Alton, please take a look at this video:
http://www.jackssmallengines.com/jacks-parts-lookup/briggs-stratton-model-locator.aspxI think the Model is probably 31P677, and your mower might be a John Deere, but we need the Type as well as the Model to find the parts list, so please run through that video and see if you can supply all three numbers. (The Code tells us the date of manufacture of the engine.)
I'm not really clear on how many hours it takes to wear out the camshaft so it needs replacement - it is hundreds of hours, not thousands though, this is not a car engine. What is probably more relevant here, is that the slight wear on the moving parts that increases the valve clearance and causes a problem, can happen right from the start, as the parts bed themselves in.
