Honing Definition said:Honing is a final finishing operation conducted on a surface, typically of an inside cylinder, such as of an automotive engine block. Abrasive stones are used to remove minute amounts of material in order to tighten the tolerance on cylindricity. Honing is a surface finish operation, not a gross geometry-modifying operation. Hones can be of the multiple pedal type or the brush type. Either type applies a slight, uniform pressure to a light abrasive that wipes over the entire surface.
Cylinder Wall Honing Prep Considerations for Good Piston Ring Seal
Regardless of the type of ring facing that's used, the proper bore finish is required for a good initial seal. Most aftermarket ring manufacturers say the bore finish should be less than 20 RA, with some recommending 14 to 18 RA as the "ideal" range.
"To achieve the proper cylinder bore finish, rebuilders need measuring equipment that can measure more than just RA," said Wilkinson. "They also need to measure RVK, RK and RPK."
RA is the roughness average and should be .25 to .50 microns or less, according to Wilkinson. RVK is the average depth of the valleys and should be .75 to 1.50 microns. RK is the average roughness of the core, and should be .63 to 1.25 microns. PRK is the average height of the peaks, and should be .25 to .50 microns.
To achieve these kinds of numbers, various honing processes may be required depending on the type of rings used. Scott Gabrielson, ring design engineer for Federal-Mogul, says for moly rings, he recommends a two-stage honing process: honing the bores with a #220 or #280 grit stone to within .0005" of final size, then polishing the bores with a #400 grit stone or flexible abrasive brush to plateau the surface.
This procedure can produce a bore surface with plenty of bearing area to support the rings, adequate crosshatch to hold oil for ring lubrication, and no sharp peaks to wear the new rings. A plateau finish also provides an instant seal to minimize blowby and ring break-in.
For chrome or nitrided ring sets, Gabrielson says the cylinder bores can be finished with a single stage process using #220 or #280 grit stones. For these applications, he does not recommend plateauing but he does say the stones should be run a little longer at reduced load to finish the bores.