> If you
> recall, the DPO had run some oversized bolts into the
> trailing arm to secure the brake backing plate and the
> bearing housing to the trailing arm. Now, I must choose which
> heli-coil kit to use to repair the trailing arm, I would
> appreciate any and all votes if you would take the time to
> check out my choices. They can be found at
> http://www.mcmaster.com/ and enter either 90245A053 or
> 92070A337. One is a thin wall, the other thick wall. I am
> concerned because the thin wall claims to be "lightweight"
> (duty?).
First of all, those aren't "heli-coils". Heli-coils have the smallest
possible outside diameter; they literally look like a coil of wire instead
of a sleeve with threads. I believe the brand name for what you've chosen
is "Thread-sert" (or, since they're the key-locking variety, "Key-sert").
And you've left out one piece of information : what size did the DPO tap
those holes out to ?
My feeling is that, if you can match the threads of the oversize bolt used
by the DPO, you should do so. Otherwise, chose the insert that will let you
cut clean threads (with no signs of previous threads) in the hole, WITHOUT
making the walls of the hole too thin. Since I suspect this is impossible,
you should probably either replace the trailing arm or have the hole
professionally repaired by filling it with weld, drill & tap to the original
size.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190120214431
Normally, the "heavy" Key-sert is slightly stronger, mostly because it's
outer threads are larger and so get a better 'bite' into the relatively soft
aluminum. The strength of the insert itself is not an issue, because the
aluminum is much weaker. But in this case, a larger insert means less
aluminum left to hold it. Especially given that this joint is mostly loaded
in shear (ie at right angles to the stud, rather than along it's length),
the trailing arm itself is the weakest link.
Besides, the original threads were strong enough. It's corrosion that
destroys them, not lack of strength.
Randall
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