How to Repair a Cast Aluminum Transmission Case with a Handheld Torch
Note: Due to the thickness of the aluminum, we recommend using oxyacetylene torch and a size 3 or 4 tip. Propane or MAPP gas will not heat the large mass of aluminum sufficiently to flow the rod. Super Alloy 1 will not bond to cast aluminum, Super Alloy 5 is required for this application.
Prepare the cast aluminum transmission case by beveling the crack with a grinder. Beveling is necessary to achieve full penetration of the aluminum filler rod, which replaces the removed material and bridges the gap.
Broadly preheat the cast aluminum with the torch, front and back, continually moving the heat. The base metal will look soft and begin to dimple as it reaches the working temperature. Apply the flux with the end of the rod and watch the transformation from powder to liquid, indicating the cast aluminum has reached the 600°F working temperature. Add more rod and flux, flowing the deposit before applying to the next section. Work your way down the part, filling the gaps in the cast aluminum incrementally until the entire crack has been filled.
This cast aluminum transmission case was repaired in less than 2 minutes with roughly $1 of Super Alloy 5. The resulting bond is strong–30,000 PSI–and Super Alloy 5 can be drilled, machined, tapped, threaded, bent, anodized, or plated and is a perfect color match to the aluminum.
- Always keep flux bottle close to the repair area, because every time you move your torch away the aluminum drops approximately 100 degrees per second
- Always angle torch in the direction of the crack
- Thick aluminum requires oxyacetylene, oxypropane, oxynatural gas, or oxyMAPP gas to heat the base metal to the required 600°F. If the flux is not liquefying, it is because the base metal is not hot enough