The saw seems to only emit smoke in selected scenes; I didn't pay attention whether the chain itself is spinning in a recent screening (the 50th anniversary 4K restoration).
Roger Ebert notes in his review of the 1986 sequel:
One technical point: The chainsaws are not actually turned on during most of the big scenes. Well, how could they be? You can see they’re not moving, even though you hear them on the sound track.
by garden-3750
4 Comments
I assumed the chainsaw was running but the chain itself had been removed.
Not sure about the whole movie, but there are scenes where an intact chainsaw is running dangerously close to people, yeah. Some of the cast really did not feel like Tobe Hooper respected their safety IIRC
it’s a low budget film with a new director in early-mid 70’s
my guess is yes the chainsaw was running at some points
You can remove the chain from a chainsaw. So you can have it running, but completely safe.