[alfa] Cam bearing stud pulling out, drilling holes in heads

[Jon Pike <jhpike@xxxxxxx>]

Hi All..

Well, the second cam bearing stud pulled up on the head,  as I did my 
final pull 'em up, take off the sprocket nuts to put fresh locktabs on 
and tighten them back down.

I use a checked torque wrench,  at 15 ft lbs,  oiled threads and nuts, 
set the cams to a place where there was two valves nearly closed, loosen 
and tighten the nuts slowly and evenly.. but it happened anyway.

This time,  I did something dumb, I put the bearing caps on backward, 
(correct bearing cap for position, but turned around on its spot)   and 
didn't notice till I'd torqued them down.  I did notice when it was more 
difficult to turn the cam with the cam tool.  So, this might have put 
some side force on the studs,  and hopefully not too much on the bearing 
surfaces.

But the other time,  as far as I could tell,  I did nothing unusual. 
Why does this happen?  Just age,  is there a techniqe I'm not aware of, 
or what?  I really don't want to have this happen again..  though I see 
a few studs "taller" than the others, and might end up here again.  I 
have had thoughts of playing with the cam timing,  or putting on a set 
of Euro cams in the future,  but if the bearing studs are this fragile, 
I better not. 
So, am I doing anything wrong?

Secondary question..  How deep can one safely drill into a head,  for a 
thread repair insert?  I have a Timesert kit on the way,  and know that 
any tap has some starting taper,  so in a blind hole you have to 
overdrill somewhat.  This is where I wish the engineering drawings were 
available, so I could tell how much aluminum, and what else,  is under 
there.  I surely dont' want to drill into a water passage or worse!  I 
have one in the head already,  so I assume it's OK,  but it would be 
nice to know how much of a safety buffer I have.

The Timesert guys are gone for Xmas,  so I don't know how much overdrill 
is neccicary for their taps. I of course want to drill just enough...

Jon
77 Spider
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