If enough oil was lost to cause a knock, it had to be more than 2.5 quarts. Where did the oil run out? What bolt came out? If the bolt went into the oil gallery it could have been running on low oil pressure even if there was oil in the system.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13