When you have cracked exhaust manifold, it might be possible to repair it rather than spend money on a new one. Taking it to a repair shop could cost you quite a considerable amount for labor and parts, so trying a repair yourself first can be a good option. However, most exhaust manifolds are made from cast iron, and there are limited ways to mend such items. Follow the instructions below and see if they provide you the help you need.
Step 1 - Assess the Damage
First, remove the cracked manifold from the vehicle by removing the holding bolts from that section. Depending on the make and model of your vehicle, there will be either two or three of these. Then, take the damaged manifold off and look closely at the damage. If the crack in the manifold is narrow, as opposed to a large enough that you can get a finger inside it, it may be possible to solder it; these repairs can only be undertaken if the crack in the exhaust manifold is not too large.
Step 2 - Prepare the Crack
Scrape off any older, worn down gasket parts and clean the surface. While wearing gloves and safety glasses, bevel the crack edges to no more than 1/16 of an inch, but make sure to use a clean lint-free cloth to remove any iron filings from the inside of the manifold before you replace it back in the vehicle.
Once you have cleaned any damaged edges and removed the excess irons filings and dust, take the manifold to a worktop.
Step 3 - Solder
If you have never used a welding torch or soldering iron before, do not attempt to make this repair yourself. Set the oxy-acetylene torch to its lowest level of heat, and place the tip of the silver solder against the crack of the damaged exhaust manifold. Use a size one tip solder and place the torch very near to melt it onto and into the crack. Hold the torch evenly and use gentle strokes over the area so that you do not burn too much heat into one spot.
Continue to run the solder into the crack of the exhaust manifold until you have filled it completely. Then, use a compound like JB Weld to fill any tiny holes left over. Once the soldering has been finished, let the iron cool down naturally. Do not put it in cold water. The properties of cast iron are different to those of other metals and it will crack irreparably if you do this.
The solder solution will have a semi-permanent lifespan, but do be aware that it is strongly advised that you replace the manifold with a new or replacement part as soon as you can afford it.
Step 4 - Check for Obstructions
Once you have completed the job, check the underside or inside and make sure there are no holes or obstructions. Hopefully, having completed this, your exhaust manifold will have a solid finish and be secure enough to replace onto your vehicle.