I said in my post that the numbers may not be exact but would be close. Here are some specs I found on cast aluminum.
http://www.substech.com/dokuwiki/dok...um_alloy_443.0
there are others but this one had the least shear strength at 13,200 psi. My figures were in psi because of the way I figured the contact area of the bolt. Using this formula ,
http://www.engineersedge.com/thread_...olt_stress.htm , is how I got my numbers, witch will be different with the new number of 13,200. The amount of contact area per bolt is .38725 sq inch. Using .3331 as the Max, .3643 for the Min, .500 for the length, and 16 threads per inch.
13,200 psi x .38725 sq inch = 5,111.7 lbs x 5 bolts = 25,558.5 lbs
Wow these new numbers are working in my favor.
Now being according to the chart the yield strength is 10,150 psi we only need to reduce the 25,558.5 lbs by about 30% (not 50 - 60 ) we are at 19,660.38 lbs or lets say 20,000 lbs to keep it easy. Then figure in the safety factor of 2 you say, we are still at near 10,000 lbs.
Now one must keep in mind that the whole rearend is only held on with 6 bolts. And they are in aluminum. I have heard of a few having problems when the bolts work loose on the tubes but that is pretty few compared to the total amount of them out there. Some of the these tractors have been working for what around 30 years now. Just think of all the twisting and jarring and banging they have gone through just mowing. Then how about all the snow/dirt plowing, cart/tree/whatever pulling they have seen.
I am not an engineer and don't claim to be one, and these are garden tractors not Airplanes.