I cringed when I saw this lol.
First thing I did was try and sound out the Cyrillic text.
Then I realized there was already a translation lol
On a serious note.
I was taught many years ago when dealing with old cast iron engine parts its a good thing to try and knock off any high spots on machined surfaces with a coarse sharpening stone from the hardware store.
The process is a lot less aggressive than this and its sole function is to flatten the surfaces around nicks and marks caused by rough handling.
I can not tell you what they are saying ( I don’t speak Russian )
But I can tell you if this is indeed the master class you probably do not want them doing a valve job next.
Irmagird I was taght how to lower the head to increase hp but we had an auto mated mill that removed metal only a few thousands of an inch at a time. I suppose what they are doing would work but very hard tp get clean after