PEH, I don't have that particular eng. mine is a 617.950. What I do know is that usually what car companies do to get away from valve adjustment requirements, they install hyd. lifters. This is what Porsche recently did. So maybe that is what MB did. As far as the aluminum head/iron block issue. I too was wondering how they do it. I had a 1985 Ford Escort with a iron block/alum. head. I also had a Ford Taurus 3.8 V6 with the same arrangement. My Vw Passat 1.8, 4cyl, 20 valve head is the same way iron/alum. So companies have been doing it for years. This type of arrangement is probably the reason the cooling system is real critical these days.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member