Honing an engine block with a Pro Stock legend Greg Anderson
In the past we have discussed that different piston rings and different applications of use all have slightly different honing techniques. While most builds will likely be pretty forgiving with a hone with numbers a little more one way 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 are exact.
Modern piston rings are a different animal from rings of a decade or two ago. On top of that, our understanding of what is actually happening on and within the cylinder walls is more advanced than ever before. So it stands to reason that today’s processes and methods are different – and significantly better – than they were just a few decades ago. Anderson of KB Racing, along with Lake Speed, Jr. of Total Seal, walk through the process of perfecting a block for a modern ring set.
Make a round hole
“The first key is to spin the cylinder,” says Anderson. There are two key elements to doing this: a quality lapping machine, like the Rottler H85AX Anderson uses, and the use of a torque plate on the block. “If you were to hone that block without a torque plate and then bolt your head on, the bore would be a completely different shape,” Anderson says.
The torque plate is an analog of a cylinder head, 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 put all the stresses in the block that will be present when the engine is assembled, then ensuring you create a round, straight hole.
The first step in preparing for a modern cylinder finish is to use a modern abrasive. “We use a 170 to 200 grit diamond cutting stone,” Anderson explains. We’re looking for a certain groove depth, basically the Rvk. You might recognize the term “Rvk” in some of our other break-in articles; it is the measurement of the “valley depth” of the cylinder finish, as measured by a profilometer, in microinches.
“This valley will trap the oil behind (or below) the surface on which the ring sits,” says Anderson. “As we’ve found over time, we need that groove to be slightly deep, because without oil you have problems. Years ago everyone liked to sharpen the very very fine cylinder. The thought was that reducing friction was everything. The problem is that with that nice finish, you ran out of oil on the surface and then went back to a high friction scenario.
The modern board
The idea of sharpening the plateau is pretty self-explanatory – once you’ve created the deep valley, you have equally high peaks. These picks would be quite abrasive on the rings. The idea is therefore to cut down the peaks without touching the valleys. “We’re going to hit a plateau with a 600-grit CBN sharpening,” says Anderson. “CBN” or Cubic Boron Nitride is a modern abrasive that is both extremely hard and extremely durable. It is able to cut cleanly and quickly, providing minimal heat buildup with an excellent finish.
By removing the tops of the peaks, but retaining the valleys, you create a beautiful, low friction surface that also has the ability to hold oil effectively. “The surface the ring rolls 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 get a final finish in fewer strokes, which has both quality and productivity benefits.
“Now we go to less than a tenth of a thousandth of the finished cut with the diamond, and then you go to your 600-grit finishing CBN, and you really don’t remove any additional material,” Anderson says of the process. . “Back then, people would come within a thousandth of the target and start taking two or three tenths off with this stone, then two or three tenths off with this stone – all the while taking their valley away. If you gradually finish drilling, you completely remove your valley.
Speed agrees, saying, “The old platter method was to hone with 320 grit at the waist, then 400 grit to finish. Your cylinder walls really couldn’t hold enough oil. But since the old rings were Moly based, they were porous and held the oil on their own, so they allowed you to do that. The modern materials used in today’s advanced bushings no longer mask the shortcomings of the old honing methodology.
“Rings today have a very hard coating and you’re really not going to wear them too much. It’s a very, very flat surface, and nowhere to hold the oil in the ring, so [the oil] must be held back by the bloc,” Anderson summarizes. At one time the battle was between piston ring makers and piston makers to see who could make a more accurate product. Now the challenge is to create the perfect cylinder surface for these advanced piston rings every time. Thanks to modern materials and methodology, it is not only feasible, but reproducible and even economical, thanks to modern abrasive advances.