What's inside
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Why aluminum gear housings are difficult to repair
A cracked aluminum gearbox housing can look like a straightforward TIG job, but the weld itself is only part of the problem. Cast housings often hold oil, grease, corrosion, and dirt deep in pores and seams. Heat brings those contaminants to the surface, where they can cause black soot, pinholes, and a weld puddle that refuses to behave. The housing may also distort if too much heat goes into a thin wall near a bearing bore or machined face.
Before choosing a welder, check whether the housing is actually weldable. Identify the alloy if possible, inspect the crack’s full length, and confirm the repair will not compromise alignment or a safety-critical mounting point. Some castings are badly contaminated or too thin for a dependable repair. For a housing that locates shafts or bearings, plan to check alignment after welding; a sound-looking bead does not prove the bores stayed true.
What the welder needs to do
For most aluminum repairs, look for AC TIG with adjustable AC balance, AC frequency, and a foot pedal or fingertip amperage control. AC helps break up the oxide layer on aluminum. Balance lets you trade cleaning action against penetration, while frequency affects arc shape and focus. These controls are useful, but they cannot make dirty casting weld cleanly.
For a modest housing, roughly 150–200 amps is often enough. A larger machine with a 250-amp output gives more headroom for thick sections and preheating, but it costs more and may need a 240-volt circuit. Verify the machine’s input requirements and duty cycle, not just its advertised maximum amperage. A 200-amp welder rated for a short duty cycle may need frequent cooling breaks during extended work.
Choose a machine with a stable low-amperage start and useful pedal control. Those matter when finishing a bead near a thin wall or easing off heat at the end of a crack. High-frequency start is convenient; it avoids touching the tungsten to start the arc. A water-cooled torch is generally unnecessary for occasional repairs, while a quality air-cooled torch is simpler and cheaper.
Welder options for this job
| Type | Best fit | Trade-off |
|---|---|---|
| AC/DC TIG, 200 amps | Small and medium housings, shop repair work | May lack headroom for thick cast sections or sustained high output |
| AC/DC TIG, 250 amps or more | Thicker castings, frequent use, larger work | Higher cost, often needs a stronger 240-volt circuit |
| AC/DC TIG, 200 amps with pulse | Heat-sensitive or thin sections where controlled puddle timing helps | Pulse is not a substitute for cleaning, fit-up, or operator control |
For a first serious machine, compare 200-amp AC/DC TIG welders with a foot pedal. A basic AC/DC unit is fine if it has reliable starts, adjustable balance, and local service or available consumables. Do not pay extra for pulse unless you have a real use for it; the operator still has to manage heat and contamination.
If you expect to weld thick sections often, shop 250-amp AC/DC TIG machines and check their input power carefully. A 200-amp machine can still repair many housings, especially with controlled preheat, but it may struggle to maintain a fluid puddle on a heavy section. Conversely, a larger welder will not solve oil-soaked porosity.
Prepare the housing before striking an arc
Remove oil and grease first, then strip paint, oxide, and embedded dirt from both sides of the crack. Use a dedicated stainless brush on aluminum and keep it separate from steel work. Solvent cleaning alone is not enough: it does not remove oxide or contamination trapped in the casting. Do not weld a sealed cavity, and remove nearby seals, bearings, and flammable residue where practical. Use ventilation and follow the cleaner’s safety instructions.
Stop-drill the crack ends if appropriate, then bevel the crack enough to reach sound material. A narrow surface bead over an unrepaired crack often leaves the root intact, so the crack can reopen beside the weld. Preheat may help drive off moisture and reduce the temperature difference across a thick casting, but use a controlled method and avoid overheating. A torch flame can deposit soot or heat one area unevenly.
Use filler suited to the base alloy and service conditions; 4043 is commonly chosen for many cast aluminum repairs because it flows well, while 5356 may be appropriate for some applications. Neither is universal. For an unknown casting, test on clean material from the same housing or consult a qualified welding source. Clean the filler rod too, and keep it covered between passes.
Know when to stop or choose another repair
Porosity that continues after cleaning, black deposits in the puddle, or a crack that branches through a bearing boss are warning signs. Repeatedly turning up amperage usually makes the damage worse. If the casting is saturated with oil or the repair must preserve precise shaft alignment, replacement, professional machining, or specialist repair may be the better choice.
Buy a 200-amp AC/DC TIG welder for occasional housing work if your parts are moderate in size and your electrical supply supports it. Step up to a 250-amp class machine when you regularly work on thick castings or need more thermal capacity. In either case, budget for a good torch, pedal, gas setup, clean tungsten, and practice material. Those details, plus careful cleaning and crack preparation, have more effect on the result than a long list of machine features.