I had to remove the engine because I learned that bolts have a flange (not sure if about the right name) on the low position. This made it impossible to remove it (sorry for the crappy pic).
Then, I remove the engine and found valves are dirty
piston same as valves
Also I found a hole in the cylinder head (upper right side). Probably, this is affecting the performance of the engine and don´t know if the hole must be fixed.
Finally, I went to the shop asking about rebor and the machinist said yes but will do it until next Monday due to holidays.
Feedback is welcome.