Small Engines (Lawn Mowers, etc.): engine smokes after blade hit an object, crankcase oil, lawn rake

Question
Hi John,
I have a 15.5 hp craftsman tractor with hydrostatic drive(model 917.270622/ engine 28u707). The tractor was driven over a lawn rake which stopped the engine instantly.  I now get a white/blue smoke out of the mower (exhaust).  It actually starts and runs fine but I am afraid to run it for more than a few minutes.  I suspected the problem to be bent blades and replaced them.  I then removed the deck and drive pulley (key was definately worn) and ran just the engine not hooked up to the drive train (still smokes).  Could this be a broken ring?  I removed the valve assembly (ohv) and handcranked the motor to find what looks like a potential line on the cylinder while the piston is moving (not a scoring).  If this is a ring problem can I replace them with my own (I am not a mechanic) tools? I use to replace the rings in my old honda elsinore (30 yrs ago) but I can't see how to do it on this motor.
Any help would be appreciated.
Thank You

Answer
 Hello Jay:

 You can View a Breakdown of the Engine at this Addy http://shop.briggsandstratton.com/BShopProductListingPage.asp?rsvp=0&PARENTID=0&... and Enter the Model Numbers 28U707 and the Type Numbers 1174 and Click Search. On the Next Page Scroll Down to the 2nd Listing and Click on View PDF. Clean the Crankcase Vent Before you Disassemble the Engine. Does the Crankcase Oil have a Gas Smell to it? Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. I enjoy knowing the Outcome. Thanks.

 Good Luck

 Respectfully

 John