I have an L28 from a 280zx in my 240. I have a fat exhaust leak right where my header connects to my head.
-Can someone explain to me how this can burn valves?

-Also, when replacing an exhaust/intake manifold gasket, what is the best kind of gasket and sealant to use?

-Last, how can I tell if my header is aligned correctly? I have a lot of free play as far as up and down and last time I succeded in making my leak bigger by misaligning.

Any suggested methods to go about doing this? My head was shimmed and shaved and it slightly changed the angle of the head meaning the header is not at the right angle. Last time I just used force to move the header up a little on one side(not good for the rest of my exhaust) Should I cut the header away from exhaust and then reweld or...?

 

I don't see how shaving the head would make it sit at a different angle?? It wouldn't, it would just slightly lower but not enough to make any difference at all, its in your head. Anyhow, I suggest you buy a stud kit from MSA. Remove your intake manifold and pull your exhaust manifold off. Remove the old studs, thread in the new ones-get an exhaust manifold gasket that crushes when your torque it on, it really helps it seal alot better from my experience. Don't use any sealant at all, it'll just burn off and smoke alot. I would suggest cutting the header away from the pipe to allow yourself free play as necessary. Line it up as best as you can, torque the header on nice and tighten but don't overtighten, then get your pipe welded back up and that should do it.

 

It can burn valves because the air flow is venting to close to your valve which can cause it to burn. It is more technical than that but that is that strppied down version. I know I had a leak in my chevy truck and I sucked 2 valves not a pretty sight. It screwed up my pistons and my block was junk. So if i was you I would get the gasket kit from MSA and do the change your thank yourself later.

Gotta get my Z's