Lower TC guides question
 

I am about to change the upper guides and tc chain on my 420. How important is it to change the bottom? Car is an 87 with 80k on odometer...

The upper rails should be replaced every 75k or five years. The lower passenger side rail is the only rail of importance in the lower timing cover and it lasts between 3-400,000 miles. The tentioning rail which is also on that side can be easily replaced without removing the front cover and is should be replaced if deeply grooved.