Is your question about the timing chain in relation to removal of the vacuum pump? If so, the vacuum pump is not driven directly by the chain. There is a disk in the engine under the pump that is rotated by the timing chain. The disk contacts the vacuum pump push rod and creates the pumping motion. Bottom line is the timing chain is still engaged with the vacuum pump disk even after the pump is removed.

Good luck!

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold