I'm trying to install an Athena big bore kit on a 2002 Suzuki DRZ400e. I'm installing the new piston, and i'm having trouble getting one of the circlips to fully seat. To me it seems/looks like the piston pin is slightly to long, stopping the clip.
I had the same issue with the 150 kit on my TTR125. It took a little persuasion with a small flat tipped screwdriver to get it seated. It seemed like a bit too much force needed, but it finally seated in the groove. Just be careful you don't slip and score any of your metal parts, or worse, puncture your hand!