what happens if your motor locks up

Check your oil first. Water in the crankcase can cause hydrostatic lock if you submerged the intake or breather. Drain the oil and see if it's milky. Also, try turning the flywheel by hand with a wrench. If it moves, the starter might be jammed.

Most likely a seized piston from overheating. Did you ride hard before the creek? If the cooling system was low or the fan failed, that could cause it. Pull the spark plug and see if you can turn the engine with a breaker bar on the crank bolt.

Could also be a broken connecting rod or bent valves if it dropped a valve. That's rare but happens. Listen for any knocking before it locked? If not, I'd suspect water ingestion first, especially since you were in a creek.

Before you tear into it, check the starter itself. Sometimes the starter gear gets stuck engaged. Unplug the starter and try turning the engine by hand. If it turns freely, the starter is the issue. Easy fix if that's the case.

I had a buddy with a locked up engine from a failed cam chain tensioner. The chain jumped and jammed the valves into the piston. That required a complete top-end rebuild. Check if the timing marks align before trying to force anything.

Don't force it with a breaker bar until you rule out hydro lock. If there's water in the cylinder, you'll bend the rod. Drain the oil, remove the plug, and crank it slowly with the starter. If water shoots out, you'll know.

Sounds like you might have hydrolocked from the creek. Even if the intake wasn't submerged, water can splash into the airbox. Check your air filter for water. If it's wet, that's likely. Let it dry out and change oil before attempting to start again.

Another possibility is the transmission lock up. If the belt broke or a clutch spring let go, it can jam the engine. Try shifting into neutral and see if you can rock the ATV. If the wheels turn, it's likely the transmission.

I disagree with the transmission idea. A locked engine that won't turn over at all is almost always internal engine damage, not drivetrain. Drivetrain issues usually let the engine spin freely but not move the ATV. Check the crankcase for metallic debris.

Could be a seized oil pump. If that fails, the engine overheats rapidly and locks. You might see signs of extreme heat on the cylinder head. Check the oil pressure switch if you have one. No oil flow equals instant death for the engine.

Before you go deep, check the simple stuff like the kill switch or wiring short. But if you say the pull start is also stuck, that rules out electrical. You've got a mechanical lock. Time to pull the valve cover and look for damage.

Make sure the engine isn't just stuck from sitting. If it cooled down after hydro lock, sometimes the water expands as it freezes. No, that's only in winter. But you mentioned a creek, so maybe mud got into the starter bendix? Clean it out.

I've seen a locked motor caused by a seized camshaft bearing. No warning, just sudden lockup. The engine wouldn't turn by hand. Had to replace the head. Check for any play or heat marks on the cam caps. That could be your issue.

You might have dropped a valve seat. That's common on some models if the engine gets too hot. The seat falls out and jams the valve open against the piston. You'll need to remove the head to confirm. Start saving for parts.

If you haven't already, check the ground connection on the starter. A bad ground can mimic a lock because the starter won't have enough power to turn, but the engine might still spin freely by hand. Use a wrench on the crank pulley.

I think it's likely a simple piston seizure from low oil. Did you check your oil level before the ride? Even a slightly low level can cause heat buildup in a high load situation like crossing water with resistance. Change your habits.

Don't rule out a broken ring that wedged into a port. That can lock the engine solid. You'll need a bore scope to see inside the cylinder. If you see scoring, it's time for a rebuild. You might get away with a hone and new piston.

One more thing: check the exhaust for blockage. If a mud dauber or critter built a nest in the pipe, it can cause back pressure that leads to a seized piston. You'd need to remove the pipe and inspect. Unlikely but possible.

For now, just drain the oil and look for metal flakes. If you see gold or silver specks, that's bearing material. Dark grey is aluminum from pistons. Either way, you're looking at a teardown. Might as well pull the engine and take it to a shop.

I had a similar thing happen on a Honda Rincon after crossing a deep puddle. Turned out the CDI box got wet and shorted, causing the engine to lock up electronically. Dry everything out and recheck. But if the pull start is stuck, it's mechanical.