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.
How it's done: 1  Determine if the manifold is cracked or broken. 2  Remove and replace faulty exhaust manifold. 3  Inspect exhaust studs, clean carbon and old gasket off cylinder head.  Install new gasket and exhaust 1  manifold. Start engine and check for exhaust leaks.