So u built up the case with a Dr kit right ? So before the cylinder was slipped over the piston to build it all up , it's been said by many that one should carefully slip the rings off the piston or better yet if packaged separately, slip the ring into the bore of the cylinder. Now for a 45mm bore ( Dr I think ) the space between the two little ends of the ring ( there are several variations on the end and how they relate to their respective centering pin that has been carefully we hope placed along the groove that the ring lives at ( don't put wrong ring in wrong ringway ) the gap between the two ends should be 0.18mm NOT INCHES. IF U NEED THAT conversion let me know and I will look it up. Gentle filing if less is necessary for the simple reason that metal expands when hot. If the ends expand and kiss each other the ring will now gap out of it's little home. And the ring will accumulate even more heat until it decides to be come a welding stick and attach itself to the cylinder ....soft seize?? Hard seize....??? That's all I know. Sort of.