Sunnen SV-620

The SV-310 handles bore diameters of 25–200 mm and workpieces up to 500 mm tall — covering passenger car engine cylinders, transmission bores, and medium hydraulic cylinders. The SV-620 extends the diameter range to 50–450 mm and workpiece height to 1,200 mm, targeting heavy-duty diesel engine cylinder bores, large connecting rod big-end bores, and large-diameter hydraulic cylinders. The SV-620 has a heavier spindle drive, longer stroke mechanism, and higher workpiece weight capacity (1,500 kg vs. the SV-310's lighter capacity). For shops that need both ranges, the SV-620's lower end (50–200 mm) overlaps with the SV-310, but the SV-310 provides more economical coverage for the smaller bore range.

Diesel engine cylinder bores in cast iron blocks typically use silicon carbide (SiC) honing stones for roughing (80–120 grit) followed by aluminum oxide (Al2O3) or SiC for sizing (220–320 grit) and plateau honing (400–600 grit). The final plateau honing step produces the desired crosshatch angle (typically 45–60 degrees to the bore axis) with flat plateaus (Rp < 0.2 µm) and oil-retaining valleys (Rvk 0.5–1.5 µm) for piston ring seating. Sunnen supplies the complete stone specification for each application — block material, bore diameter, target surface texture parameters — from its application database covering thousands of engine families.

Connecting rod big-end bore honing typically follows a bore-resizing operation (grinding the cap and rod mating surfaces then reassembling to bore the round big-end hole). The honed bore receives a press-fit or slip-fit bearing shell and must meet tight roundness (< 0.005 mm), cylindricity, and surface finish (Ra 0.4–0.8 µm crosshatch) specifications. On the SV-620, connecting rods are fixtured vertically in a work-holding plate that allows the rod to be presented to the honing spindle at the correct angle. Small-end bores (for pin bushings) are honed in the same setup after a fixture change — the small-end bore typically targets Ra 0.4–0.8 µm and close dimensional tolerance for interference fit with the pin bushing.

Plateau honing is a two-step surface finish process: first, a relatively coarse honing step (80–220 grit) produces the crosshatch pattern and corrects bore geometry; second, a short plateau honing step (400–600 grit, minimum strokes) removes the surface peaks (the 'peaks' of the Ra profile) without removing the valleys. The result is a Rk surface profile with a flat plateau (Rk 0.3–0.6 µm), shallow oil-retaining valleys (Rvk 0.5–1.5 µm), and minimal peaks (Rpk < 0.1 µm). This surface supports the piston rings during break-in (rings wear against the flat plateaus until fully seated) while the valleys store oil at the ring interface. Diesel engines without plateau honing take longer to break in and may consume more oil during the break-in period.

Yes. Hydraulic cylinder bores require Ra 0.2–0.8 µm crosshatch surface finish for dynamic piston seal compatibility — smoother than that and the seal may not receive adequate lubrication from the hydraulic fluid; rougher and the seal wears rapidly. The SV-620 produces Ra 0.1–1.6 µm across the full bore diameter range, covering the hydraulic cylinder specification. Bore roundness (< 0.002 mm) and cylindricity (taper < 0.005 mm over bore length) are critical for seal performance — out-of-round bores cause piston seal breathing (seal edge loading varies by rotation angle), leading to seal wear and cylinder leakage. The SV-620's vertical configuration and active gauging provide the geometry control required for hydraulic cylinder bore finishing.