96 Sonoma 4 cyl. stick, replaced head gasket. Blew the top off the spark plug. The part you bend to guage. Mechanis has no idea why. Replaced with platinum plugs same thing - all 4. No fouling… Engine, new used, still under warrantee, but mechanic doesn’t know the problem. Thanks
You may be using the wrong spark plugs. If the ground electrode is getting broken off, you may be using spark plugs with too long a reach and they are getting struck by the pistons. Is this happening to all four or just one? If it happened to just one, you may want to double check the part number, as you may have been given one wrong spark plug. If it happened to all four, I would say you definitely have the wrong spark plugs in there. You also need to pray for no engine damage due to the broken metal that is in your engine. That can easily result in severe engine damage.
Was the head machined prior to replacing the head gasket? If so, too much material may have been removed from the head where it brings the spark plugs closer to the pistons. Thereby the pistons come up and hit the spark plug ground electrode. You might check if there’s a head gasket available for head machining if it was done.