Re: Any explanation for this????
First understand that the same gasket is used for the small bore 3.3125 engines and the big bore 3.375 engines and is slightly larger in inside diameter than the big bore size. The steel sealing ring is "U" shaped in cross section and is supported by the fiber portion of the head gasket--(actually fiber over steel in some cases--depends upon the manufacturer).
Your engine is small bore.
Production tolerances allow the gasket to seat not perfectly centered on the block and head mating surfaces. This coupled with gasket aging allowing improper support of the steel ring or slight corrosion on the metal the ring is compressed against, or incorrect head bolt torque, or overheating will allow combustion pressure to either leak past the sealing ring eventually destroying it and the gasket support inside it, or blow by and quickly totally destroy the ring at that point.
Either way, one cylinder will lose compression while not suffering any damage.
When you replace the gasket, torque in three stages to 225 INCH pounds. After running the engine for about 1/2 hour (or more) let cool and re-torque to 225. Yes, many times the gasket will compress a little under heat and need the re-torque. Old re-used gaskets are fully compressed and usually don't need re-torquing.
