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I have an older engine that is seized. It is a 1953 Desoto Hemi. How can I un-seize it?

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I have sprayed Sea Foam Deep Creep down the plugs and let sit for weeks. As well as transmission fluid. To no avail, this bad boy won't crack.

I have attempted to use a pipe wrench on the pulley, with a 10' solid steel pipe as an extension. It would not move. I suspect using a 20' extension might help the situation.

There has to be a systematic approach to get this turning.

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Tranny fluid is the best way ... if that doesn't do it, a tear down is in order ... JMHO. – Pᴀᴜʟsᴛᴇʀ2 Jan 21 at 1:32
    
Good question brother. – DucatiKiller Jan 21 at 6:43
    
Is this in your shop? If it is, you get the most interesting problem award of the year. You've always got a good one!! Brutal but telling, clearly you are tackling the hardest problems. Kudos bro. – DucatiKiller Jan 21 at 7:47
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Do you have any history of the engine? Do you know what has seized on it? For example a seized piston might be freed off with something acting as a penetrating oil down the bores, but a badly worn plane main bearing which has moved and wedged the crank will be unaffected by it. Let alone if someone has dropped a bolt down an inlet in the years since the engine was parked up! – Kickstart Jan 21 at 9:23
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Would love to hear how this turns out when you're done restoring it. What was wrong with it, what technique did you use to determine what was frozen, and how did you free it up. Inquiring minds would love to know :) Seriously my curiosity is killing me on this.. lol – cdunn Jan 22 at 20:33
up vote 36 down vote accepted

Stop trying to crank it and start beginning to disassemble it. Something is seriously wrong with it and forcing it will only break more stuff that might not already be broken. Especially if you have no idea what caused it to seize in the first place. The only thing more annoying than a seized engine is a seized engine with a sheared off bolt in the nose of the crank. Save yourself the hassle.

I would start by disconnecting the crankshaft from the camshaft and seeing if the bottom half can rotate when disconnected from the valvetrain. Looks like you've already done that so on to the next step.

If that doesn't work, take off one head, try again, then take off the other. Maybe a valve and a piston hit each other really hard and are wedged together?

Next, take off the oil pan and look up the cylinder bores. See anything funny? No? Remove the oil pump and remove the rods from the crank and begin pushing the rods and pistons out the top one by one. See anything funny with the bearings? The pistons? The cylinder walls? When all the rods and pistons are out, off come the main caps, the bearings and the crankshaft.

Then you can start inspecting the cylinder walls and the piston skirts. This will tell you why the engine is seized. The rebuild may then commence.

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Clearly a veteran opinion. I get the feeling the you've seen this movie before. Quit forcing. The long road of disassembly is actually the short road. Counter-intuitive, been there seen that advice. – DucatiKiller Jan 21 at 6:43
    
Oh yeah. Plus one for earning the knowledge. – DucatiKiller Jan 21 at 7:48
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I'm in the middle of doing this exact task. I mysteriously lost oil pressure while highway cruising. Pulled over and got it towed home. After I opened it up, turns out an oil sprayer had come loose 10 years after assembly, bounced off the crank and shattered a piston skirt. None of my theories were correct and I really had no idea what had gone wrong until I took it apart. – Jim W Jan 24 at 18:10

If Sea Foam and transmission fluid did not work, I would stop trying to crank the engine. If you force the engine you will likely damage it. If I had to guess, there is rust built up on the cylinder wall around the rings. Forcing the pistons past these rust rings will likely score the cylinder wall or ruin the rings.

My suggestion is not to risk it; tear the engine down and inspect what may be frozen.

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This is how I have gotten sunken engines working. Literally pour gallons of Diesel fuel inside everywhere... In through carburateur, Oil filler, literally fill it... Diesel work just like wd40... Let it sit a few days, then take heads and spark plugs out. drain the diesel out, just leave the 4 quarts or so in oil pan. Try to move it once with the wrench attach to the flywheel. Now if the engine was in good shape it might actually start turning. But your rings and bearing are probably bad, so you have to rebuild it anyway. So best to start taking it apart. Heads off first, then front cover. Then the crank. The goals is to do the least... but who knows how bad it was to begin with.

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Drown it in WD-40? It gets nearly anything un-rusted and un-stuck (though might take time to seep into tight spots - hence the idea to "drown" in it).

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