Originally Posted by y2k600f4
I have read that Moly and Plasma-Moly top compression rings need a final hone that is fine; around 600 grit. However Hastings recommends 280 grit (talked to tech support). Also from their documentation"
Anybody know why the difference in recommended roughness ? 600 vs 280 is a significant difference. Is is just Hasting that recommends this. I just want to confirm the correct hone for my application. I beleive they are Hastings Powerflex rings. Thanks.
Different ring finishes (chrome, moly, plain) prefer different wall finishes. Chrome will tolerate and needs a course finish to assist break in of the surfaces. A raw iron ring also like a rough finish but for a different reason which is more oil retention in the wall. The chrome ring doesn't need so much oil on the wall but needs to shape the wall to its contours.
Moly prefers a smoother wall to prevent early wearing of the coating. Moly lke chrome doesn't need as much upper cylinder lube but gets there by supplying its own slipperiness where chrome is simply resistant to wear in a low lubrication environment.
However super smooth walls as you get with a 600 finish tends to be too smooth, the current thinking is what's called plateau honing which combines both rough and smooth features. This process first puts a 250-300 finish on the wall then comes back with a 400-600 stone to break the rough edges of the first coarser cut. This provides both more oil retention in the coarse hatch for the lower rings and the thrust skirt with a smoother surface from the finer hatch that the moly ring likes.