G’day to All Those Who’ve Managed to Snap a Head Stud or Two,
I recently had to remove the head from my son’s car, a SIII XJ6, due to
constant coolant loss between the head and the block. The head came off
fairly easily but it was obvious that the car had been run without the
correct coolant for some time. The water galleries were gunked up with scale
and rust flakes and the head gasket was actually installed upside down,
which wouldn’t have helped much. Anyhow I decided to remove the head studs
to check on their condition and managed to snap one off at the base. It
broke right where the thread started, about four turns out of the base of
the block. Examining the fracture plane revealed that the stud was cracked
around 2/3rds through, maybe torqued up too much when installed by the PO.
I removed the core plug to get access but couldn’t move the stud with vice
grips or heat etc so the options were to short stud the block or try and
drill out the stud remains and heli-coil the hole and use a normal long
stud. I spoke to the local supplier about the problem and he said that quite
a lot of local competition drivers use heli-coils for a lot of different
applications. He couldn’t see it being too much of a problem.
So I bought the right sized kit, actually made in Australia by a company
called Recoil, www.recoil.com.au and two extended length drills, one to
drill a pilot hole and the other to drill out the stud remains. The Recoil
kit thread tap is far too short to reach deep into the block as is the coil
inserting tool so I had them both extended to a suitable length, the same as
one of the studs, by an engineering workshop.
Now for the acid test, will it all work? I started by grinding the top of
the stud remains until it was clean and flat, and then used one of the old
studs ground to a point as a centre punch to mark the centre for the pilot
hole. Then I very carefully started to drill the pilot hole, at first
turning the drill chuck by hand until it bit into the metal a little, then
at a slow speed using the electric drill. Used plenty of lubricating oil and
removed the drill several times to clean out the swarf. I had previously
marked the drill with a paint stripe, using an adjacent hole as a depth
gauge, so I didn’t keep drilling into the sump. Once that hole was done I
then used the larger drill to drill out the stud so I could then use the
extended tap to prepare the hole for the coil insertion. Once again slowly
and carefully. The only thing that gave me cause for concern was when the
large drill stopped drilling with about a quarter inch to go. Hmmm, I
retracted the drill and poked around in the hole with a piece of wire and
all it was, was the non threaded end of the old stud lying in the bottom of
the hole. I remove it and finished drilling the hole. Now to tap it ready
for the coil. The stud hole in the top of the block is slightly smaller than
the tap, no problem, I just tapped that hole as well, it only left fine
thread lines in the top hole. The tapping of the bottom hole went smoothly,
once again slowly and carefully cleaning out the swarf regularly. The tap
just unscrewed through the top hole with only finger pressure. Coil
insertion, again required only finger pressure on the insertion tool. The
insertion depth collar can be placed on the insertion tool through the core
plug hole. Followed the instructions and broke off the tang, blew it out
with compressed air and presto job done. Screwed a new stud in the hole and
it went in cleanly with no binding. So now I have nothing to fear when I go
to remove the remaining three studs.
The bits I used;
Recoil Kit 7/16-20 P/N 34070
Small drill 3/16 about one foot long
Large drill 7/16 about one foot long, both made by Vermont American
Tap, from kit, extended to one foot long
Coil insert tool, also from kit, extended to one foot long.
The whole job took about 90 minutes max, and was done with the engine in the
car. I will also remove the remaining core plugs and clean out all the sand
and scale. I’ll post the photos when I get them developed
I hope this helps anyone who has the same problem, it ain’t that hard. if
you have any queries e-mail me off list.
Regards,
Jeff Watson.
1976 SII XJ6
1984 SIII XJ6 (with repaired head stud hole)
1985 SIII XJ6 Sovereign,
1985 SIII XJ6 VDP
1980 GSX 750 Suzuki
1970 Norton Commando Fastback.
All in Sydney,
Australia.
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