Crankcase Gasket

Engine would kick back when trying to start. Like the engine had too much compression or was out of time. I took the engine apart and checked the timing; I had also taken the head off and checked the cylinder and valves. Put the engine back together using the new gaskets, adjusted the valves and installed a new keyway pin in flywheel. Put on a new ignition coil and replaced the drive belt. Now the lawn mower cranks over and starts.

Disconnect Battery
Disconnect Starter and Electrical Wire.
Remove Engine shroud.
Remove Intake manifold w/carb. Remove muffler.
Lower mower deck and unbolt mower transmission and blade pulley from crankshaft.
Unbolt and remove Engine from lawn tractor chassis.
Drain Oil.
Unbolt and remove cylinder head & remove push rods.
Unbolt and remove bottom crankcase cover.
Remove cam shaft.
Remove broken Connection Rod (note connection rod orientation on crankshaft, it will only work one way).
Push Piston up and out the cylinder.
Inspect engine case, crankshaft, piston and cylinder for any damage or scoring.
Remove retainer clip from connection rod piston pin and press out pin far enough to remove old connection rod and attach new one. Push connection rod pin back into place and replace retainer pin clip.
Check piston rings for any damage and replace if necessary.
Hone piston cylinder.
Using a piston ring compressor tool, compress piston rings on piston.
Lubricate piston cylinder. (I use Lucas Assembly Lube but regular oil will work) and slide piston back into the cylinder making sure the connection rod is orientate correctly.
Lubricate crankshaft with oil and attached connection rod. Torque to required specs.
Reinstall camshaft making sure to align timing mark on camshaft and crankshaft.
Remove and clean engine block and cover of ALL old gasket material.
Remove oil pump cover on the crankcase cover and remove oil pump gear and drive pin.
Place new crankcase gasket on engine block and replace crankcase cover. Torque to specs.
Align oil pump drive shaft with camshaft slot, replace gear and replace oil pump cover.
Remove and clean cylinder and cylinder head of ALL old head gasket material.
Place new cylinder head gasket on engine block, replace cylinder head and Torque to specs.
Remove OHV cover.
Loosen rocker arms until you are able to replace push rods.
Rotate engine until engine timing is at TDC. Adjust rocker arms to correct gap setting between rocker arm and valve.
Replace engine to lawn tractor (reverse of removal procedure).
ADD NEW OIL.
When you start using tractor again, do NOT run under full load for the first 5 to 10 hours. Change oil and filter (if equipped) after 10 hours.

Unhooked throttle cable.
Unhooked wiring and fuel line.
Removed muffler.
Removed pto clutch.
Removed transmission drive pulley.
Removed engine mounting bolts.
Removed engine.
Removed engine sump pan.
Cleaned old material from sump.
Installed new gasket
Installed and torqued sump.
Installed oil pump with new o-ring.
Reinstalled engine.
Reinstalled engine mounting bolts.
Reinstalled transmission drive pulley.
Reinstalled pto clutch.
Reinstalled muffler.
Hooked wiring and fuel line back up.
Reinstalled throttle cable.
Filled engine with oil.

Remove the oil pan is all and then remove the oil seal from the oil pan and clean the old gasket and replace the new one, and replace the oil pan, everything worked good.

I removed the engine from lawn tractor and disassembled and inspected and cleaned and organized parts. I honed the cylinder lightly because it was still in great condition, but I felt it needed that for the new ring set. The old rings were fine, but the engine is 14 years old so while I had it apart, I felt that was best. Everything went back together as expected and the engine runs really well. the only thing that is noteworthy was torquing the bolts and being very careful putting the sump on, so you don't damage the crank seal.

Disassembled motor and replaced parts

completely disassembled engine except for crank and flywheel and reassembled using new parts and gaskets I also reseated the valves while the head was off

Removed engine, removed head, valves, opened case to check rings. Rings OK, replaced piston and side case gasket. Removed valves, lapped valve seats, replaced valve stem seal. Replaced head with new gasket. Job complete.

I jumped the gun initially and pulled the engine from the tractor, thinking the connecting rod had broken. I should have checked the valve push rods first. That would have saved me the time of removing the engine from the tractor and replacing the pan gasket and crankshaft oil seal.
It was pretty simple after I determined that my problem was the push rods. I removed the bent rod installed the new one I purchased from eReplacementParts.com. Adjusted the valves(You can find several youtube videos to guide you through this procedure). The engine started right up and I mowed about two hours with it this weekend.
I wish I could tell you why the push rod bent, but I can't. If anyone has an explnation I would love to here it.

Rusty old bolts required soaking them in penetrating oil; waiting a bit; and then long breaker bar to free them.

Replacing the cam shaft was easy (after watching a youtube video) for tips on how to remove and re-install the sump pump shaft.