Small Engines (Lawn Mowers, etc.): 16.5 briggs stratton engine, briggs stratton engine, briggs stratton

Question
i have acraftsman mower model no. 917.271630 bolt holding main pulley on engine broke had to be removed with an easy out.after replaced mower gets black dust all over engine under hood on front wheels all over the deck looks like carbon.repair shop can not find anything wrong.they say it could be comming from lawn.it happens on 2 lawns i do. do you have any answers.friend said it might be blown head gasket.thanks for your help

Answer
I haven't ever had a head gasket blow on that engine, but it is possible.  Briggs showed us several engines that had loose head bolts and the symptoms/damage it causes to the engine.

It wouldn't hurt to use a cylinder leak down tester to see if the head gasket is leaking.

Did you replace the pulley?  The pulley keyway may be damaged enough that it is actually grinding the inside of the pulley and/or the crankshaft.  I'm sure a pulley is much cheaper than a new crankshaft.  If the pulley was damaged you could be seeing black belt dust.  I would check both belt for signs of recent wear.
Let me know what you find.
Eric