I do a lot of engine work for vintage bike owners, so I see more than my share of stripped out spark plug holes. I was working on a CB160 head today with both holes stripped out, so I thought some might like to see how I do these repairs.
Start here -
http://rides.webshots.com/photo/2993073430061780441dJYGUFView the photo and read the text, then click on "next" to the right of the photo to go to the next page. There are 14 photos in all with descriptions and explanations as clear as I could make them. I'll be glad to answer questions.
Stu