Me and another member here on the forums are having some smoking on startup problems after we both have done fresh head jobs on our trucks. I've been pointed in the direction of piston rings and bad valve guides.

My question is, what happens when a valve guide goes bad? I found some for a decent price and I want to know how they go bad, and is it worth the extra month to get the higher quality parts when it comes to valve guides.

Also, this is a secondary question. How hard are they to replace? Is it a DIY job? I did the head job myself and I'm certain I can get the head off in a day and get it back together the next. Do I need any special tools for this?