Header gasket strength

[john.thompson068]

I will find out the answer to this by early next week anyway, but am still curious about the topic. I re-installed my left side Hooker header (next time buying TTI) after re-installing the transmission. I used a Moroso graphite header gasket. I did not tighten the bolts as tight as I normally did for fear of stripping the head bolts. So I start the motor and there is a loud exhaust leak. I cut the motor off and tighten them down some more and the leak is barely noticeable. I warm the engine up and let it cool down and re-tighten the bolts again. I did this a few times since the car was not going anywhere anytime soon and I had not tightened the bolts as tight as normal. So after all this re-tightening, they were finally really tight. As tight as I was getting them without removing the valve cover anyway. I wanted to avoid removing the valve cover because I knew as soon as I did that I would need to replace the valve cover gaskets. Since the leak was still there, just barely, I took the valve cover off (and now see the gaskets need replacing) and was able to get the bolts just a little bit tighter. Now my battery is dead and I won't get around to starting the car till next week sometime.
Here is the question. How strong are these graphite header gaskets? If I just idled the car for a few minutes with a minor but noticeable leak, and later for maybe about 30 minutes with a really small leak, and only revved the motor a few times to like 2 or 3 thousand rpm, then I would think that the gasket is still just fine and just needed to have me tighten the bolts down that tiny bit more like I did today.
These graphite gaskets seem like they would seal up real nice because they are soft and thick. However, those exhaust gasses that were leaking are pretty hot and carry a lot of energy so I wonder how destructive they would be to a layer of graphite. What does it take to blow out a header gasket, and what gaskets are most susceptible to blowing out?
I can't wait to start the car up again and hopefully it is not leaking. Last time I re-installed the header I used a similar gasket, the Napa Nitro Seal, which is no longer available, and I tightened them down like I did today with the valve covers out of the way and never had an exhaust leak until the one from this last project.

 

[ga66mopar]

Not sure if this is your problem but when I install headers on my 66 belvedere with a 440 I had the same problem. I took off the header gasket a few times and finally I noticed the heads had a casting above the center ports. This casting raised out enough to keep the header from sealing. I took off the header and used a hand grinder to ground down the casting. Solved my problem. I used the felpro header gasket with high temp lock washers. Not had anymore header problems.

 

[70redbee]

I have had that problem before and only fixed it by putting 2 felpro header gaskets on. Maybe try this, don't know if it will fix your problem but worth a try.

 

[john.thompson068]

I said Moroso gaskets but that is a wrong. They are the Fel Pro gaskets. The heads are Edelbrock RPM so no clearance issues. If it still leaks I will replace the gasket with my extra one and this time remove the valve covers and tighten them down really tight before letting any gasses have a chance to possibly burn a groove in the gasket. I can't imagine this being the case in this situation since the motor has pretty much just been idling in my garage.

 

[1toolguy]

Next time try Remflex header gaskets, they're a bit more expensive than the rest but thicker and a bit more compressable so they fill in all those little imperfections that cause leaks. I installed a set 2 years ago, never retightened them and they have not leaked once.

 

[quick63]

use "dead soft" aluminum header gaskets from Mr. Gasket and install studs. No more header leaks.