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.
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.