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.

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.

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

5/27/2015 7:21:19 PM

The best penetrating oil is the cheapest. 1 part transmission fluid, 1 part acetone. shake the mixture. If you suspect varnish stuck rings, ethanol based fuel treatments or denatured alcohol work well to dissolve varnish instantly. I use the grease gun method for removing fast stuck pistons. I have a spark plug base welded closed with a drilled and tapped hole for a Zerk fitting. I fill the cylinder with old used motor oil, screw in the "Zerk plug" and pump grease into the cylinder. This will almost always work, but be careful of thin cylinder heads.

11/24/2014 5:04:02 AM

Its best answer is available on

10/28/2014 11:04:14 AM

When confronted with a seized piston on a 15 hp Faibanks-Maorse hit & miss my dad did something he never had done before. He bought a 6-pack of Coca-Cola. Gave the engine 2 bottles and he & his brother drank the remaining. Strongest drink prior to that was lemonaid. It was not long before the piston was free, and Dad had the engine running after over 35 years of rest.

12/31/2013 10:55:07 AM

If hammering the stuck piston via a piece of wood doesn't work, here's another way to move it in the cylinder. 1. Cut several discs of varying thickness wood about 1/2 inch smaller diameter than the cylinder. 2. Put enough discs in the cylinder to exceed the height of the top edge. 3. Tighten down the cylinder head to press down on the wooden discs. The discs will compress, and the piston should move. 4. Remove the cylinder head and add more discs to get the piston pushed down further. It worked for me.

Dave Yost
4/1/2012 6:34:53 AM

I had such a problem with a small, single cylinder marine steam engine. Carelessness had allowed the piston to freeze in the cylinder. 10¢ worth of oil would have prevented it. Oh well. The piston was frozen in there pretty good. I took a square block that extended above the cylinder and gave it a few whacks. This seemed like a really bad idea as the force was being directed mostly toward the center of the piston. I was not sure the relatively thin steam piston could handle the force. Then I got my brainstorm. I bought some ABS (PBS? whatever) irrigation pipe. ’stuff is cheap. I bought a diameter that was just a tiny bit smaller than the cylinder. I cut the plastic pipe so it stuck out of the cylinder a couple of inches when it was sitting on the piston.After a week of Kroil soaking, I put the plastic tube into the cylinder. I put a 2x4 block on top of the plastic, and then gave it a whack with a mallet. It easily started moving and was completely free in about four whacks. The idea here was to concentrate the force of the pounding right at the outert edges of the piston. This way, the piston itself is not subject to the force of the pounding; only it’s outer edge. No damage to the piston at all.