I put 3000km of street riding on one of my rd400 (wiseco pistons), ring gap went from .012" to .018 for the top ones and from .014 to .020 for the bottom ones.
It that wear normal?
Compression was and still is 120psi.
A little more than I would like to see, But ok. This can change by a few things, hone grit finish on the cylinder walls, the oil type that is assembled and run for break in and how the break in is run. Proper cleaning of the cylinders before assembly also can be a big one.
I use Sunnen hone with stones made for keyway bores which hones them to 2 tenths of a thousandths round. I like 320 grit for the thin 1mm rings.
I rub the walls with Marvel Mystery Oil on a white paper towel to be sure no grit is left in the walls after washing in a clean mineral spirits parts washer.
Assemble with synthetic oil and I use a aggressive break in of hard wide open short shift bursts after 1 heat cycle first.
Chuck
Ok thanks.