i have a '94 4.3 blazer,,fixing head gaskets now,,,i bought it and drove it home it ran fine,, took it out later that day andit started spark knocking really bad,i tried messing with the timing and i couldnt get it to stop, even under the littlest of a load....now it has a blown head gasket...my question is,,what made it start spark knocking like crazy? could that have been the head gasket gowing? i know the spark knocking could eat at the gasket...but i want to know if it was cause or effect to the head gasket,,and what could be the cure....help !!

 

How did the combustion chambers look inside once you got the heads off? Carbon buildup can cause hot spots which will intern cause preignition.