We’ve brought you articles in the past (mostly with Lake Speed, Jr. too, come to think of it) on the science behind honing, the science behind measuring your pre- and post-hone surface finishes, as well as the performance theories behind honing strategy. It’s safe to say, not only is the surface finish of your cylinder crucially important, but the right hone has net you both power and longevity.
This testing isn’t so much about proving a theory or trying something different, but rather to see what is happening with a surface finish of your cylinder between being freshly back from the machine shop, after assembly, and then finally what the surface finish looks like after a proper engine break-in procedure. Before we dive into that, let’s make sure everyone is on the same page.
First is the terms and measurements well be using. To measure the surface finish, we’ll use a profilometer. This tool uses a drag stylus to measure the roughness of the cylinder wall down to the millionth (.000001) of an inch, or 1 microinch (µin), if you prefer. Those units are used to measure three main features. The height of the peaks of the surface are known as “Rpk” (or peak roughness). The core roughness measurement is known as “Rk”, and the depth of the valleys is known as “Rvk.” (If you want to get way deeper into those measurements, you can check out some of our other articles.)
The next thing to understand is plateau honing. This is a method of honing that uses a coarse hone to create deep valleys (a high Rvk number), and is then followed with a very fine — much finer than you would use alone — hone to flatten out the peaks (get a low Rpk number), without removing the deep valleys, creating a “plateau.” The idea behind this is to provide a less abrasive surface for the piston ring to seal against, while providing plenty of space for the oil to live in on the cylinder wall.
Before rotating the short-block by hand, the cylinders were perfectly clean. So there is some significant wearing-in happening before the engine ever gets on the dyno.
With that out of the way, it’s time for the testing. For the start of the test, the cylinder measured 10µin Rpk, 39µin Rk, and 69µin Rvk. Out of the hone, that is a very solid set of numbers that almost anyone building a high-performance engine would be thrilled with. After getting the rotating assembly installed, Lake spun it over by hand a number of times to simulate what you would typically see during the entire assembly process.
Before measuring the surface finish again, a quick wipe of the cylinder showed new material deposits, indicating that something had worn against something else in the cylinder. The numbers show that the peaks started to round off by simply rotating the engine by hand a few revolutions. With that data recorded, the engine was assembled and thrown onto Pro Motor Engine’s dyno, and run through a proper engine break-in cycle.
The results are both as expected and surprising as well. The Rpk numbers — or should I say number — was down into the single digits, the core roughness was almost halved (since it’s an averaged measurement, reduction in Rpk will also reduce Rk), and a majority of the valley depth was retained. Making the finish exactly what the piston ring wants when operating at speed in an engine.
To see the exact final numbers, or if you just really want to see all the data from the profilometer and the images from the microscope, you’re going to have to watch the Total Seal video above. It’s well worth the eight-and-a-half minutes of your day if you’ve ever even thought about your cylinder wall’s surface finish before and after engine break-in.
Pro Motor Engines’ dyno ran the engine through a complete break-in cycle. The engine was then taken back off the dyno, disassembled and the cylinder wall surfaces were remeasured.
