my son was changing his spark plugs and broke the top half of the spark plug off, with the bottom still inside the engine block. How can I get the broken bottom part out of the engine?
Go back in with the correct spark plug socket. Sometimes packing a little tape in the socket sticky side out can help grasp the remaining part. Usually it comes right out, unless there is a seizing problem. If the socket doesn’t get it out cleanly, then take long tweezers or tongs if needed to get the remaining piece out.
Spark plugs don’t go in the block, they go in the cylinder head. If he broke the ceramic off, the part the socket fits on is still there. Get a flashlight and look. Or tell him to get a flashlight and look. It’s pretty hard to break the metal part of the plug.
If this is the first time the plugs have been changed, soaking them with penetrating oil might help. Make sure he puts anti-seize on the threads before installing the new plugs.