Timming chain rails:4 or 6
 

When a local indy replaced the timming chain and rails, they only replaced the 4 top rails. My cd shows 2 more on the bottom, should they also be replaced at the same time?

I wouldn't be concerned. The most important thing is that they replaced the chain. I just picked up a nice 91 420SEL for a song that I'll fix and probably give to my youngest daughter. It has the classic bent valves on the left bank. The rail in that head broke, but only because it got the crap beat out of it by an elongated chain.

Peter

Should the two bottom rails ever be replaced?

They usually get grooved pretty well which in most peoples opinion does not affect the chain tension much or more importantly do they have the risk of self-destructing like the upper rails. I did the lowers on my 420 at 125K because I ended up pulling the engine to reseal the heads.

It is quite a bit of extra work to change them, I wouldn't worry about it too much.

Read Steve's comments on this here:

http://www.peachparts.com/shopforum/showthread.php?threadid=87412&highlight=timing