PTO lever not engaged ?  Push the clutch pedal down and block it.. does motor turn easier by hand ?

True! When I mounted my belly sickle mower, 1 bolt was a thread or two too long and it wouldn't turn over either.

If it won't break loose doing that there's no point in letting the next guy have an easy fix. 

Pull the valve cover for inspection...

Then pull the governor out for inspection.

A stuck valve can keep it from turning over as well. Normally if you could turn it over by hand with a stuck valve it will then stick open and keep turning over. Since you said it turned over hard I go back to the rust on the rings. It still wouldn't hurt to remove the valve cover and make each valve push down open by hand and see them come back up. Not many other things can go wrong setting other than rings and valves.  If it was in the bottom end you should have heard something going on before you shut it off the last time.

If you do find a valve that takes a lot to push it down put oil on the stem and keep working up and down until it frees up. If you do have dry  stiff working valves and no rust you need to find out why you are not getting ample oil to the rocker arms.  If it is dry you would need to remove the rocker arm stud at the back to make sure it has the groove in the stud.  One of the biggest cause of dry rocker arm/valve stems is when the stud with the groove is put in the wrong place. Just information in case, while I am thinking about it. I am not nailing your problem. 

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Pushing down hard is a relative term. Should have said (pry down hard) Valve springs are hard to compress by hand by them selves.

Dick L,  You are the best.  Sorry I will never get to meet you.

Good Luck!

Bill Long

Take the plugs out and spin it over a while with the plugs out after putting more oil in the cylinders.  Check for oil pressure while it is spinning over.  If you don't see oil pressure you need to prime the pump and do the same again. You need fresh oil everywhere it needs oil.

 

If it is now turning over it should be safe to pull start it. 

Do as Dick said, oil in the cylinder will make it turn over easier, but don't fill the cylinders as that will also lock up the pistons when you try to spin it. Best to put oil in the spin it withe plugs out before installing the and towing it. LOL Bob

Got a volt meter?

If so, what's your battery terminal and starter terminal voltage when trying to crank it over. 

You may have a weak battery, bad cable connection or a near dead starter (stuck brush maybe) if its not cranking over on a 12 volt conversion. 

But speaking of engines being stuck, a friend of mine had a stuck WD45 a few years ago. He tried everything to get it unstuck, and nothing worked. One day his cousin (Huge guy, about 6'7", 300 lbs, and strong as heck) came over and said, "Gimme that crank!" He put the crank in, and jerked up once, lifting the front of the WD45 up off the ground in the process, and it broke the engine free! They hooked the battery up and it started right up! Been running it for several years now. 

Some years ago I got a buddies old Farmall M that sat  outside for 20+ years unstuck with a 3 foot pipe wrench on the crankshaft and 12 volts to the starter followed by rocking it back and forth in 5th gear with a skidsteer chained to the draw bar until the engine would make a full turn without excessive binding.  

After it was loose we put in new plugs and ignition related components, cleaned out the carburetor and fuel line, changed fluids and drove the old thing around for a good hour without it missing a beat!  As far as I know he still runs it now and then and it has yet to ever give him trouble.     

Gerald J. wrote: I repeat, forcing a stuck engine over is a proven way to bend a connecting rod sideways that will add binding of the piston and the rod bearing leading to breaking that rod when running and the broken end of the rod often bashes a hole in the oil pan or block. Gerald J.

Is it stuck if it spins with the plugs out?

Syslogv4 wrote: Even with jumper cables it has trouble turning over unless the plugs are out.

Your question was how to check for spark. If it spins with the plugs out then check for spark with the plugs out with jumper cables. 

However you can check for spark without spinning the engine using only a screwdriver. With power to the coil, open and close the points. 

With a probe light check for power entering the coil, then check the coil out, if power there then check at the wire at the points. If you have power and opening and closing the points does not produce a spark you have either bad points or the points are insulated from ground. If you do not have power out of the coil you have closed points or you have a shorted out condenser.  Or at least a short to ground from a bare wire or something. Could be where the wire goes thru the distributor.    

 If you do not get power out of the coil with power going in then remove the wire from the out side of the coil and check for power. If no power out get a different coil.

When I was buying dead tractors I took a jump battery, a #14 wire with a clip on each end, a screwdriver  and a can of starting fluid. I clipped onto the coil from the jumper pack with the wire and clipped the jumper pack ground to the tractor. I then used the screwdriver to check for spark.   If I had spark I jumped to the starter and shot starting fluid into the carburetor to see if they would run at all. 

if it starts that way,  then you might just need a starter as the starter can drag your voltage down enough that it won't start....

Otherwise, points, condensor, coil.  

key on:  voltage to the coil, voltage to the points with the points open... 

none with the points closed.  

if voltage to the points with them open AND none with them closed, then it should run as long as the coil secondary is good.

otherwise clean your points, or jump the battery to the coil....  or both.

Don't spend much time with the points closed and the engine not running as that can burn something up..... 

It depends on how stuck the piston is and how much force is used to try and break it free in relation to how stoutly built the individual components are. 

For a reference during the power stroke a typical engine can easily see peak cylinder pressure 7 - 8 times its cranking pressure which even on a low compression engine could easily be 500+ PSI  http://performancetrends.com/Definitions/Cylinder-Pressure.htm

Multiply that by the piston area and even  a small engine like what B has is still seeing at least two tons of force being put on a connecting rod during every power stroke at high loads without doing damage. 

To take it further given the ~1 3/4 inches of  leverage that works out to a minimum peak crankshaft torque of at least ~ 600 foot pounds at 90 degrees from TDC. 

So can a push rod or crankshaft be bent by forcing them?  

Yep. Obviously it happens all the time but not from a guy using the hand crank nor the starter, not even likely by dragging the tractor in high gear, working against a dead locked engine.  

Even less likely so if multiple pistons are stuck being some of the connecting rods would be under tension while others are under compression even if they were all only a few degrees off TDC or BDC where the crankshaft would have maximum mechanical advantage.