Stuck Motor

[Had]

What is the best way to unstick a stuck motor.

[Barnyard]

A lot depends on what is causing it to be stuck. It could be a stuck valve or frozen piston ring. I have seen starters stuck that kept the engine from being turned over with a hand crank. A froze fan pulley can even keep the engine from turning if the belts are on it.

[Had]

My guess is stuck ring

[Barnyard]

Will the engine turn backward? Take the starter off and gently pry on the starter gear in the reverse direction..

[Barnyard]

Here is what we did with one of mine at RMCF a few years ago. viewtopic.php?f=1&t=85432&p=680940&hilit=head#p680940

[ntrenn]

Ditto on tracking down the root cause first...i bought the 65 loboy with a stuck motor.
..bought it for the tires.
On that one...a water leak in the head trickled down a bolt between 3 and 4 and rusted the bolt in two...then continued on down into 4 and stuck the piston in the liner....
After pulling the head and unbolting the rod from the crank....a block of wood and a hand sledge broke it loose. That method was suggested by an old timer on this board.
Tractor is on its 5th or 6th season since i got it going...

[Landreo]

If it is stuck from something internal then I would just pull the head and look. Valves are easier to unstick with the head off and any stuck pistons are easier to unstick with the head off. If it is due to rust in the cylinder, then I will make a wood puck the size of the piston and tap on the stuck piston(s). I have also used a hydraulic jack to push on the wood puck. If the stuck piston is in a cylinder with lot of rust or I suspect rust is the source of sticking then I do not use penetrating oil but clean the cylinder with brake cleaner and a shop rag to remove any oil. I then pour in some Evaporust and let is sit for a few weeks. The Evaporust will dissolve the rust and either the piston will move easily or I will put the jack back on. Once you use penetrating oil then it is hard to use a rust remover since the oil will prevent the rust remover from contacting the rust.

I just did two engines in the past 6 months, stuck for many years, a All fuel Case S with two stuck pistons did well the Evaporust and a jack. The other, a JD AR, never broke free with evapolrust but took a 20 ton press to finally remove the piston without damage. Evaporust is my go to method for removing stuck pistons due to rust.

[Barnyard]

Of all the Cubs I have owned with stuck valves (and that is a lot), I have never had to pull a head to unstick them. Usually takes under an hour.

[Landreo]

I may get rustier equipment than most. If it is stuck enough to prevent turning then I just pull the head and look around. Forcing it may bend the valve stem. Been there, done that, easier to pull the head and not bend the stem.

The OP gets to decide what risk they want to take.