Here's an update and a summary since I got a few off list replies that
had some interesting insight and opinions.
The helicoil is installed and the hub slides on with no resistance.
The kit I used as the 5/16-24 part number 5528-5. This included 12
helicoils, a thread tap and an insertion tool.
According to the instructions I had to provide a drill bit and I found I
needed the handle from my snap-on tap and die set to fit both the
helicoil tap and the insertion tool although this is not mentioned on
the helicoil package.
In the end I did not use a drill bit because the required bit was 21/64
which I don't have and which is only 1/64th bigger than the 5/16
threaded hole that I was tapping and that had a stripped thread anyway
so I just oiled up the tap and cut the thread for the helicoil using
standard thread tapping technique.
With the helicoil installed in the newly tapped hole I used some fine
needle nosed pliers to grab the tang on the helicoil and break it off.
The tang is pre-scored and it broke off easily and I just needed to fish
it out of the hole.
Several people suggested using coarse thread 5/16-18 helicoils in the
hub to provide better purchase in the aluminum and then use standard
manifold studs which have the UNC thread on one end and the UNF on the
other. I had already bought the 5/16-24 helicoils so while that sounds
like a good suggestion I didn't personally go that route.
Several people mentioned dressing the tip of the tap so that it would
resemble a "bottom tap" and thread more of this closed end hole. I did
that on the bench grinder and this allowed the helicoil to install
correctly just below the surface of the hub.
I decided to just do this one loose stud and leave the others alone for
now. I had one reply that suggested that helicoils are not a good
mechanical solution because they don't fully engage the depth of the
thread of the stud and replacing all 12 may not be the best idea.
Vance has mentioned several times in this forum that he used loctite in
the good studs to dissuade them from moving which tends to exacerbate
the loosening process to start with.
I think that is it, not a bad job and one that I would have no problem
repeating if I had to. If I felt compelled to drill and especially if I
had to do more than one stud I would follow Bob Lang's advice and make a
jig or farm the whole thing out to a machine shop.
Thanks for all the suggestions and comments, I never would have tacked
this alone.
Stan
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