Only time I had ever seen something like this happen was on a Craftsman lawn tractor in the late 80's - it was fairly new at the time, so guessing a '87-'88 model. Think it had a Briggs, but that was 10's of thousands of gallons of beer, whiskey, rum, gin, and who-knows-what-else, ago ... the mind is a little "pickled" ...
The reason it blew up? After my buddy melted the engine down on his '85 KTM 125MX running wide-open down the street in the rain with me on the back, we were bored ... so why not BOTH of us hop on his dad's tractor and see how many wheelies and burnouts we could do!
Every day after school for about 3 weeks straight, I'd head to his house, we'd push the tractor out, I'd hop on the fender and we'd go to a section of his driveway that was on a hill, and let 'er rip! Almost flipped it over backwards a few times, so I started sitting on the hood. Front end would STILL pop up!
This was after years of mowing commercially with it at some condos his dad built, with he and I freewheeling it down those hills at 40 MPH, throwing it in reverse and doing a smokeshow in the street, etc., etc. ...
You have NO IDEA the amount of abuse this thing took! I can't even put it into words. Nothing built in the last 30 years could withstand this!
One day his dad was mowing, and BAM! Rod came out the side of the block! I'll never forget walking into that one day. We go down the basement from outside, and there's his dad holding the mangled rod and piston in his hand, engine parts scattered all over the bench, he hears us come in, he turns around and stares at us with what I thought was a red glow in his eyes ... "SEE WHAT YOU ASSHOLES DID??" He was NOT happy!
Ahh, the good ol' days!!