Im not a big fan of chasing threads in aluminum, especially with a cutting tap (big no-no). You could try it but it might make the thread engagement lose and cause more problems later. Time-sert, Keensert or Helicoil thread repair would be the preference, in that order.
JMO but I don't believe part of the thread would cause that type of damage as the thread is the same type of material as the piston and cylinder. Wht ever did that was harder than these two. It could be a piece of cage material from a bearing or other foreign particle.