding disk is optimal for the best penetration
  • Gently pre-heat the cast iron if possible. The weld will lay flatter when you first start your bead and preheating removes moisture out of the cast to prevent pinholes and porosity
  • If the rod undercuts, turn your amperage down
  • If the rod looks ropey or doesn’t penetrate, turn your amperage up
  • Drill holes at the end of any cracks to stop propagation

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