Ok here are the results from the testing lab,
Please notice that the bolts have broken in the threaded portion of the bolt, which is where they are typically supposed to break. They all rested right at 100,000psi.
Per the manufacture, failures of the type you described have always been attributed torsional over-load.
Below is the actual response from the manufacture:
"It has been our experience that with field-failures of the nature that you are describing, they have always been attributable to torsional over-loading of the product, meaning that the product was over-torqued, or tightened-down too hard, during installation. It is our recommendation that the product only be installed “hand-tight with a wrench”, to eliminate the stresses that are introduced when the product is torsionally overloaded".
Results:
Serial# Width Dia. or Gauge
Area Yield (lbs) Ultimate (lbs) Ultimate(psi)
I 7/16-20 .1288 12,791 99,300
2 7/16-20 .1288 12,771 99,200
3 7/16-20 .1288 12,998 100,900
Now on to the testing we have done here... In order to figure this out we have been eyeballing this for hours and this is what we have come up with.
The point of failure has had us really questioning things
So we have gone through the installation a few times and this is what we are seeing.
When you install the bolt in a 3216 head on a standard cub spring or other wise you will need to install with a 3243-3S spacer to take up the 1/2" hole in the head to make it a 7/16" we noticed on the broken bolts that the radius area of the bolt was shiny and worn, and you guessed it the 3S Spacer stops there and didn't make a flush contact with the head..
We then installed a washer on the bolt (like it should be under the head) and then installed the 3S Spacer to see the head have a full contact on the load bearing surface
Now also as noted in several conversations previously on S Cub .org the 3S Spacer protrudes through the head bracket of the tail wheel and into the spring, most times we see this part smashed and out of round because it don't really fit into the spring with a 7/16 hole. ** Note we didn't invent any of this we just PMA'd the parts so we all could get them when we need to.
So We still will offer the $40 return for those that would like to return the bolt. At this time we will not be selling any of the Eye Bolts and in the future but will be changing out PA-18 Tail spring to a 1/2" attach hole to delete the use of the 3S Spacer in future installations.