Began pumping YBM.  Dewpoint of "blowdown" air comming from YBM after decoupling purge plumbing measured -16C (John elected to not repeat exercise previously done with X-end ((see recent entries))but rather to just pumpdown)*Combined Diagonal with XBM by opening GV4*Vented combined volumes*Removed all but (4) loosened bolts from BSC7 east door.  Engine hoist connected to door and taking some of the load.