Briggs 5HP 130202 -Ring wear vs. bore wear

[creia]

As I believe you all know by now, I work on the old Briggs Koolbore "flatheads" from the 1960s and 1970s. These all have the aluminum bores. I commonly find significant ring wear and/or bore wear on these old engines. Generally, the bore wear will always be more than the ring wear, sometimes significantly more. That makes sense right- as the cast iron rings are harder than the softer aluminum bore?
Well, today was a first for me...
The bore was only moderately worn at .0015"(.003" is reject) while the rings were nearly worn out. I measure this by checking the ring gap with a brand new ring (it was .020"), as compared with a used ring from the engine (it was .033"). As .035" is reject, these rings are pretty much shot. In addition, the bore measurements were fairly uniform from top to bottom (no taper or out of round), and no scoring whatsoever.
Can someone explain this excessive ring wear to me? I am hoping that the ring wear explains why this engine is a smoker (mild-to moderate) upon opening the throttle?
Thank you all for any help,
Michael

[bgsengine]

I'd tend to suspect your ring wear is more due to silicates (sand) ingestion - that can embed in the softer aluminum and work like sandpaper on the piston rings. As opposed to lubrication / heat wear which the iron rings will wear/cut into the bore...

[creia]

Thank you Brian- That makes sense.
That being said, the bore does not "look" like it has anything (silica) still embedded in it, and it "feels" nice and smooth to the touch. My plan was to install a set of new chrome rings. Do you think this would be OK?
Thank you,
Michael

[bgsengine]

I'd suspect you'd be OK with chrome rings. Silicates are so small you'd have a hard time seeing or feeling them (Think of 2000 grit wet or dry sandpaper) Chrome rings being tougher would likely just glide over any embedding.

[creia]

OK understood- Thanks Brian!
Michael