Topic: first build: 1973 CB750 with spare motors and parts

[pdcarpen]

I just bought a project bike and now have started the teardown.  The previous own did some work that I am now going behind to figure out what was done.  The motor would turn over when I got it but it would not run.  I was able to get it running but it was backfiring at about 2500 rpms.  I have now taken the motor out and taken the top off.  Cylinder #2 had a broken ring and scratched the piston wall.  He did put new pistons ring on but not sure how the rings got broken.  I will be asking for help as I know very little about this stuff.  I took on the project to keep me busy after work each night and really wanted a challenge.  I am really excited about his build and hope I will be able to get support when I need it.  I will try to post pictures to give you an idea of what stage I am at. 

[pdcarpen]

The #2 cylinder has broken rings.  I am not sure how that happened but it did scratch the piston wall.  I would like to buy a set of new rings and just be done but I am not sure what part # to order.  The pistons in the motor have a different gap for the rings than the two extra sets I have?  The two extra sets have a smaller gap for the rings than the ones in the motor.  I wanted to keep the cost of this build low so I made sure I found the deal with a lot of extra parts to work with.  All of the piston are 61mm but ring gap is different?  What am I missing?  Thanks again