head warp around exhaust studs

[Counter]

All - '81 850GX. I took off the headers, cleaned them up (steel wool and deep creep) and tried to put them back on. I broke one bolt off in the head.
The funny thing is that the bolt broke and I wasn't pulling any harder on it than for the previous 3 or 4 revolutions.

Anyway, I decided to buy a tap and die set and go over the bolts and the bolt holes so I could get a clean reading on my torque wrench. The bolts went OK, but the holes were terrible. I thought the tap was going to break while cleaning up a couple of the threads. It literally took me about 45 minutes to clean up the already existing holes. Any thoughts on why the holes were so bad?

[bietau85]

30 years of corrosion and variable hot as hell heat? just a thought. lol

[sachsaca]

30 years of corrosion and variable hot a hell heat? just a thought. lol

Yea, what he said

[Counter]

I was worried about the head warping. I was told by an old mechanic (car, not motorcycle) that tapping the head was a bad idea since it could enlarge the holes and make the bolts not hold as well.

I did it anyway, because that's what i do...

BTW, when the head of the bolt broke off, I used an ez-out that dug into the drilled hole when turning the bolt out. It worked, but I did it carefully.

[Agemax]

you cant enlarge the threads by tapping them out, unless you use the wrong size tap!

[Nessism]

Tapping the holes is risky because it's really easy to get the tap started crooked, also, ideally you should use an undersized tap since this takes out less material. Engine rebuilders often use these undersized taps for just such reasons as your mechanic states.