cr 125 piston seized!!!

[rev440 man]

I have a 1987 cr 125r and the piston is seized to the cylinderwall. now how do i unseizes the pistion so i can rebuild it. Is there a way to do it without taking the motor out? Is there somthing i can put on the pistion that will eat away the rust?? It is seized from sitting out side for two years with no plug in it. not mutch rust around the pistion, hardly any. Any help would be greatly appreciated .
Thanks
Alex

 

[Mike270412]

Fill cylinder with diesel fuel or penetrating oil and let it sit for a few days.

 

[rev440 man]

ok thanks. And also I need to no how tight to torque the head bolts and what the compression should be.
thanks
Alex