Small Engines (Lawn Mowers, etc.): B & S Intek V-Twin Cylinder OHV Engine, hairline cracks, hairline crack

Question
Hi. I have just replaced the conrod on the above engine after it just snapped while mowing. There was no damage in the cylinders etc but did have to replace the piston and rings as well (fine hairline crack on the old piston). After the rebuild I ran the engine in at half speed but after and hour or so the new conrod snapped again. My question is why would the conrod keep breaking? I would appreciate any help that you can give.

Answer
How many hours are on the engine?  Did you torque the connecting rod bolts?  Are the connecting rod bolts coming loose?  Is it just one cylinder, the same cylinder?  Cracked piston, never found one on a Briggs and Stratton...very unusual.  Is the cylinder sleave loose?  Has the engine been over-heated?  Most of the time when I find cracked pistons, in other engines, especially hairline cracks, it is because they have over-heated.

Let me know.
Eric