How to free up a seized engine?

[SVOVET]

What's the best way to free one up? Ultimately my plans are to rebuild the engine, but if it can be un-seized that'll work for now.

[Ken Potter]

Is the engine still in the car? Automatic transmission fluid has penatrating qualities that can "unstick" rings from cylinder walls. If you can't or don't want to pull the engine you can pull the spark plugs and squirt a VERY SMALL AMOUNT into the cylinder. If you put in too much you can hydraulic the piston and damage / crack the piston. It is best to do this with the engine on a stand out of the car with the head and oil pan off so you can see when the trans fluid seeps / makes it's way past the rings. This also obviously keeps from hydraulically damaging the pistons. It may take several applications and a pretty fair amount of time but it will break free. Use only easy / gradual pressure when trying to turn the crank. I also recommend getting some kind of crank turning tool that bolts to the inner ring of the harmonic balancer. I prefer not to turn the crank by the crankshaft bolt. Also be sure to turn the engine only in the correct direction. You can also rotate the engine on the stand and apply trans fluid to the crank and connecting rods ( both ends ). It's also kinda messy so get a pan large enough to collect all the drippings. I've done this with a flat head 6 so I'm speaking from experience... It takes awhile. Good luck.

[SVOVET]

Thanks for the input. The engine is still in the car. This particular car will eventually be a resto project, so the engine will come out. I currently have the plugs out and applied some Marvel Mystery Oil. It has been 3 days so far. I'm sure it will take a little while. I'll check on it again in by the end of a weeks time.

[Ken Potter]

The old Marvel Mystery will also work since it's just a more viscous ( SP? ) type of trans fluid. When I finally cranked the flat head 6 I mentioned it smoked for only a short while. I let it get up to temp and then changed the oil. It's the engine in my 55 Willys Jeep wagon. Only 90 horse but makes something like 380 lb / ft at 1700 rpm. It's slow but it will climb a practically straight up incline.

[SVOeric]

One thing I have used in the past was disel fuel

I have also used ATF too.