Scam involved Henry and back part of engine (8)
I believe the answer is:
camshaft
'part of engine' is the definition.
('camshaft' is part of 'engine')
'scam involved henry and back' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'and' says to put letters next to each other.
'back' becomes 'aft' (associated in meaning).
'scam' is an anagram of 'cams'.
'cams'+'h'+'aft'='CAMSHAFT'
(Other definitions for camshaft that I've seen before include "Rod to operate valves in an engine" , "It operates the valves of an internal-combustion engine" , "Car part" , "Fat chasm (anag) - internal-combustion engine part" , "What imparts motion to engine's valves" .)