Tips for Engine Repair Welding on 4 Common Materials | MillerWelds

Tips for Engine Repair Welding on 4 Common Materials

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From engine block repairs to fixing cracked cylinder heads, following key best practices can help overcome welding challenges.
TIG welding an engine block
TIG welding an engine part
TIG welds on oil pan

Repair aluminum, cast iron, steel and magnesium

Oil pans, intake manifolds, engine blocks and heads — engine components often require repair, maintenance or replacement. Whether you’re working on a car, light-duty truck or a performance racing vehicle, you may frequently encounter a cracked block or cylinder head that requires a welding fix.

The materials typically used for engine parts can present unique challenges for welding. To overcome these issues, it’s important to choose the right filler metal and keep the base material clean.

Consider four materials commonly found in engine component repair and key best practices for successfully welding each metal.


The most commonly used material in engine components today is aluminum. Lightweight and strong, aluminum runs cooler than other materials and is easy to modify. This makes it popular for many parts, including oil pans, intake manifolds, engine blocks, cylinder heads and valve covers.

The selection of the right filler metal is critical in TIG welding aluminum. Most cast aluminum engine components are made from a casting alloy called A356. When welding aluminum, anything higher than 150 degrees Fahrenheit is considered a high-temperature application. To reduce the potential for cracking, choose a 4000-series filler metal that is considered a high-temperature alloy, such as 4043 or 4943.

One common mistake in aluminum welding is to use a filler metal with a higher manganese content, such as 5356. While this is a higher-strength filler metal, experts don't typically recommend it for use in high-temperature applications because the higher manganese and magnesium content can result in a weld more prone to cracking.

Another challenge: aluminum castings tend to be more porous, which impacts how long you can weld before pulling oils and contaminate material into the heat-affected zone. This makes it very common to stop and start frequently in order to keep the area cooler or to re-clean the area between passes.

Welding power sources with inverter technology and variable frequency controls, like Dynasty® 400 TIG welders, provide advantages for welding aluminum. You can easily fine-tune the arc by adjusting the output frequency, allowing you to focus the heat and reduce the welding bead size.

Reducing the heat-affected zone with a tighter, more precise arc also helps save time in post-weld grinding and cleanup.

Cast iron

Cast iron can be more prone to cracking, so it’s important to watch the heat input during welding. Use a TIG rod that is high in nickel content, such as Ni99 or Ni55.

The quality of the casting determines how porous a cast iron part is. The more porous the casting, the more difficult it is to weld cast iron properly.

This makes cleaning cast iron parts critical. Soak cast iron parts in a hot tank to boil out some of the oils often embedded in the material. If you are working on a cracked or broken part, follow this step by using a carbide cutter to cut out the cracked area and clean it with an acetone or non-chlorinated parts cleaner.

Because cast iron doesn’t transfer heat well, the heat can stay built up in one area during welding. Anywhere in the part where cold meets hot, quench cracking can occur. This is when the cold area pulls heat way from the weld zone, ripping the weld apart as it cools. Slowly pre-heating the component to at least 500 degrees Fahrenheit before welding can help address this. But, be careful to stay under 1200 degrees.

Two additional techniques can help reduce cracking. After you complete the weld and while the weld is still hot, peening the welded area can help prevent cracking. This helps knock the weld into the porous areas of the casting as the weld cools. Wrapping the welded part in a thermal blanket or cooling it gradually in a pre-heated oven also helps reduce the risk of quench cracking, since these techniques allow the weld to cool more slowly.

Due to the contamination and oils that may be in a cast iron part, consider welding in very short passes. After thoroughly cleaning the material before starting, you may only be able to weld 1 inch or so in a single pass before you need to stop, brush and clean the area again. How much you must stop and start depends on how much the heat of the weld pulls contamination from the base material toward the weld puddle.


Among this list, mild steel tends to be the easiest material to weld. Engine components made from mild steel or stamped steel often include covers or brackets. While you can MIG or TIG weld these, TIG welding eliminates spatter, which can stick to the engine component and possibly break off later after reassembling the engine. A 70S-2 carbon steel TIG rod is a good option for these applications.

When working on cast steel engine repairs, you will run into the same cracking issues that can occur with cast iron. Again, the casting quality makes a difference in the ease of welding these materials.

To address the potential for cracking, follow the same procedures for preparing cast steel as you would with cast iron. Use a hot tank bath to clean the part prior to welding and be sure to thoroughly clean the welding area.

Casted parts do not like to be welded fast because it doesn’t allow the piece to transfer heat slowly. For better heat input control, use TIG welding on casted parts. A regular mild steel filler metal such as ER70S-6 or ER70S-2 works well for casted steel parts.


Magnesium is not commonly used in engine parts today, but you may run into this material when working with older parts, such as during a restoration project. This material is lightweight, very strong and less prone to cracking.

The proper technique for preparing and TIG welding magnesium is similar to TIG welding aluminum. Clean the base material well prior to welding. Keep in mind that because magnesium is not as commonly used, filler metals for this material will be more expensive.

Metal dust, grindings and shavings from magnesium are highly flammable, so keep the weld area extremely clean. Complete weld prep in an area that isn’t exposed to fire, flame or high heat.

Engine repair considerations

Whether it's an engine block or cast iron cylinder head repair, weld quality is a critical factor. Potential issues with weld cracking or poor weld quality could result in problematic and costly engine failure later.

Choosing the right filler metal for the base material you’re welding — and following some key best practices for cleaning and welding the material — can help you achieve the best results, whether you’re working with aluminum, cast iron, steel or magnesium.