It take a different bit to clean up threads, taps are for cutting not cleaning. Here is the bit for chasing the threads. I know it is to late for future reference it is a good thing to know.

ARP 911-0002, ARP Thread Cleaning Chasers | ARP
"Note: These are strictly cleaning taps and are NOT designed to cut thread."

Glad all turned out well and lucky it broke off close to the surface...