I have a johnson gt 200 that is locking up right before it did heard a rattling like marbels in a can not a knock ..got home took out plugs and took socket and could turn crank with some resistance i was look over it and at base of engine near where engine rotates were 3 loose bolts and inside so part that is rattling around when you put finger in crack..what is this and what should i do next to repair it myself..thxs

I wouldn't even begin to guess what to do other than take it to a mechanic.

Basbandit is right.  Take it to a good mechanic, preferably a dealer--lest you end up spending more money than you ever thought.  Twice I have had to cancel out of tournament because of bad gas.  Good-bye carburetors.  The old timers use to say that a ounce of prevention was worth a pound of cure.  When it comes to motors on your boat nothing is more true.  Each day you wait is another good day of fishing GONE!  Good luck.  Hope it is not too serious!  Uncle Tom