One working on an estate, say, crazy to collect heads of every Cape hyacinth (8)
I believe the answer is:
mechanic
'one working on an estate say' is the definition.
(estate is a type of car)
'crazy to collect heads of every cape hyacinth' is the wordplay.
'crazy' becomes 'manic' (I've seen this before**).
'to collect' means one lot of letters goes inside another.
'heads of' says to take the initial letters.
The first letters of 'every cape hyacinth' is 'ech'.
'manic' enclosing 'ech' is 'MECHANIC'.
(Other definitions for mechanic that I've seen before include "He services and mends cars" , "One repairs cars, say" , "One repairs machines" , "Grease-monkey" , "Worker skilled in machinery and cars" .)