i just built a 305 and its really strong (yes isaid 305) but my question is the #7 cylinder exhaust gasket keeps leaking ive changed the gaskets twice and i have even put 2 gaskets in there but it will start leaking after about 30 miles . any ideas of how i can make it stop leaking for good ? also i checked and the manifold was straight with no warping. thanx thomas

 

I've seen some pretty nasty looking port sealing surfaces on factory heads.

If there's enough material there, you can have them milled. Otherwise, you're looking at welding to build up the metal and then milling.

If that's your problem.

(Yes, I know 305's can feel pretty strong...)

 

Check the flange of both the header and the head; make sure the gasket actually covers them both; and that there's nothing wrong with them (especially the headers); and that the header flange mates with the head flange, i.e. that the header sealing flange isn't inside the port or outside the raised flat area of the head. Use a different gasket if the one you've been using misses the sealing surfaces. Look at your old gasket and actually figure out why it failed, and make the necessary adjustments, instead of just changing it blindly.