You have evidently gotten the timing gear out of time! Easy to do when reassembling after opening the case. I use a piece of masking tape, or heavy thick wheel-bearing grease to hold the cam in place, then carefully lower the sump into position!

I couldn't say for certain what the cost would be. You will have to poll some machine shops in your area to get a feel for the prevailing rate. Automotive machine specialist type shops will be the best to check with as they have the equipment and expertise to handle a job like this. To them, it's actually an everyday event to cut a cylinder head for oversize valves in the quest for more power. Doing the same to an engine block (in your case) to correct for damage is not all that different, for them.

****"I have an 18HP Briggs twin with same symptoms."*** How much "the same" is YOUR 18HP Briggs twin, to the example machine in the OP (who, by the way, has not bothered to reply yet)?? But to answer the portion of the question that COULD apply to ***"wouldn't a nonfunctioning float valve cause the flooding to happen at all times, including parked in the shed for days or weeks between uses?"*** Yes, it would "attempt to flood" at all times, BUT, if your engine is fed by a fuel pump (instead of gravity) the faulty float valve can still leak enough fuel to flood the engine and cause "hard starting hot", simply by the amount of fuel in the fuel hose between the output connector of the fuel pump and the carb float valve. If the engine were stone cold....that same amount of fuel leakage would not hamper the engine from starting up (could help actually as it would be a "rich mix", which a cold engine wants for starting). The fact that YOUR engine is hard to start after a hot shutdown could be due to flooding temporarily because of the scenario I described, but not filling the engine crankcase with raw gas during storage because your engine might be "pump fed". You did not state whether pump or gravity, so I can't say how exact your situation is to the OP's situation, and since that person has not yet divulged the same info.....it's anybody's guess whether the engine configurations are the same. Could be, but so far....no proof! The small amount of fuel leaking into the engine intake after shutting down a pump fed carb could certainly cause "hard start hot from flooding". BUT, that small amount of gas would evaporate and be gone long before it could make its way into the crankcase (the engine would still be somewhat warm when all the fuel finished leaking out of the carb and estabilshed a "stable level" in the bowl. Another thing I will toss in here, and forgive me if I seem to be making "an assumption". You are not by chance "using the choke" when you attempt to restart the engine hot, are you. Before you get all defensive, I have had a couple of cases where an owner/operator complained of "hard start hot" only to learn (by chance) that they were ALWAYS "pulling the choke" to start!!!!! HOT or COLD. Remember, hot engines flood at the slightest provocation, but cold engines "like" a shot of gas.

Walt, thank you so much for taking the time to think this through and write about it in detail. I drove to Springfield today in hopes of talking to a mechanic at a huge power equiment business there that is well known for parts and service...unfortunately it has closed and there is no "we've moved to..." sign. This economy is killing everyone. Oh well...sleuthing with you all, I guess! :) Anyhow, to answer some of your comments, I have run two tanks with SeaFoam but seen no improvement since using it. I have a stupid qustion regarding the ground for the battery...I only see the two main battery cables (pos. and neg.) and then they lead underneath the battery compartment/seat area to places unknown and impossible to see or get to without removing the entire metal cover for the mower. I've had experience dealing with battery problems on my pick up truck and I know there was a separate ground wire that was attached with the negative cable for my truck but I don't see a separate ground for this machine. Is it bundled with the negative cable? When I removed the battery from it's compartment, I still can't see where the cables lead (although I saw a white plastic flywheel of some sort under the battery area, what the heck is that?? Just curious!) Is there any way to get to any of this stuff without removing the mowers metal cover? I was going to remove the starter and take it to a mechanic to test it but couldn't figure out how to get it off the motor. I asked a neighbor who rolled his eyes and said "It's only 3 bolts!" but when he looked at it, he couldn't figure out how to get it off there either (made me feel better...the little eye-roller!) Regarding your comment: IF you have a GOOD set of jumper cables, jump directly from the batter to the starter as you said you did with the charger and see what happens. The contacts of the starter solenoid that you hear clicking may be burned until they do not conduct enough current anymore. By passing as above may help tell if this is a problem but would need more checking. I have a good set of automobile jumper cables..I can definitely try this and see what happens. I'll continue to post if I have any luck with this. I think it might be time to junk it and get something new but I really, really hate doing that. I'd rather fix it if it's possible and cost-effective. It's a shame that this engine has a history of this problem yet Briggs&Stratton never dealt with or addressed it. Oh one last thing, would a bigger/stronger battery help in any way or not since you said the starter is maxed out when conditions are ideal? Thanks again!