This followed the two changes yesterday, when new turbocghargers and MGU-Hs meant a 30-placev grid drop.
This morning's change, which included a sixth internal combustion engine (ICE), sixth MGU-K, eighth MGU-H and an eighth turbocharger, means a further 25-place drop.
"Straight into race sim work for Lewis with practice starts and cruise laps," tweeted Mercedes earlier as the Briton finally emerged from his garage. "No need for blistering times today. When you're starting from the back, it's all about race pace."
That said, in the final moments of the session, having struggled with his tyres, the world champion banged in a 1:48.635 which put him fifth on the timesheets, two places ahead of his teammte.
In view of the grid penalties, and with an eye on saving tyres, it is unlikely that Hamilton will do much running in qualifying this afternoon.
Check out our Saturday gallery from Spa, here.