Here are some pics of the spare piston that came with the 400 stuff. Some are ready to use, some need skirt work n a window. You can see the longer skirt on the one side of the YZ490 piston. Now, what the factory did to keep the "balance" of the pison on the rod was move the wrist pin hole off center. When we remove part of the long skirt(to keep it from bottoming out in the 350 bottom end, 350s shorter rod), it becomes heavier on one side. I ran it like that for a while in my Leckich but after about a year, it started pinching the alum wall onto the ring/ring groove(sticking ring)...had to open it back up. Kinda worried about the weight unbalance at high rpms. The next piston I cut the skirt off of, I tried to figure the rough amount of material removed then remove that much from the other (arched) side. That was 3 years plus ago and so far no issues...knock on wood. I will be pulling the Leckich
Engine soon for another inspection...and probably swap in a Briggs setup to try some trial runs.
Just thought you may want to know about the balance/wrist pin issue and what I am trying to compensate for it. Any other ideas are appreciated.
Gary
you know you got me thinking and I measured the piston up and the wrist pin is in the center of the piston