Briggs Vanguard, 15 hp OHV Model 280777 Type 0112.01 Code 94121154A
Simplicity Brood Moor...

The oil was checked and gas was checked prior to starting, the mower had been sitting for 4 to 6 weeks due to cold weather. I decided to started it and ran it at normal start speed until It warmed up. I maintain my mowers very well as they are my lively hood!

Ok, it will not start! I was blowing leafs, just with the deck no blowers attached, the mower ran fine for well over and hour, I rode the mower to my mothers home and while I was riding I noticed a pinging that seemed to be coming from the deck, I checked it and discovered it was coming from the motor, I being DUMB ignored that, and kept riding thinking a bolt or part of the covers was loose because that's what it sounded like!

The pinging sound wasn't very noticeable, but after reaching my mothers I used the throttle to speed the engine to engage the PTO, the motor seemed to ping louder so I very quickly lowered the RPMS and listened, the pinging became soft again. So I engaged the PTO at a lower RPM and proceeded to blow the leafs, only going a short distance the mower seemed to be OK, so I again attempted to speed the rpms up slightly and again the pinging became loud, so I lowered it, and it seemed to FLOOD OUT and the pinging got pretty bad and it went dead. Will not start and seems to be hard to turn over..

I did notice the pinging sound before I parked it for winter but forgot about it until this happened.

Any suggestions, or information would be of great help, I am currently not able to work due to illness and money is very tight in our home.
I do have some mechanical experience and feel very comfortable working with engines, but like information as I am not a professional mechanic!