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Head Gasket Failure
Somewhere recently I read that a possible cause of a head gasket failing between 2 and 3 could be caused by over-advanced ignition timing. Could anyone explain the theory behind this?
Many textbooks publish graphs of the pressure in a cylinder. With advanced spark the peak pressure increases dramatically; out of all proportion to any slight power gain. (Somewhat  the same applies to c.r. increase. both excessive advance and raised cr are hard on poorly supported cranks. No more advance than necessary for full power should be used, and often a little less is prudent) ) If the engine actually pings pressure waves sufficent to make the metal ring as if struck by a hammer occur. So excess advance does increase the risk but any head gasket in any car should withstand. 
There seems to be some doubt about the properties of modern asbestos free gasket materials. I wonder if excessive tightening as often advocated crushes all the resilience out of the gasket. Years ago it was normal to repeatedly reuse gaskets. I always did so on the Seven and makes I operated and never had one blow (although few came off without staining in parts).
That's a new one on me. If the ignition is too far advanced peak cylinder pressure occurs before TDC then there's an almighty stress put on the gasket as well as everything else in the engine. Far more likely though the 'bridge' between the cylinders is corroded, overheating has occurred, or the joint face is not flat, in my 'umble opinion.
Probably a combination of the two; if the joint is already weakened by corrosion or less-than-perfect sealing, then the added loads created by over-advancing become the final straw.
Or a block crack between 2 and 3 across stud hole, then leaves a potentially loosened stud that leaves the area more likely to suffer a blown gasket?
Enjoy yourself, it's later than you think!
Thanks all. I think it might be prudent to put a new block on the shopping list - looking at worst case scenario.
It's nice to have a spare. It may respond to a light skim though if flatness is the issue. Absolute minimum of material off though or you may cause other problems. Consensus here I think is that cracks around the centre stud are generally tolerable if the rest of the block is sound - perhaps not on a performance car.

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