A question about "bicycle" and "motorcycle"?

[Queen Kira]

Why do we say "bi-sickle", but we say "motor-sykle"?

(I've heard a few people say "motor-sickle", but it's very rare).

 

[Diet Pepsi Max Fan]

Because of the stress pattern.

In bicycle, there is one stress on the first syllable.
In motorcycle, the 3rd syllable receives secondary stress, with allows for a diphthong (a-y) in that position.