I have been attempting to unseize the pistons in my 1971 Honda an600. I have tried many methods with no avail, such as wd-40, motor oil and diesel fuel to try to coax the pistons into moving. I have been tapping the top of the exposed pistons with a block a wood and a hammer and no movement. I heard that using phosphoric acid could break up the material between the pistons and the cylinder wall. However I am afraid that the acid could damage the engine. Any thoughts on this?