Our 300sdl has 227k on it and I am going to replace the timing chain. I want to know.....

1. Do you have to tear apart the whole front end to replace the guide rails?

2. How long do the rails usually last?

3. Can I just replace the timing chain and forget about the rails?

4. Is there a way to inspect the rails or do you just automaticly replace them?

Thank You very much!

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87' 300sdl

The rails can last longer than the miles you have now. That being said they are not THAT hard to replace, and are usually not THAT expensive. Some members here have reported they lost their engines from a failed cam chain slide. As best I can recall it is reported they can come apart in there and wreck your whole day.
To check the wear on them you should be able to loosen the cam chain tightener and get a reasonable view of most of the slide. It will show some wear marks from the chain, a judgement call as to the extent.
I replaced them all on my 300SD with 215,000 miles. On that engine the banana slide, that is shoved by the tensioner into the chain, is removed by pulling the pin down near the bottom of the rail. A stacked nut or socket is placed over the pin, and a bolt goes into the center of the pin and is pulled out with the bolt. On that engine the most I had to do was to remove the front pulley and the small plate over the front seal. I don't know about the SDL engine. The rest are mounted much the same, and are not any more difficult to pull, with the exception of the lower slide. I was told to forget about getting to that one.

I just checked the banana shaped guide and it looks like the deepest groove is about .030". I guess it didn't look that bad to me.

One thing I did see that was interesting is that it looks like oil pressure is used to push out the inside of the tensioner to assist the spring.

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87' 300sdl