In reply to a message from blatch sent Mon 25 Apr 2005:
If there is a few millimetres of bolt left above the surface you
may be able to grind a screw slot in the top and turn with a screw
If they have sheared flush, or even below the surface then you will
need to try ‘thread extractors’. These look like a tapered screw
with a reverse thread ( I think they may be called Eazy-outs in the
USA? Or is that a brand name? )
You need to drill a hole of the correct diameter to use one
successfully, and this is important. Also, centre punch the stub so
that you start drilling in the right place, then drill a smaller
diameter pilot hole no more than say 1/16th first.
Use plenty of oil on the drill bits too - engine oil will do. If
necessary have an assistant run oil on the drilling site.
Equally important is to drill squarely into the broken stub,
otherwise turning the thread extractor will tend to put sideways
forces on it. This could break one.
One variation on this technique that I’ve seen recently, is
a ‘drill bit’ with a reverse spiral cut, and intended to turn in
the opposite direction. The theory is that sometimes, just the
drilling will apply enough torque to turn the stub out. The key is
to use a slow drill speed. If this doesn’t work then you are simply
left with a hole that can be used for a thread extractor.
If this fails too or the extractor breaks then you would have to
drill the stub out, and re-tap the thread. The most difficult part
will be guiding the drill squarely so that it doesn’t wander off
sideways into the casting. I’ve had get a broken stud out of a
cylinder head before now, and welded a guide ‘rig’ together from
scrap steel, to support the tip of a drill bit. It used adjacent
studs in the cylinder head for support.
You may also need a ‘90 degree head’ drill just to be able to get
any sort of drill bit to the stubs at all. In the UK at least,
these can be hired.
Finally, spray them well with penetrating oil a day or two before
you start, if possible.
The original message included these comments:
Can anyone enlighten me as to how one removes ‘‘sheared bolts’’?
Fortunately this is not on my Jag, but on another car that I have.
When removing the water pump, the bolts were so old two of them
sheared. Any explanation on drilling and tapping, or any other
tricks to fet them out will be greatly appreciated. Thanx in
Andy Blakey 1983 XJ6 III 4.2 Auto (UK) '‘Jane Seymour’
London, United Kingdom
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