Exhaust keeps burning throug header gasket

[DatsunZman04]

I have a 72 Datsun 240 z with a 240 block and head. I am still using the stock cast header that came on the car.

 

My porblem is the gasket between the exhaust pipe and the lower part of the header keeps blowing out. I have tried a new gasket, with High temp rtv silicone, I have also tried making my own using gasket material, I have also tried taking some old small donut gaskits and tried that but still blows out after a week or so. I have taken the header off and made sure it wasn't warped or had any left over resdue from previous gaskets/ silicone. I need to buy a 6 to 1 header but my money is going to my v8 project and dont want to spend it on that if not going to be used. I am scared to over tighten the studs on the manifold for fear of twisting them off. Then I will have some serious problems. As far as I can tell it sits and mounts up flush but that wouldnt explain the blow outs.

 

Has anyone else have had similar problems? I am just looking for some advice or a decent direction to be pointed in.

 

Thanks again Datsunzman04

[BluDestiny]

Blue stag had this exact problem a few months back. Search for it. There were a lot of good ideas in that thread.

[Pharaohabq]

Sounds to me like it's not actually as flush as you think. is it possible there's some bowing going on between the bolts? Do you have any pictures of the damage?

[evildky]

I had this problem years back, I had the head surfaced ont eh gasket side at a machine shop as well as my exhaust manifold, never had another problem