Bodywork Basics

Rescue doomed components with some very sensitive welding

Weld cracked alloy castings.

Welding any sort of casting can be a very humbling experience. No matter how far you think you’ve progressed as a welder, a casting can bring you right down to earth in a filthy puddle of molten metal and disappointment. Cast iron is brittle, so if a localised area expands or contracts a smidgeon more than another, it’ll take great delight in cracking. This will usually happen exactly where you’ve repaired it and with perfect comic timing. Cast aluminium, meanwhile, will have soaked up dirt like a sponge and this will ooze into your weld and make it horrible.

Cast aluminium is used for engine blocks, cylinderheads, manifolds, transmission casings, sumps and many other things. The biggest issues when trying to weld it are what other ingredients were added to create the alloy and what contamination it’s been subjected to. Most castings will have contained lubricant, fuel or antifreeze, which will have soaked into the structure. The heat will cook out these contaminants, which will affect the weldability and the strength of the finished weld.

The casting we’re going to repair is an aluminium manifold. It’s spent more than half a century absorbing corrosive exhaust gases, so it’s about as challenging as it gets. It’s interesting to note that a professional welder turned down this job. There was therefore nothing to lose in having a go, as the only other solution would be to find a replacement. Although the outcome of our weld was ugly at best, it was a success. Follow this process and there’s every chance that your results will be better.