Some more information about the altering of the conventional forms and pronunciation of the word "ache" is found in the etymology of the verb. Dr Johnson seems not to have been quite the infallible sage some think him to be.
[Originally a strong vb. of same class as take, shake, but with weak inflections since 4. The current spelling ache is erroneous; the vb. being historically ake, and the n. ache, as in bake, batch, speak, speech. About 1700 the n. began to be confused in pronunciation with the vb., whence some confusion in spelling between ache and ake; and finally instead of both being written ake—the word that has survived,—both vb. and n. are now written ache—the word that has become obsolete. That is, the word ache has become obs. and been replaced by the word ake, while the spelling ake has become obs. and been replaced by the spelling ache. For this paradoxical result, Dr. Johnson is mainly responsible: ignorant of the history of the words, and erroneously deriving them from the Gr. **** (with which they have no connexion) he declared them ‘more grammatically written ache.’ See next word.]