We’re seeing OEM drawings for 2025 small-blocks calling ±0.0002 in on wrist-pin bores and 8 µin Ra, which had me reworking dwell and feed on the Sunnen SV-15 this morning. Anyone else getting these revisions, and if so are you holding it with a CBN finish-hone or switching to finer diamond sticks?
We’re hitting ±0.0002 and “8 µin Ra” on an SV-15 with 1200-grit diamond, dropping stone load about 15% for the last 0.0001–0.00015 and a quick 10 s nylon-brush plateau, but only if the oil holds about 68°F. CBN didn’t beat diamond on forged rods here; it helped on PM where we saw torn metal — what are your rods, and do you have in-process air gaging on the pin bores?
Locking the SV-15 oil at 68°F and letting the parts soak 5–7 minutes before the finish pass is what got me to “±0.0002” and “8 µin Ra” reliably — the last tenth was just thermal drift. If you’re in aluminum pin bosses I’d stick with fine diamond; CBN left a slight smear for me. Are you running the chiller or gauging at ambient?
I only got it to settle down after adding 5 µm filtration to the SV-15 tank — clean oil kept the stones from loading and a light “CBN” finish pass hit the spec without extra dwell. If you’re still on diamond, try the filter swap first; did you stick with the stock screen or go finer?
On my SV-15, the real win was swapping to vitrified 1500‑grit and a shoe‑backed head to hold roundness, then a short ‘size‑lock’ spark‑out so the servo quit chasing size — this creep in prints drives me nuts. If those wrist‑pin bores are bronze‑bushed, resin diamonds glaze and lie about finish; try vitrified and deburr any oil slots before the last pass. @ella2190 did you see glaze issues or are yours parent metal?