Hilicoil ate aluminum thread! Need help.

[Konstantin Bogach]

Good people,

My first experience with hilicoils turns to be not good.  I restored 6mm
thread in aluminum (oil filter bracket, turbo oil supply flange), tried
to torque the bolt and... bolt is eaten, thread in aluminum is eaten by
helicoil.  I broke tang with hammer and rod. Visually was clear, bolt
easily went in through helicoil all the way when I tried it.  Until I
have a clue what happened I don't use helicol in aluminum any more.
A problem grew into bigger problem.  Now I have bigger hole which might
be OK for 8mm thread. Upper part of the hole is bigger then should be
for 8mm tap (7.5 mm) but lower part (bigger than half)  is good. But I
can not find stepped studs.  Dealer does not have it (at least one guy
from parts told me that). Stores I called don't have them.  Any advice
how to fix it or where to get 8 mm to 6mm studs?

I appreciate your help.

Konstantin Bogach.