A Briggs & Stratton single-cylinder 6-horsepower engine that powered our 15-year-old Simplicity rototiller. Due to piston-ring problems, the cylinder became scored. A mechanic friend and I dismantled the engine and found a connecting-rod defect, too. Figured it would cost a few hundred bucks to replace the parts.
Parts not available! The option: buy a replacement engine. In searching for that, I learned the Simplicity company had chosen a "racing engine" (go-cart type?) to power the tiller, and had designed the machine around the engine's specific dimensions. Via many sources, I searched for a replacement engine, within both Canada & the U.S. Scads of emails & phone calls, but nobody could supply an engine that would fit.
Early on, I'd tried my best to contact the Simplicity company, but they'd been bought by Briggs & Stratton... and, so far as I could learn, Briggs had shut that company down. My inquiries to B&S went thud! (not interested in replying)
The upshot to this is that I had to dispense with the frame, drive train, and other basics of that tiller and buy a tiller (used, but reconditioned).