Header stud threads

[Mval75]

While removing my old broken and leaky exhaust I broke off a stud in the block. I was able to remove it relatively easy, but messed up threads on other studs and just decided to replace all studs with new while I had the exhaust off. None of them came out very easily. New studs came in yesterday and I've got all but one in, I could not get this one to start. Is there any way to clean up the threads in the head without causing more damage? If not what is the best method for repair? Thanks

[Harryc]

The only method to clean up threads that I am aware of is to use a tap, but it depends on what you mean by 'damage'. Are the threads completely stripped out? partially? If there's no threads left you'll need to use a helicoil or drill and tap to the next size stud up.

[bentwrench]

Helicoils  can restore threads the same size as oem 8mmx1.25 pitch is the size helicoil you need(I think).
A thread chaser from a tool supply can restore threads that aren't too badly damaged.Taps are very sharp and can sometimes remove too much metal when used as a chaser.
A "little" heat and some pb blaster helps getting the old ones out without damage too.

[Mval75]

Yeah sorry, by damaged I mean 1/4 of the way in looks to have been cross threaded or over torqued. The rest of the threads appear from what I can see to be fine.

[WintrSol]

Instead of a tap, they make things called 'thread chasers', which are designed to clean up threads, not cut new ones. It's very hard to find them that small, but they do exist (I have a set). But, from your description of the damage, a thread chaser may not work well enough, in which case the thread insert (HeliCoil) would be the way. The trick is to get a really straight shot with the drill, then use cutting oil or compound when cutting the threads for the insert.

[Hooter]

Try a bottoming tap. If that doesn't work then like someone said helicoil.