Small Engines (Lawn Mowers, etc.): Pull Cord on Lawn Mower Stuck, piston ring, internal failures

Question
I removed the rewind starter and tested it and it is not stuck.  The flywheel is hard to turn by hand.

What might be my problem and is there anything I can do. Craftsman 6.0 Lawn Mower.Mod. # 917.376290. No repairs have been done to this mower.

Thank you.

Answer
Hi Merv,

I noticed a follow-up question that you put in the comments section at AllExperts but due to the space limits there, I was unable to see all of your question.  Could you please re-ask it again?
http://www.allexperts.com/postQuestion.asp?Expert=107&Category=1746

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Last answer:

Not a good sign.  With the spark plug out and blade un-obstructed, if the engine turns hard all through its revolution, it is seized.  Due to a lack of oil, a bad oil flow internally, a broken piston ring or other internal failures.  If you hit an object while mowing, the flywheel key might have sheared but then the engine would tend to "kick back" and only be hard to rotate while the spark plug fires.

Let me know what you find.
Michael