Does this sound like a seized lawn tractor?

My Brother in Law has a typical lawn tractor (I forget the make and horsepower).

He put 2 stroke oil in it and now it wont start. At first he thought it was the battery, so he replaced that.

I went over to take a look at it. When I turn the key, I can hear the engine try to turn, and maybe turns a degree or so and that’s it. Like all lawn tractor engines, the top of the engine has a honeycomb grill with the flywheel(?) under it. I can see that flywheel turn just a hair when I try to start it.

So, my assumption is that the battery is fine, since it is new and I can see the engine turn a little. My best guess is that the 2 stroke oil seized the engine, but I’m not sure. Or, is there something else I can check? If I can see the engine turn just a bit, then I asume the starter and everything leading up to it is fine.

Any ideas/advice would be very appreciated.

do you mean he put two-stroke oil in the crankcase, or in the fuel? If the crankcase, how long was it run like that?

In the crankcase. I’m not sure how long he ran it.

Grab the fly wheel and try to spin it.

yeah, I suppose it’s possible. you/he might want to first pull the spark plug and make sure by some freak coincidence the cylinder’s not full of something and hydrolocked.

Supposing the cylinder is dry, can you think of anything that would cause the symptoms I described? I honestly don’t even know where to look.

Can using 2 stroke oil in a 4 stroke engine even seize it? I figure 2 stroke oil is thinner, but in something like a tractor, I can’t really see it seizing the engine, unless used hard for a long, long time.

Is there any oil left in the crankcase? If not, uh-oh.

The 2 stroke oil was drained and refilled with proper 4 stroke oil.

Disconnect the sparkplug(s). You don’t want it to start unexpectedly.

Try to turn the engine by hand. If you can’t get to the the flywheel on top, there should be a big pulley under the engine. Try to turn it. That should tell the story.

Pull the plug and then hit the key.If it still resists turning over check for something binding up the output belts/blades/wheels etc. If everything looks free and clear then I would try the flywheel.
I wouldn’t rule out the battery or the starter just yet.

Thanks. I’ll give that a shot.