Tap n' Die Questions - longish

[tberk@mindspring.com (T Berk)]

(btw- pls edit out the top text when replying to this, I think the
Digest folks will certainly appreciate it.)

I picked up a Hydro GTI head some time back, had the mating surface
flattened and found some time in it's past it had (at least once
before been a replacement. 

Trouble was it had an exhaust stud broken off just beneath flush and I
wanted to get the old steel out of the aluminum head before putting my
motor back together.

I have had poor success (if you can call it that) with those reverse
thread screw extractor, after all the two different metals have galled
to each other, what with the heat and all, it's better I think to just
drill it out and re-thread.

A friend loaned me a Helicoil tap but I realize it doesn't leave
thread ready for the stud, and I'd rather tap directly, besides I have
no coils at the moment anyway.

Lucky for me I was able to locate an ala carte M8x1.25 metric tap
today at Orchard Supply.  :])

So, I know you probably want to go over the basics with me (if you
would) and fill n the glaring blanks in my knowledge.

- You want to go slow, maybe advancing only 1/4 turn each time. 

- You want to use some lubricating oil, somewhat like cutting oil.

- You want to drill the pilot hole to xxxxx size for a metric 8 by
1.25 hole.


Thx and Keep a Rocc'n.
TBerk
Getting back to life, without Meds.