In Reply to: Exhaust manifold posted by Pete Landon on July 01, 2020 at 13:25:37:
Are you seeing fumes from the manifold? Best time to check is when it’s cold out and you can see the heat and fumes escaping. I highly doubt your manifold is warped; it most likely has worn/corroded a channel and that is where it leaks. Once worn it also destroys the gasket in that area. The 9N-9425 Manifold incorporates both the intake and the exhaust. Your intake flange has the carburetor mounted to it. The exhaust manifold will wear a channel from heat on the surface at #4 port. That is the one nearest the dash and the 90° downward pointing cast portion pipe that clamps the exhaust pipe/muffler assembly. If this is your problem, I advise to replace the manifold with a new one and don’t think about trying to ‘band-aid fix’ with multiple gaskets and/or Permatex. The job isn’t difficult, just time consuming as you need to remove a few other components in the process. You don’t want to have to do the job twice so even if your band-aid works, it would be short term so do the job right the first time and replace again a few years later when it gets worn again. If your exhaust pipe is in bad shape, you may want to replace it too at this time. Parts can be purchased at JUST8N’s –see LINK. The manifold kit includes the three gaskets –two on the engine mounting surface and one on the carb mount. You will also need to get the four 7/16-20 BRASS hex nuts with steel lockwashers, p/n 33816-KIT, that are needed to fasten the manifold with. The carb needs to come off. The air cleaner tube and rubber hose also needs to come off. There is a rubber hose and two clamps on the top of tube as well. When removing/replacing an exhaust manifold, it is a good idea to drain some coolant first. Why? Often a 7/16 stud or two will come out as you remove the old hex nuts. OEM nuts are BRASS as stated. The bottom of the radiator has a petcock on the LH side for draining. When installing the new manifold, be sure to get all the old gasket material off the block first. New manifolds usually come with the three new gaskets but there's no need to put any Permatex on when reinstalling, I don't. Two gaskets go on the block between the manifold, one on each side, not double stacked. See your manuals for your guide. Brass Hex Nuts are torqued at 27 ft/lbs. Use a new muffler clamp as well. See Bruce’s method for installing a new pipe using a block of wood and a scissor jack. The muffler clamp has large side and a small side. The large side goes on the bottom. No need to use Permatex, tin foil, or heat tape here either. See ‘75 Tips for N-Owners’ by Bruce(VA). Get new manifold and muffler connected first then install the carb and air cleaner tube.