18.5 HP OHV LT INTEK BERNING UP STARTER IT DOES NOT HAVE ENOUGH BALLS TO TURN IT OVER

Have the starter motor checked out as it is probably has brush problems or gunk on the commutator check terminals are clean and not rusty

check power suply to starter possible faulty
selinoid

change oil n filter plugs and fuel and air filter

you should have a square plug on the side of the block usually on the starter side of engine

sae 30 in winter sae 40 in summer i preffer rotela

From your description it seems that the starter is not engaging to turn over the engine. First ensure all the connections of the thicker cables to the battery, starter and tractor frame are clean and tight. If starter motor is turning but still not engaging it will mean that the pinion on the starter motor is binding on the shaft. You can buy a new starter pinion gear from your local B & S agent.
To replace pinion, remove starter motor from engine, remove old pinion and put on new one and reattach starter to engine. If fuel & spark are right you should be up amd running.

sounds like starter is bound up,take it off engine and apply battery voltage to battery cable connection on starter and see if starter will turn over if not the starter is bad

Sounds like the voltage regulator is bad--will run the battery down!

IF THE ENGINE STILL TURNS OVER YOU MAY BE ONE OF THE LUCKY ONES ON THE OHV ENGINES PULL THE VALVE COVERS AND SEE IF ALL THE TAPPET RODS ARE THERE IF NOT THIS COULD BE WHAT IS BOUNCING AROUND INSIDE
WORST CASE IF ENGINE WILL NOT TURN OVER THE CONNECTING ROD TO THE PISTON COULD BE BROKEN

check the safety switches one of them are bad