I have a Koyker 140 FEL that I am trying to replace a piston in one of the hydraulic cylinders. I was only able to remove the old piston by unscrewing it over the threaded portion using a pipe wrench. When I tried to install the new piston I ran into same problem. The only way to get it started on is to screw its onto the threads on the end. The shaft cuts threads into the aluminum piston but was not able to get it all the way on. I ended up ruining the new piston also. Any idea how to get the piston over the end of the shaft? Will cooling the shaft cause it to contract enough to make the piston fit?