Hillsborough County schools get out May 25 for the summer break. ChaCha on! 7 years ago
Â· just now. Report Abuse. A cast iron manifold will expand and contract, the JB Weld will not. I think JB Weld is fantastic stuff (have some as we speak) but not for a cracked exhaust manifold.You can always check out their website: http://jbweld.net/index.php I only have experienced JB with cast though, if your manifold is another material you may get lucky.ource(s): Q: Will J-B Weld work on an automotive exhaust? A: Because of the extreme temperatures of exhaust systems, we do not recommend J-B Weld for use on exhaust manifolds and catalytic converters.
Remove the exhaust manifold from the vehicle. Welding the manifold while it is still on the engine is very dangerous because flammable chemicals are everywhere. Depending on the year, make and model of the vehicle, the removal task can take anywhere from ten minutes to an hour or more.eld the crack. Because the metal of exhaust manifolds is normally very thick, you can turn your welder's power up almost all the way, especially if the machine runs on 110 volt house current.