Small Engines (Lawn Mowers, etc.): clunk, metal noise, mower deck

Question
I have had a clunking noise in my lawnmower that was accompanied by smoke - it always went away last year but I used my mower once this year and it started clunking again (metal on metal sound)and now won't start.  It seems to be there when it first starts up but just for a few seconds then when the mower is hot, it gets bad. there is clean oil and gas in it.  don't know whether it is worth the cost of repair.  Its just a 5.5 craftsman - 6 to 7 years old.

Answer
If you hear a metal-to-metal sound when you rotate the engine (even if it doesn't start), you may want to check to see if the crank or blade is bent.  This may be causing the blade to be contacting a stationary area of the mower deck.  The only other metal-to-metal noise I can think of is if the flywheel key is badly sheared and the flywheel is "flopping" around on the end of the crank (this will also cause it to not run).  Hope this helps.