Remove Exhaust manifold as described in the R33 Workshop Manual on pages  135 / 6.  The inboard water cooling banjo connection  on the turbo is 24mm  and was very difficult to access and extremely tight.

Using ‘freeze and release’ undo as many manifold nuts as possible.  I managed to get off  seven , the remaining five were broken just below the surface of the head ( the front three and the rear two ).   Spray the remaining good studs with ‘freeze and release’ and using the 10mm stud remover remove the studs.

The first thing  to do was to centre punch the centre of the broken stud.  To assist the centring I made an aid from acrylic for the automatic centre punch  .  These studs are made from  a very hard steel and took the point off of the centre punch - it required re-grinding twice.  It is essential to get this bit right  - I would suggest checking and re-checking the centre punch mark is central on the broken stud.  I reinforced the automatic punch mark by using a traditional centre punch and hammer.  The most difficult one to do is the rear one.  With the studs punched it is now possible to start drilling.   

Drilling

I used cobalt drills and used a new one every two studs.  I started by drilling with a 2mm drill driven from a right angle drill attachment attached to a reversible variable speed battery powered drill fitted with a torque clutch drive.  I drilled in to the stud approximately 2 - 3mm then changed to a 3mm cobalt drill and continued drilling.  It was possible to check the centre accuracy  of the drilling by using a mirror and a torch to illuminate the area.  In my case one side effect of changing from the 2mm drill to a 3mm drill was to loosen the stud and drive it  further in to the head.  At this stage I would suggest using a small rotary brass wire brush to clean the top of the thread as it is most likely contaminated with exhaust carbon which will make it harder to extract.  The stud can be driven to the top of the thread by using the left twist drills - do not forget to reverse the direction of the drill when using these drills .  The left twist drills were only HSS and became dull very quickly but they did force the stud to the top of the thread where it stayed and allowed completion of the drilling to a depth of  approximately 6 - 7 mm by using the 3mm cobalt drill.   This depth was required to ensure that the cobalt easy out did not bottom out on the hole as it was turned.  I drilled and removed the broken studs one at a time.