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.
Re: does gas eat through super glue? (civicdxtyper). JB weld takes around 8 hours to cure. Try plastic welding it with a soldering iron first by just melting the plastic together with the tip (I have never heard of a brand of plastic weld?) then use jb weld on top as a double dose for increased strength.