My Riding mower has an 8 year old Briggs & Stratton 14.5 HP OHV Engine. Engine always maintained properly and has run well. While mowing, engine ran well for an hour and then suddenly quit for a split second, and backfired as it came back to life. I continued to mow and it did it again, the third time, the engine died, and then would spin easily but not restart, I pulled the plug and found NO COMPRESSION and had proper level of oil. Any ideas on what happened? Rod, Valve, push rod? Ever heard of this problem before with this engine? Thanks, Mike