cranks but think it has a stuck value

i have a 76 cj5 w/ 78000 original miles sat for two years after bought at frame shop. came back cranks up but will have a bad jalt in the motor we think its a stuck value. need help dont know what to do and it a 258  

It's very easy to tell with a compression check.

First do a dry compression check of all the cylinders. Then any cylinder that comes up 20% or lower than the others, drop in a couple of ounces of oil through the spark plug hole.

Then repeat the compression test for that cylinder.

If the compression comes up, then that cylinder has bad rings. But if the cylinder compression does not come up you either have a bad head and/or head gasket, or a stuck valve or faulty valve.

If you have two adjacent cylinders with low compression and neither will come up with a wet test, then that usually means it's the head gasket and not the valve. Otherwise it's probably the valve.

Remove the valve cover and see if you can verify the offending valve and see if you can oil the stem and free it. But maybe it's sticking open because of carbon deposits on the valve or the valve seat. That will require you to remove the head to fix. Also check to see that the push rod, lifter and cam lobe are ok by observing the valves while cranking. All the valves should be moving alternately. If one is not moving, that points towards a defective cam, lifter or push rod.  

Does it start?
If not, I'd pull the distributor cap and see if it spins while you crank.
I pulled my hair out for 2 hours before figuring out that I had snapped my timing chain!!!  
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