Some will try, just to defend Stihl:jawdrop:
Make sure you understand the law.
The assumptions about the con-rod, rope, stop, bending, so on and so forth, have been wrong.
The relationship between the piston, crank, and rod are very important when applying torque to the crank.
As I stated in the original thread about the rod failure, the con-rod has maximum leverage on the crankshaft at a point when the crankshaft center to rod journal center forms a right angle to the con-rod ceterline. At any point other than this the crankshaft leverage ratio increases.
In Trig trems, the side adjacent is the con -rod, the side opposite is the crank, and the hypotenuse is a line between the wrist pin center and the crank main journals.
If you seal an MS260 cylinder, then pressurize it with 100psi you will get a force of about 243 pounds on the piston. That same force will be constant at TDC, BDC, and everywhere in between. At BDC you will be able to move the crank back and forth with minimal effort. Put the con-rod and crank at the mentioned right angle position and the effort to move the crank toward TDC increases a great deal. Continue to move the crank toward TDC and the effort will lessen, although the force on the crown of the piston is constant.
That reduction of required effort is the same thing you feel when you draw a compound bow, or use a cam locking clamp.
If you place the piston near TDC with an uncompressable item in the bore, your ability to use the crank as a lever against the con-rod is greatly increased.
Putting it another way, If you put 100 lbs./ft. of torque on the crank you exert a much greater force against what you are compressing at 15deg. BTDC than you do at 60deg. BTDC.
I would imagine that Stihl's piston stop places the rod and crank in a relationship that favors the connecting rod.
Or, just use an impact wrench...
