Removing the ‑EN ending from the infinitive does not change the sound of the remaining verb stem, but often the spelling changes.
In the three examples above, the spelling doesn't change because there are two or more different consonants before the ‑EN ending, but with one consonant or two of the same consonants before the ‑EN ending there will be spelling changes

• verb infinitive:	... single vowel	—	single consonant	—	‑EN
  verb stem:	... double vowel	—	single consonant

       halen 2 'to get, collect'   haal
       nemen 'to take'   neem
       lopen 2 'to walk'   loop 2
  A single vowel followed by a single consonant before the ‑EN ending will become a double vowel when the ‑EN ending is removed, because a single vowel before a single consonant that is the end of the word is 'short.' The vowel is doubled to indicate that it's 'long'

• verb infinitive:	... single vowel	—	double consonant	—	‑ EN
  verb stem:	... single vowel	—	single consonant

       vallen 'to fall'   val
       zeggen 2 3 'to say'   zeg 2 3
       willen 2 'to want, wish, desire'   wil
  A double consonant before the ‑EN ending will become a single consonant when the ‑EN ending is removed because Dutch words don't end in double consonants.
  A single vowel before single consonant at the end of a word  is short; a double consonant in the middle of a word indicates that a single vowel before it is 'short'