In the past, we’ve discussed that different piston rings and different use applications all like slightly different honing techniques. While most builds will probably be fairly forgiving of a hone with numbers a little more in one direction than the other, NHRA Pro Stock does not fall under that umbrella. So, when you have someone like Greg Anderson — the winningest Pro Stock diver of all time — machining a block, your tolerances are tight and your numbers exact.
Modern piston rings are a different animal than the rings of even a decade or two ago. Besides that, our understanding of what is actually happening on and in the walls of the cylinder is more advanced than it has ever been before. So it stands to reason that today’s processes and methods are different — and measurably better — than they were just a couple of short decades ago. KB Racing’s Anderson, along with Total Seal’s Lake Speed, Jr., walk through the process of honing a block for a modern ring package.
Making a Round Hole
“The first key is to make the cylinder round,” says Anderson. There are two key components to doing that: a quality honing machine, like the Rottler H85AX Anderson uses, and using a torque plate on the block. “If you were to hone this block without a torque plate and then go bolt your cylinder head on, the bore will be a completely different shape,” Anderson explains.
The torque plate is a cylinder head analog, with clearance to access the cylinder bore through the center of the plate. By using the same cylinder head fasteners as you will in the engine, tightened to the same torque, you are putting all of the stresses into the block that will be present when the engine is assembled, and then making sure you create a round, straight bore.
The first step in preparing a modern cylinder finish is using a modern abrasive. “We use a 170-to-200-grit diamond cutting stone,” explains Anderson. We’re looking for a certain depth of the groove, basically, the Rvk.” You might recognize the term “Rvk” from some of our other articles on honing; it’s the “valley depth” measurement of the cylinder finish, as measured by a profilometer, in microinches.
“That valley will hold the oil behind (or below) the surface the ring is riding on,” says Anderson. “As we found over time, we need that groove to be slightly deep, because without oil, you’re in trouble. Years ago, everyone liked to hone the cylinder very very fine. The thinking there was that reducing friction was everything. The problem is, with that fine finish, you ran out of oil on the surface, and then you were back into a high-friction scenario.”
The Modern Plateau
The idea of plateau honing is fairly self-explanatory — once you have created the deep valley you have similarly tall peaks. Those peaks would be quite abrasive on the rings. So the idea is to knock the peaks down without touching the valleys. “We’re going to plateau over it with a 600-grit CBN hone,” Anderson explains. “CBN” or Cubic Boron Nitride is a modern abrasive that is both extremely hard and extremely durable. It is able to cut cleanly and rapidly, offering minimal heat buildup with a great finish.
By knocking the tops of the peaks off, but retaining the valleys, you create a nice, low-friction surface that also has the ability to effectively hold oil. “The surface the ring rides against is nice and smooth, with low friction, but you still have increased oil capacity,” says Anderson. And with a modern abrasive like CBN, you’re getting a final finish in fewer strokes of the machine, which has both quality and productivity advantages.
“Now, we go to within a tenth of a thousandth of finished size with the diamond hone, then you go to your 600-grit finishing CBN, and you really aren’t taking any extra material off,” says Anderson of the process. “Back in the day, people would get within a thousandth of target and start taking two or three tenths off with this stone, and then two or three tenths off with that stone — the whole time taking away their valley. If you are progressively finishing the bore, you’re completely doing away with your valley.”
Speed agrees, saying, “The old plateau method was to hone with 320 grit to size, and then 400-grit to finish. Your cylinder walls really wouldn’t be able to hold enough oil. But, because the old rings were Moly based, they were porous, and they held the oil themselves, so they allowed you to do that.” The modern materials used in today’s advanced rings, no longer mask the shortcomings of the old honing methodology.
“Today’s rings have a very hard coating on them and you’re really not going to wear the ring much. It’s a very very flat surface, and nowhere to hold the oil in the ring, so [the oil] has to be held in by the block,” Anderson sums up. At one point in time, the battle was between piston ring manufacturers and piston manufacturers to see who could make a more precise product. Now, the challenge is how to make a perfect cylinder surface for these advanced piston rings every time. Thanks to modern materials and methodology, it’s not only achievable, but repeatable and even economical, thanks to modern abrasive advancements.