<VV> Re/ Pulled head stud/block repair

[Jim Simpson]

I had a similar problem with a pulled head stud.  The problem with helicoils
is that the commonly available ones are short (not the full length of the
threads in the block) and you need all the holding power you can get.  You
can get longer helicoils, but if the hole has been enlarged beyond the "step
up" size of the helicoil, you have three approaches.

One is to replace the block.  But if it is in good condition otherwise, I'd
try a repair.

There are two repair options as others have pointed out.  One is to have
someone weld the hole up and then redrill and retap the hole.  That would be
the most "professional" route.  The other -- which I used -- was to make an
insert.  Tap new threads into the existing hole sized to fit a larger bolt.
That is, find a bolt that can be threaded into new threads cut into the
existing hole.  Center drill and tap the bolt to fit a new head stud.  Cut
it to length to match the thickness of the crankcase -- ideally it will be
flush with the outside of the crankcase when you're done.  You'll insert the
bolt from the INSIDE of the crankcase; but before you do, measure the
clearance between the crankshaft and the inside of the crankcase.  You'll
almost certainly have to grind the top of the bolt down to ensure there's
enough clearance.

As long as there's enough of the hex head of the bolt left to give a wrench
something to hang onto, you're fine.  Put a sealant of some kind -- I'd use
Locktite to make it permanent -- and screw the bolt in and snug it down.  It
doesn't have to be overly tight -- the remnants of the hex head will keep it
from pulling through.  Once the Locktite is set, screw in the new head stud
(again with some sealant).  I don't think that stud will ever pull out
again!

Jim Simpson
Group Corvair