2006 Yamaha 90 4 stroke... seizure

I have just joined this forum in hopes of fixing my 2006 Yamaha 4 stroke. Have owned it for 13 years, meticulously maintained. Oil changes plug changes on time etc. Put away at the end of last season with an oil change as usual. This spring go to start and starter will not turn it over. Upon inspection found that motor is super tight...pulled plugs still super tight. upon barring the motor over with a wrench barely turns and makes a squealing noise. Any thoughts ?

Thanks, Dave

Pull the head. Inspect the cylinder walls and pistons. Paying particular attention to cylinders 3 & 4.

Presumption being you have removed the lower unit to verify the issue is within the power plant.

Thanks Boscoe,
Pulled the lower unit with great difficulty. Found the splined drive shaft to be corroded into the bottom of the power head. Also found the remains of a seal or bearing had come down the drive shaft and badly scored the drive shaft about 4 inches above the water pump housing. How do I remove the power head in order to access the area where the spline joins the bottom of the power head?

Thanks Boscoe,
Pulled the lower unit with great difficulty. Found the splined drive shaft to be corroded into the bottom of the power head. Also found the remains of a seal or bearing had come down the drive shaft and badly scored the drive shaft about 4 inches above the water pump housing. How do I remove the power head in order to access the area where the spline joins the bottom of the power head?
Also, the power head turns fine without the lower unit attached.

I am working with Chid69 on the engine and am trying to attach photos of the rubber seal that showed up on the driveshaft after the lower unit was FINALLY removed. Cannot tell if the photos are going to appear. I'm better with a wrench than a computer.

If the photos are visible, they would show what appears as the circular remnant of a rubber seal from "who knows where "up high at the top of the driveshaft. Can't figure out where this black/gray seal might have come from, but it is around the driveshaft and slid all the way down to the water pump housing when the lower unit was removed. I don't know what sort of bearing seal it might be (other than possibly one around the splined receiving hole at the bottom of the power head/engine ???) The spline itself, other than getting dusty from "aluminum rust" on the way out , was NOT really very corroded and still had a good bit of moly grease on it, and NO rust.

We are baffled by what this "seal" might be and where it came from.

Any comments are welcome.

Factotum

The drive shaft goes through and rotates the oil pump. Quite likely that you are seeing the oil pump seal.

Why are you doing surgery on the motor without having the service manual handy?

Snippet from the parts catalog below: