From what I've seen different ring manufacturers recommend anywhere from 240 to 400 grit. Hastings Piston Rings recommends 220 - 280 grit for all 3 ring types (cast iron, moly, or chrome)

Cylinder bore refinishing

 

Here's some info from EngineHones.com: Technical information on using engine hones, flex-hones, ball hones

 

thanks guys looks like i was right on the 320-400 grit, its just been so long since ive done this type of repiar i wanted to be sure . my main concern was using to coarse of a flex hone and making the bore to large and having to loose of a piston to wall clearance

 

You would wear your arms out before you could remove enough material with a flex-hone to make the bore oversize!

 

Agreed, FlexHone CAN'T remove an appreciable amount of material, nor will it change the "shape" of the hole.

It is highly recommended, unless the cylinders are rebored, to use a "power hone" or "rigid hone" for moly rings. Molys have a hard time "seating" in bores that aren't "round". ANY taper or out-of-round will inhibit that. Iron rings are recommended if not reboring.

We use a Sunnen "625" stone for most moly applications. Higher level "race" engines get 820 and a "plateau" hone. Iron rings get "525". I don't think these numbers represent the actual "grit", but those are Sunnen's numbers. NOBODY knows more about "honing" than Sunnen... -

Jim

 

bores have been checked and are not out of round so should be ok, would really hate to pout cast iron rings back in this thing as they break way to easy in a forced induction engine

 

We've successfully used plasma-moly "file-fits" when things vary ever so slightly. You can "plate-hone" it again and have a tad more piston-to-wall without really hurting anything. Set the gaps accordingly and as long as you don't get TOO crazy with clearance, it'll be fine. Adding a graphite coating to the piston can add about .0005". Even in a "budget build", wall finish and ring prep are just about the most important aspect of a "blown" application.

You didn't say which V6. 3.1? 3.4? 3.8?

Jim

 

hone

with the moly rings, you want a smooth cylinder. I use a sheet of 600 wet or dry sandpaper wrapped around the stones of the hone.(the 3-legged type). I put the oiled sandpaper in the cylinder, then put the hone inside of the paper. anything coarser will chew the moly off. Lets face it, a ring job is not a lasting solution, although I have done it many times and works fine. Check the top ring gap at the very top of it's travel in the cylinder. If too wide, it'e going to have some blow-by. I had my own engine rebuilding shop for several years. and am just sharing what I learned.:spank: