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EM stud removal revisited
Hello, Club!
I have just finished removing 2 broken EM studs. This is my 4th time on
3 Audis. Here's some new info. For all new 44-chassis Audi owners on the
List: the EM studs breaking is not an "IF" occurrence, but rather a
"WHEN".
I again broke a screw extractor inside the broken stud. I never learn,
do I? However, this time I managed to drill the extractor out of the
stud. It is doable! All you need is a Dremel tool and a good, American
made, 1/8" tile drill. It looks like a tiny spear with a droplet-shaped
carbide head. Just be very careful with dead-nuts centering the starting
point and use plenty of oil. I used Castrol Syntec. Yeah, I know, it's
decadent, but I don't have a drop of mineral oil in my garage ;). And
be patent, very patient.
I strongly suggest NOT to attempt doing it with the head still on the
block. Sorry, folks, but the head will have to come off.
Once you have drilled the broken easy-out completely through, you can
collapse it's remainder inside the hole. Oh, make sure that you drilled
the broken stud completely through beforehand. The threaded bore in the
head is 20mm deep. The threaded portion of the stud is 13mm. That means
that you have about 7mm of empty space behind the broken stud. Use a
drill stop as not to accidentally drill into the soft Al, once you have
gone trough the forged steel stud.
If you broke an easyout, while trying to remove the broken stud, DO NOT
attempt to extract the stud again, it's not gonna happen. You are
looking to mill the stud out and to re-sleeve the hole. I've done it
once in '94 and it worked very_well. This time I did it in two more
holes.
Here's how:
1. Fabricate a mandrel. I used a 1/2" thick brass plate, coz brass is
"soapy". I would imagine regular steel will work too. Just don't use Al.
The mandrel is rectangular and has four 5/16" holes (A,B,C,D) in the
corners. 5/16" is a hair under 8mm and allows a more precise positioning
of the 8mm studs in the mandrel. The holes should be right over the
ADJACENT IM mounting holes. Measure the distance on the head.
Not to scale:
________________________
|
O O |<-5/16", 4 places
A B |
|
|
|
|
|
|
C D |
O O |
|
________________________|
Now drill two more holes, (E,F) so that E is equidistant between A and
B; F is equidistant between C and D:
________________________
|
O O O |
A E B |
|
|
|
|
|
|
C F D |
O O O |
|
________________________|
E=5/16". F=27/64".
2. At your local Home Depot get a special tool under $10 for drilling
screw holes in the wood. It has a 5/32" drill bit inside of a spring
loaded 5/16" steel sleeve. Also get a 1/2"-13 bottoming tap and a 27/64"
drill bit for this tap. They come as a kit for under $10 also.
Also buy four 8x1.25x30mm socket head bolts.
3. At you local Hechinger get several forged steel threaded inserts, a
coupla bux each. Those inserts have treads: 1/2"-13 on the outside and
8x1.25mm inside. I don't like to use Helicoil coz I feel it's less
strong, being essentially only a steel spring with a diamond shaped
crossection.
4. Position the mandrel over the EM port and bolt it on with the four M8
bolts through the holes A,B,C and D to the ADJACENT PORTS for the IM.
This will effectively position the holes E and F over the broken EM
studs of the EM port in-between those adjacent IM ports.
5. Use the 5/16" retractable drilling tool for drilling the broken stud
using the 5/16" hole E in the mandrel as a guide. this will get you a
5/32" hole in the broken stud, AUTOMATICALLY centred by the mandrel's
hole E. Drill completely trough the stud, but don't damage the Al of the
head's body under it.
6. Use a regular 5/16" drill bit on the newly drilled 5/32" hole in the
broken stud. Now you will be using the mandrel's hole E as a guide once
again. The net result will be the 5/16" hole in the head, where once the
original M8 broken stud in the original M8 hole used to be. Once again,
use a drill stop to limit your drilling to the depth of the original
hole in the head. Yes, you WILL ruin the thread in the process, but it
is not salvageable anyway.
7. Undo 4 bolts, holding the mandrel and flip it vertically 180°. Now
you have the 27/64" mandrel's hole F where the hole E used to be over
your freshly drilled 5/16" hole in the head.
8. With the grinding stone in the Dremel tool or by any other means
grind off the pointed tip on the 27/64" drill, that came in the 1/2"
tap/drill kit, effectively turning it into an end mill. If you have
access to an odd sized 27/64" end mill (naturally, a 4 fluted one is
preferred, but not essential), you could use it instead. DO NOT use a
regular drill bit unless you're using it with a drill press. Otherwise
it WILL grab, bind and mess up soft Al of the head.
9. Using the hole F in the mandrel as a guide mill the hole in the head
to the 27/64" size to the ORIGINAL depth of the hole in the head. Use a
drill stop!
10. Cut the 1/2"-13 thread in the freshly milled 27/64" hole with the
tap from the kit.
11. Screw in the 1/2"-13 treaded insert.
12. Screw the new OEM only(!) stud into the insert. Viola!
A disclaimer: I was successful in doing this 3 times. However, YMMV, it
is a VERY delicate job! If you do not feel 100% confident, I suggest you
leave it to a pro machine shop.
--
Igor Kessel
'89 200TQ -- 18psi (TAP)
'98 A4TQ
Philadelphia, PA
USA