Small Engines (Lawn Mowers, etc.): B&S Engine Problem, briggs stratton, engine shaft

Question
Dear Mr. Kapsy,
I have a briggs&stratton model # 281707 , type # 0155 , 12 hp IC engine that has a problem. While mowing the other day, it sounded like something broke inside the engine, then it locked up and shut off. I'm a pretty good handyman around the house ,but I've never had to do any major repairs to an engine like this. I started taking some parts off the engine already. One of the first things that I removed was the cylinder head cover. While turning the motor shaft, I see both the intake and exhaust valves move in and out like they are supposed to, but the piston doesn't. I feel like that's where the broken part is inside the engine. This riding mower is pretty old now, we bought it at lowes approx.16 years ago.I know to remove the engine from the deck, that the belt pulley that is attached to the engine shaft on the bottom side of the engine has to come off. I removed the bolt that attaches the pulley shaft to the engine shaft, but so far I haven't been able to get the belt shaft off. I looked up inside the beft shaft and see there's a keyway in there. I sprayed a penetrating oil in there to hopefully free it up, but so far no luck. Is there a 'special' tool that's need to remove that belt shaft ? Also, on the top side of the shaft, I can't get the flywheel nut loose either. I'm debating if this engine is too old to mess with. But still..I have to get the belt shaft off. Thanks for any information you might provide. I know there's a b&s repair manual (# 270962 ) available for this engine, but so far I haven't purchased it, because I didn't know whether the engine was worth it or not.

Answer
Dave, Sorry, but this is a clasic example of a broken connecting rod...MAJOR REPAIr.  IF the tractor in great condition, I would suggest a short block. Any way, call a Briggs dealer and get an est. of cost and make your decisison on that. Best of luck....bob