Here is a photo of the the new and the old piston side by side. The new one is on the left. Some obvious differences is that the skirt on the new piston is open. Because of the height of the piston and wear of the cylinder the piston would rock in the cylinder and break the skirt off and it would fall into the engine and cause problems. There are two thin rings on the new piston compared to three wide rings on the old one. Because of ring technology the two will work as good or better than the three. Most importantly the new piston is forged instead of cast, making it much stronger. The square hole above the wrist pin whole is for weight savings. Dispite the bad photo everything else is dimensionally the same.