Sunnen sales and application engineers like Bob Dolder get honing-related questions daily. According to Bob, here are the top three questions he gets from engine shops, followed by his typical responses:
Q: What are the best Rk, Rpk and Rvk numbers for an engine?
DOLDER: This question typically comes from our racing/performance engine customers and there is no cookie-cutter answer. The ring manufacturer's specs must be evaluated and questions regarding fuel (alcohol, methane or gasoline) and the engine block (is it race hardened, or a virgin block) must be answered. A proper evaluation of process, tooling and abrasives is then conducted, based on the specifics of each engine. Another key is access to an accurate profilometer. I always ask the customer if he has a good way to measure the bore finish...otherwise, it's a shot in the dark.
Q: What abrasives and tooling do I need to get the best ring seal?
DOLDER: This is also an "it depends" question. There are hundreds of abrasives and types of honing tools. Achieving the best seal is going to depend on the type of engine, as well as its application.
For example, a V-6 passenger car engine requires customers with diamond hones to use a 320-grit diamond stone and a 150-grit brush for plateauing. Operators should run the diamonds to size and brush for 12 seconds.
Using conventional abrasives on the same V-6 engine requires a 220-grit stone until there is 0.0003" of material to go, then finish to size with a 280-grit stone and plateau with a 400-grit for a few strokes. A 45-degree crosshatch angle is appropriate for both.