"JustWait" wrote in message ...

On 12/30/2012 2:34 PM, wrote:
On Sun, 30 Dec 2012 10:21:34 -0500, iBoaterer wrote:


It's still not any stronger than the base metal, period.

There is more surface as the hole is bigger, period. The type of metal
or the thickness is irrelevant, more is more... period. I knew the
engineer wouldn't know ****, take the question to a technician
tomorrow
at work and have him explain it to you, LOL!

----------------------------------------------------

Both statements are correct however to what degree is the issue. In
the case of the Ford V-10, some of the "repaired" heads using
heli-coils spit the spark plug out again after time with the failure
being the heli-coil to head interface. The benefit of being able to
remove the spark plug with less risk of taking part of the head with
it is valid, but as someone pointed out, these engines do not required
routine spark plug changes. This is what got Ford in some hot water,
meaning trying to place the blame on spark plug replacements. The
primary reason was the type of aluminum alloy used that weakened over
time due to heat cycles.

Aluminum is a unique material in the respect that it comes in many
different alloys and hardening techniques, depending on application.
The last I knew there were about 10-12 different alloys typically used
in industry and several different heat treating and aging techniques.
I became somewhat interested in this when I considered building a
large, aluminum vacuum chamber that would be routinely subjected to
very high side wall loads of about 29,000 lbs. Talking to
metallurgists and mechanical stress engineers convinced me that it
wasn't a good idea because the typical "61T6" alloy would weaken over
time. I am not a mechanical engineer nor a metallurgist, but
considering the liability risk, I decided to stick with stainless
steel.