How to weld repair cast aluminium

weld repair cast aluminium aluminum

Sometimes ancient motorcycle parts have lived a tough life.

Cracks or damage in parts is a possibility you might have to deal with.

In this case, the rear motor mount on my old Ironhead Harley Davidson Sportster had a crack in the fillet of the bracket.

I’ve got three of these engines from the ’70’s and they all have the same cracks in the motor mount.

These motor mount brackets are available to purchase – at a reasonable price – however the engine cases need to be split to remove the bracket. It becomes a BIG job.

So I decided we’d tackle a weld repair on this cast aluminium (“cast aluminum” for my North American friends) bracket.

The basic steps required are:

  1. Grind the crack out – I used a die grinder with a carbide burr to make quick work of the crack.
  2. Select a suitable filler – I used a 4043 alloy, but check with your local supplier what would be best.
  3. AC TIG weld the crack, filling it with new metal.

Will the repair last, or will it crack again? I have no idea, but this bike might only do 1000 miles in a year. I’m sure it will last another 20 years.

It was a quick and easy repair and saved a ton of hours splitting the engine.

You can use the same process to repair deep gouges or scratches in a part. Here’s an example where I repaired damage to a rear drum cover plate: https://www.instagram.com/p/bV93zKgarx/

If you want lots more detail how I performed this repair, I have a MUCH MORE detailed version of this video on my training website: https://learn.krankengineering.com/how-to-weld-repair-cast-aluminium

Related to this video

Other videos and articles in the “Welding and Fabrication” series:

  1. Essential tools for metal fabrication: https://krankengineering.com/tech/essential-tools-metal-fabrication
  2. Introduction to welding: https://krankengineering.com/tech/introduction-to-welding/
  3. Ultra basic overview – Arc welding: https://youtu.be/nr1z1VBToyM
  4. Ultra basic overview – MIG welding: https://youtu.be/9l50t-XsBt4
  5. Ultra basic overview – TIG welding: https://youtu.be/OXr05f3Dwsg
  6. Your first TIG welding lesson: https://krankengineering.com/tech/first-tig-welding-lesson/
  7. How to weld repair cast iron: https://youtu.be/xbLZQCOV9jg
  8. Getting started with metalshaping – beater bags & mallets: https://youtu.be/_FTH9dsxoZw
  9. Getting started with metalshaping – tucking forks: https://youtu.be/_FTH9dsxoZw
  10. Getting started with metalshaping – making a shrinking bowl – part 1: https://youtu.be/-MqEKY0gBYg
  11. Getting started with metalshaping – making a shrinking bowl – part 2: https://youtu.be/gg1fU-eqUjA
  12. Getting started with metalshaping – hammer and dollies: https://youtu.be/zYuqNybZ8IE
  13. Getting started with metalshaping – slapping hammer: https://youtu.be/sf81yqLUrwg
  14. How to QUICKLY layout bike lines with a wireframe buck: https://youtu.be/_wUf6Jj9za8
  15. How to anneal aluminium: https://krankengineering.com/tech/how-to-anneal-aluminium/
  16. How to fabricate a motorcycle luggage rack: https://krankengineering.com/tech/how-to-fabricate-a-motorcycle-luggage-rack/?

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Matt McLeod

About the Author

I teach people how to build custom motorcycles by helping them build skills and confidence with my coaching, articles and training videos. I provide better technical information for custom motorcycle builders. And I shorten the learning curve getting you there.


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