Seized engine

I bought a old 1950 chevy pickup with a 216 engine. The engine will not turn, it seems to be stuck. My question is how do I try to turn the engine by hand with a breaker bar. I removed the spark plugs and poured mystery oil down the cylinders but it still wont turn. The previous owner said he drove the truck and parked it under the tree 5 years before i found it.

You could try to fill the crankcase as full as possible with kerosene. I don’t mean just to the full mark on the dipstick but as full as possible so that the crank and rod bearings are soaking in it. If you can get it up to the camshaft, that would be even better. Let it soak for a week or two.

Pull the timing chain cover and spray it down with PB Blaster or Seafoam. After a week or so, you maybe able to turn the engine over with a breaker bar. If you want it to run, you are going to have to rebuild.

It’s more likely that the cylinders are fused to the pistons and vice versa. I have not seen a stuck crankshaft in an old engine. As I recall, these old guys had cast iron, not aluminum pistons so you can have rust on the cylinders as well as the pistons. You might want to pull the head to see what you have, an easy job with a Chevrolet stovebolt 6 and no emission controls. If it’s really rusted, it might require the engine to be pulled and then crank removal so you can press or pound the pistons down and out. Then new oversize pistons, cylinder reboring and valve regrinding are next as well as crank remachining as needed. These things didn’t have con rod inserts so new undersize rods may be in order unless you can convert to rods from a few years later (1954?) that did have bearing inserts.

Keep in mind that an old pickup parked under a tree likely had some major issue or it would have remained in service.