A little dust on this thread but it will be time to mow soon.
Briggs makes a great little engine but my newer Troy-built self propelled quit on me the year before last.
Fuel, spark, were the first tasks and was ok so I was thinking timing or a loose or broken valve seat or retaining clip but they were also ok.
I then split the case and found the problem. It used to be that the gear on the crankshaft that drives the cam was milled in place out of the same good steel but I found that my cam gear was made of perhaps some kind of pot metal and was held to the crank via a keyway and it had split in half on its longitude.
I also found that the cam gear, which includes the cam shaft and lobes were made out of plastic. This assembly really did not show any wear and I just report it as an observation. I was able to get a new pot metal gear to put on the crankshaft and was up and running after that.
These finds were disappointing for sure but the mower ran great last year. I did strike back on two counts though as I start in the spring with new oil and a sharp blade as normal but repeat this in July when the weather becomes hot.
Not all people will disassembly their motors but I was fortunate enough to have taken two years of air cooled engines in High School Vocational.
Briggs makes a great little engine?...I say yes as they can run extremely well even when tolerances become sloppy. Just make sure to follow the oil change recommendations as 10 hrs can come & go quickly.