John Deere L110 with Kohler 17.5hp not turning over

[gymtebro]

The mower:

• John Deere L110
• Kohler 17.5hp (CV491s)
• Been sitting outside for 7-8 years
• Replaced battery, spark plug, and carburetor which had it was running and cutting

The issue:

• The mower will not turn over now (a couple days after it was running and cutting)

Relevant information:

• Replaced spindle assemblies and it won't turn over after putting the deck back together
• Replaced the air filter when replacing the spindle assemblies
• The starting solenoid seems to be good
• I have replaced the starter in an attempt to fix the issue to no avail
• I have also added some oil and it may be a hair on the full side
• When I turn the ignition, it attempts to turn over and even turns the flywheel about half a rotation on occasion before stopping. If I continue to turn the ignition, nothing happens.
• The flywheel is difficult to turn by hand and is rusty (just surface rust, no major pitting)
• When turning the flywheel by hand, I can hear some grinding/squealing
• If I remove the spark plug when turning the flywheel, I don't see any oil coming out of the hole
• I have a fuel pump and fuel filter on hand but I don't believe those are the issue
• There is some debris in the fuel tank

Did I put something back together incorrectly? Is this a poorly timed seized engine? I'm at a loss here and I'm having a hard time describing this issue well enough to get relevant Google results.

I am willing to answer any questions, provide any additional information, or take some pictures/videos as needed.

 

[gymtebro]

Added a video of me manually turning the flywheel https://youtube.com/shorts/KeTIoYha_0g?feature=share

 

[bertsmobile1]

The automatic decompressor may have failed
The big end or little end may have siezed .
If it was me, the first step is to remove the flywheel & check for debris inside jambing the alternator.
Then drain the oil & check for stuff that should not be there
After that it is pull the engine apart.
A piston or con rod is a cheap fix
a new short block is an expensive fix .

 

[Scrubcadet10]

is the flywheel easier to turn with the spark plug out?

 

[gymtebro]

The automatic decompressor may have failed
The big end or little end may have siezed .
If it was me, the first step is to remove the flywheel & check for debris inside jambing the alternator.
Then drain the oil & check for stuff that should not be there
After that it is pull the engine apart.
A piston or con rod is a cheap fix
a new short block is an expensive fix .

I will start there. Thank you for the advice! I'll let you know how it goes!

 

[gymtebro]

is the flywheel easier to turn with the spark plug out?

It doesn't feel like there's any difference. That video I posted was with the plug out

 

[gymtebro]

I took the cylinder head off and the flywheel is now turning freely. I see a fair amount of carbon buildup on the piston and valves but I don’t see any reason why they would grind or be locked up. The rods, rockers, and springs all seem to be fine. Here are some pictures of it disassembled.

https://imgur.com/a/wjxO3jf