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Repairing Seized Engines

Just because it's stuck doesn't mean it's down for the count

| May/June 2003

  • Figure #2: Removing a seized piston with a mallet and a block of wood.
    Figure #2: Removing a seized piston with a mallet and a block of wood.
  • piston sketch
    Figure #1
  • Figure #3: Expanding a piston ring to fit a piston.
    Figure #3: Expanding a piston ring to fit a piston.

  • Figure #2: Removing a seized piston with a mallet and a block of wood.
  • piston sketch
  • Figure #3: Expanding a piston ring to fit a piston.

Much as we like working on our old engines, there's a limit to what many of us can handle, and a seized engine is pretty much that limit. But don't throw in the towel if your engine is stuck, because a little insight and the right approach can often get that old iron spinning once again.

Engines seize for any number of reasons; rust (usually from sitting too long), excessive heat (from running the engine without coolant or oil), or for some mechanical problem, such as a foreign object in the cylinder or a crankshaft bearing failure.

If you think your engine is seized, you need to confirm that before doing anything else. The first thing to do is remove the spark plug (s) and try rotating the engine. On the small engines most of us are working on you can bet that if you can't rotate it by hand, it's probably seized. On larger engines you'll want to use a breaker bar to see if it will turn.

Assuming everything is okay with the crankshaft, the easiest and cheapest thing to try is penetrating oil. This works surprisingly well, particularly with engines stuck from years of sitting out in the rain, where water has rusted the piston rings to the cylinder.

Everybody has their favorite penetrating oil, but I like P'Blaster. Start by shooting oil down into the cylinder through the spark plug hole, and don't be shy - use a lot of the stuff. Wear goggles in case the penetrating oil sprays back and hits you in the eye. If you have the patience for it, spray some in every day for about two weeks, followed by gently tapping on the cylinder wall with a hammer handle. This sets up vibrations that help the oil penetrate between the rings and the cylinder wall. After soaking the engine for a while try rotating the crankshaft. If you've been patient, and if the engine wasn't too badly rusted, it will usually break free and rotate. If it doesn't, hit it with more penetrating oil, and make sure you use enough. I've found that about half a can per cylinder is right. If it still doesn't rotate after four weeks of daily treatment, it's time to resort to more serious measures.

Pulling it apartIf penetrating oil doesn't work it's time to remove the cylinder head and, most likely, the crankshaft. On smaller stationary engines this is pretty straightforward, but on larger tractor engines you'll be getting into quite a bit of work. On a multi-cylinder engine it's often possible to discern which cylinder is stuck, sometimes just by looking into each cylinder. If you're lucky and you can figure it out, remove the end cap on the connecting rod of the offending cylinder and then rotate the crankshaft so the crankshaft throw for that cylinder is out of the way. With the cylinder head off take a mallet and try and pound the piston out, placing a block of wood on top of the piston so you don't bang up the piston with the mallet. Make sure the wooden block is clean - you don't want to mar the top of the piston with sand or small rocks. Make sure the piston can slide out the bottom of the cylinder without smashing the crankshaft -you don't want to make things worse than they already are. Most of the time this is the extent of removing a stuck piston, but if it's still stuck it's time to bite the bullet and head to a machine shop to have the piston pressed out or, even worse, bored out.

7/10/2018 1:04:27 PM

You did not state how to do these 2 task, please explain: try rotating the engine. On larger engines you'll want to use a breaker bar to see if it will turn the engin.

6/10/2018 11:44:13 AM

Hi I have a chevey 350 that's in my race car and some one pored water in the moter the oil pan was full of wter and it was even coming out of the dip stick ive been putting diesial fuel and penetrating oil in the selenders is there anything els I can do to free it up Thanks Thomas

8/4/2015 2:17:34 PM

Hello, my name is Dave and I am in Maryland. I have acquired a rusty 1923 La France Fire truck chasis with running gear, and it has the original Wisconsin 4X5 four cylinder engine. It has been sitting in a field for years and would like to repair engine, on first inspection it appears to have broken and bent valve lift rods. Any idea where I might get some advise on repair and parts for this old dude. thanks so much. my email is Appreciate any help. v/r dave


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