OK, I pulled the radiator, fan, oil cooler, (I decided to change the radiator while I’m in here, BIG HOLE) valve cover, and the air cleaner. I see nothing gone too wrong except I cant turn the engine over with a socket on the crank! Even with a cheater bar! The starter will turn the engine over though, which seems really strange. What the heck could cause this? Are these engines this stiff? If I take the lower oil pan off can I see the bottom of the chain/ crank gear at all? Any Ideas what could cause this strange behavior? Tonight I plan to do some more disassembly so any tips would be great!!

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1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4