Should you replace timing chain, guides and tensioners?
 

I have a 2005 Mercury Mariner/Escape with 220 K Miles

Lately I have been scared about timing chain and guides wearing off in engines. I have always been told that timing chain can last the life of the enginehttp://images.intellitxt.com/ast/adTypes/icon1.png but I am worried when should we replace guides and tensioners as they are mostly made of plastic.

I dont' see those in recommended service in the books as I see timing belts. I have driven my other cars with timing chaines almost 230 K miles without any problem.

What are you thoughts on this? Should you only do it if the plastic guides break?