The most common and most likely answer to this crossword clue is the 8 letter word CAMSHAFT
I've seen this crossword clue in The Daily Telegraph
C
A
M
S
H
A
F
T
More clues leading to the result CAMSHAFT
- In the morning, mum in fact damaged part of engine
- Part of engineās mass in fact has broken
- Male introduced to change rear part of motor
- Minutes consumed by change to the rear part of engine
- Half of safety match replaced part of an engine
- Get a handle on computer-aided manufacturing for car part
- Machine part chap must regularly handle
- Scotsman returns with rod for engine component
- Part of engine's mass in fact has broken
- Mum invested in banker behind revolutionary engine part
Buddy explains!

The straight part
We know that "Machine part" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case machine part = camshaft.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CAMSHAFT mean?
CAMSHAFT noun- A shaft fitted with cams; especially one in a piston engine that activates the valves.