Stripped subframe bolt R&R ....sorry, long...

[J123fs at aol.com]

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Hey all,
Thought I would send a quick run through of the quick and not so dirty
process I went through recently to fix my stripped subframe bolt on my V8.
Firstly, I had gone through all the archives and read all the posts regarding
how poss. ways to fix it, and the only one that made any sense to me was a
heilcoil.
This stemmed from many reasons: Mostly because estimates from body shops that
didn't laugh at me directly for asking quoted me at least a 1500 bucks
for cutting the frame open to put a new nut in there ...more than likely they
just didn't want to do the job....but toooo much for me to consider
paying,....... and they said it was an insurance job only, to be bundled
within the billing, most likely with crash damage.
Anyway, I also put a lot of though through the process, and figured I should
be able to do the job without the long task of dropping the subframe and
having to support the engine to get at the captive nut, a 4-5 hour job at
best without a lift, or good engine support.... In fact, I diid the whole job
in 45 min. on drive up ramps!
Also, before considering using a heilcoil seriously, I talked to the company
that makes them, checked out the info on their website, and talked to the
supply house I bought the kit from (45 bucks for kit with 6 heilcoils) to
make sure they would handle the stress and torque the car would put on them.
They stated that it would not be an issue, and if properly installed they
would be rated for the same torque as the materials they where installed
into. Their info also stated that the heilcoil itself is stronger than most
other "ordinary" steels, and made for this specific application (a heilcoil).

Time will tell though, and I guess I'll be the guinea pig....
Thinking through the task at hand, and armed with my trusty caliper, I
measured all related tools (Heilcoil tap, heilcoil, Id of the subframe mount,
assoc. bolts and depth of the nut up in the body) to give a clearer idea of
what I was working with.
Only then did I find that the supplied install tool for the heilcoil was too
short to fit up into the body to reach the captive nut.
Solution was easy: I just made one with another 12 x 1.5 bolt ground to mimic
the factory heilcoil install tool, allowing one way install of the coil, and
then the subsequent removal of the install tool, so you can break off the
install tang (long blunt rod inserted up into the coil, and one quick whack
to break the tang off).
I also realized that the heilcoil tap would not fit though the subframe mount
hole. Also, my backup plan to tap the internal nut out to a 14 x 2 mm thread
if all else failed would not work either...as that tap would also not fit
through the mount....
(But, I should say I was afraid to go out to 14 mm lest I exceed the
engineering maxim of making sure that the size of the nut was at least as
thick engagment-wise as the bolt is.... Which it is not, in the case of a 14
mm bolt... but only by a whisker!)
Solution: drill the subframe mount out with a 5/8 drill.... More than enough
room for taps...
Also, I sourced some brass sleeves (two stacked) to fit over the bolt to take
up the slop from increasing the id of the subframe center mount, although I'm
not sure if they are really are needed, or if you couldn't use another
material as a sleeve, like rolled alum flashing or sheet steel rolled around
the bolt tight.
So, I drilled the mount, ran the heilcoil tap in using a socket and ratchet
to get it up inside the mount, as a regular tap handle wouldn't work in those
confines, and installed the coil, whacked the end off, and installed a
antiseized grade 12.5 bolt, no major heavy, greasy work involved thank
you.....
Summed up, I think I'm happy with the results, and it was relatively painless
other than the hot metal flakes dropping on my arm when drilling the mount!
I also decided to use a split lock washer on the 12.5 grade bolt rather than
threadlock compound, so as to not potentially draw out the coil in the
future.
I DID use anti-seize so as to not run into corrosion again on the bolt/nut.
I tightened the new bolt down to 80 ft.lb, and it's holding well 30 days
later at the same torque.
I also purposely ran down some heavily rutted roads, and have been cornering
harder than I usually dare on the street during this period.....
No probs.
Again, Sorry this was long, but I thought someone may find the info useful in
the future if they are suffering from the same dreaded clunk, and bolt
failure as me and do not want to spend big $$ paying someone to fix it, or do
not want to get into the project of dropping a subframe.
Cheers,
John