I have an example of the damage you can do trying to press a piston on a rod with a shop press. A customer brought a piston and rod he had tried to install to the shop where I work. He had mannaged to gall the pin in the rod and it cocked slightly when it went into the piston on the other side, this pushed an wad of alumium up on one side of the pin bore. He wanted us to finish putting it on. He ended up having to get a new piston and rod because of the damage. Let an automotive machine shop do it you'll be better off in the long run.
Sean
