I bought my 240z in 2000. It came with a L28 rebuilt from a company ATK. I replaced the L28 with a RB26 almost 4 years ago because L28 won't idle properly.
Now I'm parting out the L28. Bearings were good. All top rings are broken into pieces.
Pistons are 0.75mm oversized. The top ring groove of the No. 2 Piston is seriously damaged.
I am not going to rebuild it but what would you guess the cause of this?