A question concerning the replacement of the chain guide rails - can this job be done with the head on the car, or is it required to remove the head to get the main rail and the lower guide out? What about the intermediate rail below in the intake camshaft sprocket?

We have a unit that is eating these items. It ate the guide below the intake camshaft sprocket about two years ago and that caused all kinds of problems with oil pressure. We removed the remnants from the oil pan and the oil pump suction strainer and things returned pretty close to normal. It seems at about the same time we have developed a means for gasoline to mix with the engine oil which also adversely affects the idle oil pressure and the characteristics of the oil, so this car gets lots of oil changes while we try to figure that item out.

Today we noticed some rattling noises from the front of the engine and took the valve cover off, only to notice the main tensioning rail (on the exhaust camshaft side of the engine and it is the rail in contact with the chain tensioner) was worn away to the point where the sides of the rail protrude past the chain at the top of the rail. The chain is still reasonably tight but it would seem this item is due for replacement.

So, can this job be done without removing the head? While we are in there we would also like to replace the oil pump.

Any input would be welcome. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)