Darn, you just beat me to it...
Seen this happen before with easyouts and drillbits broken off...
Punch and drill round the broken bit, and (as you found), the tapped hole is either recoverable or helicoidable
Well done!
Cordialement,
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skippymoss wrote: one of the studs on number 3 cylinder broke off flush with the head - I sent it to the local engineering place for a helicoil