Originally Posted by kfree
I pulled the head and rocked the bike back and forth and noted the piston was frozen so I sprayed some wd40. I rocked it again and it moves freely now.
With the spark plug out the motor turns freely when I let out the clutch. With the plug in, it doesn't seems to turn at all.
Any thoughts? Thanks in advance.
If the plug is stopping it from moving, it's just compression, and is normal. When you pulled the head the piston may take the jug with it, it is a tight fit, however holding the jug down would be more than enough force to allow the piston to slide up and down. If the piston is seized, then it wont move at all, I dont know how people have replaced the top end in this case, but I dont think that's you're issue. If the piston was jammed in the cylinder, you may not have enough oil in your gas, or you may be running too lean.