Hello. I have a '90 240 with a cross-threaded spark plug I'd like to fix. For the last two years I've been cramming the plugs into the hole as far as they will go, which is about 3/16" less than the other plugs, with no problems except a slight miss. I'd like to fix it proper with as little effort as possible. I'm thinking of rethreading the hole with the correct tap. What size is the tap? And what precautions does one need to take? Thanks.