[s-cars] For your debating pleasure (headgaskets)

Cody Forbes cody at 5000tq.com
Tue May 1 01:20:53 EDT 2007

A month or so ago I was inquiring about using the all metal updated AAN/3B head gasket on an MC engine. Well last week I blew my head gasket (due to some detonation), and spent some time trying to decide which to go with. In the end I used the metal gasket. S-car content is scarce since you guys should all be using the metal gasket anyways, so feel free to use your delete key throughout the ensuing thread S-heads ;-).

http://jcforbes.com/jcfpics/headgaskets - A bunch of photos of a stock MC gasket, a stock 3B gasket, and the all metal AAN/3B gasket.

You'll notice that the metal 20vT gasket is actually closer to the MC gasket in terms of water passages then it is to the stock 20vT gasket. I thought that was fairly interesting. The coolant ports were slightly different, and yes especially so arround cylinder #5, but I do believe I made the right choice. Not pictured is a brand new MC gasket I compared to my blown MC gasket just to check for any damage outside of the obvious. I found that on both my old gasket and the new MC gasket that the bore was 82.5mm at the smallest dimension (odd considering the cyl bore is 81mm), but also that they were very very oval shaped - in the order of a 3-4mm difference between their smallest and largest dimensions.

http://jcforbes.com/jcfpics/headgaskets/P1010044 - Bad photo I know, but you can clearly see that the metal gasket (lain underneath the MC gasket) has a proper 81mm bore, and it illustrates exactly how ovaled the MC gasket was. This ovaling was *NOT* damage, the new MC gasket was absolutely identical when measured with calipers. This ovaling is what caused the failure in my case, as my block has steel o-rings to prevent such failures, but the oval gasket actually missed the bottom portion of the o-ring from about 4:30 to 7:30.

Anyways, theres some food for thought, enjoy. 

-Cody Forbes

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