Engine Popped, now wont start

[mrlmd1]

DV - How do you know that? Did your mechanic take it apart already? If not, make sure you are there when the he removes the plug, or take it out yourself and see what he put in if he changed it.. If the plug was too long, it would hit the piston and the rebuild is on him.
Why were these gaskets replaced? You didn't answer alantf if it was leaking oil.
How long have you had this bike? Did the previous owner do that (change the plug) just before you got it? If that's the case, you may be screwed with the cost of a rebuild unless you can go after him.