The most common and most likely answer to this crossword clue is the 10 letter word TWO-STROKE
I've seen this crossword clue in The Guardian
T
W
O
-
S
T
R
O
K
E
Buddy explains!
The straight part
We know that "Motor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case motor = two-stroke.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 TWO-STROKE mean?
TWO-STROKE noun- As a determiner, of a type of internal combustion engine, the working cycle of which is completed during two strokes of the piston.
- The fuel used in a two-stroke engine.
- Coca-Cola