For a long time, people have poked fun at the DIY honing products. Some people swear by them to get their desired crosshatch angle in a home rebuild, and others outright condemn them as doing nothing of any real effect. At the end of the day here at EngineLabs, we are all about the data. Since we are close to Total Seal, and we know they have stacks of profilometers sitting around, we decided to put the ol’ dingle ball hone to the test.
“The idea of plateau honing is that you go through with a coarse abrasive, and ‘dig the valley’ before using a fine grit to level the peaks off,” explains Keith Jones, Total Seal’s Director of Technical Sales. As we’ve covered in the past, honing science has greatly advanced in the past decades. But, one of the key takeaways is that while advancements are made, that doesn’t invalidate the older methods.
“Ball hones can’t really change bore geometry, because they aren’t exerting enough, or the right kind of pressure on the cylinder wall,” says Jones. “What they can do is re-establish the finish of the cylinder surface. You could sit with this [320-grit ball hone] in the cylinder for two days and not even remove two-thousandths of an inch of material.”
Setting Up The Test
For this test, we decided to use one of the Mitutoyo SJ-210 profilometers that Total Seal sells, that they’ve specifically set up for checking the surface finish of an engine cylinder. As the guinea pig for the project, we threw Project Retro 5.0’s bare block onto a cradle and into the back of the truck, and headed down to Total Seal. The block was in the exact condition in which we got it — ostensibly a lower-mileage piece, and completely untouched since the initial teardown.
There were four measurements we were interested in on the block. The first was the bottom area of the cylinder that had been machined from the factory, but never had a piston ring wear against it. The second was the swept area of the cylinder that had been worn, to assess the condition of the bores, as they sat. The third measurement would be after we ran the ball hone in the cylinders, and the final measurement would be after giving the block a proper hone.
After a quick wipe down of the cylinder, the stylus was placed on the “unrun” portion of the machined cylinder to see what the baseline numbers were when the engine left the assembly line. The SurfTest showed an average roughness (Ra) of 24.50 microinches (µin), core roughness (Rk) of 77.23 µin, reduced peak height (Rpk) of 15.68 µin, and a reduced valley depth (Rvk) of 49.00 µin. “Considering this was 30 years ago, those are pretty decent numbers from the factory,” Jones says.
The factory cylinder finish numbers are a nice data point to have, but the real numbers we want are what the cylinder finish is, currently, in the swept area. After two traces to be sure the numbers were right, Jones’ face told the story before we even saw the numbers. “This cylinder is wiped out,” says Jones. The numbers concurred, showing an Ra of only 5.47 µin, an Rk of 9.60 µin, an Rpk of only 1.93 µin, and an Rvk of 31.70µin.
Hitting It With The Ball Hone
“I don’t think a ball hone is going to do much there, unfortunately. These kinds of hones, ball hones especially, aren’t there to add depth back into the cylinder walls, but rather to smooth out the peaks,” Jones says. However, in the name of science, we decided to at least give it a whirl before heading over to the machine shop to drop the block off.
For the test, your author purchased a brand-new Brush Research Mfg. Flex-Hone (P/N: GB41832) from Summit Racing, much to Jones’ delight, saying, “It’s not every day that you get to play with a brand new hone!” Per UEM’s recommendation, we chose a 320-grit silicon carbide version in 4.125-inch diameter for the engine’s 4.00-inch bore.
Per BRM’s instruction sheet, the recommended brush RPM range is 350-600 rpm, with an acceptable stroke rate of 100-250 inches per minute. However, those numbers are just guidelines, and instead of measuring exact RPM and stroke rate, we simply aimed for creating a solid 45-degree crosshatch angle (measured at 22.5 degrees on Total Seal’s angle finder card).
With that in mind, your author chucked the hone into a cordless drill motor and handed it over to Jones to do the dirty work, to which he graciously obliged. Since the goal of this test was to replicate what the average enthusiast would be doing in his garage, we used good old WD-40 to lubricate the hone and the cylinder walls, and Jones got to it.
After a dozen strokes, we pulled the hone from the bore, cleaned out the cylinders and reapplied the profilometer stylus, and let it do its thing. An odd look from Jones suggested he wasn’t seeing what he expected, and he retested. A “Hmmm…” was followed by re-lubing and reinserting the hone for another 10 or so strokes.
After repeating the cleaning and sampling process, Jones declared that the trip to the machine shop might not be needed. “I certainly didn’t expect to see the cylinder come back like this. We have pretty solid numbers all around, including adding some Rvk, which I wasn’t expecting at all,” says Jones of the new numbers.
The Mitutoyo profilometer’s readings showed new cylinder measurements of 15.91 µin Ra, 42.68 µin Rk, 13.47 µin Rpk, and 49.26 µin Rvk. “These aren’t perfect numbers, but you’re about 90-percent of the way there,” says Jones. “For what you are doing with this project, the type of rings you’re using, and the angle you are taking, these are perfectly acceptable numbers. I’m genuinely surprised by the ball hone’s performance here, and it’s not often I’m surprised.”
What Is Deglazing?
During the course of this test, the term “deglazing” popped up several times. Brush Research defines glazing as the smoothing or polishing of the cylinder wall over time due to the friction of the piston rings. That polishing doesn’t allow oil to adhere to the cylinder wall. This not only increases friction, it can prevent proper seating of new piston rings to the cylinder. By running the hone in the cylinder, the super-smooth finish is “roughed up” much like preparing a surface for painting. However, deglazing won’t typically add any valley depth to hold onto the oil, so if the cylinder is too worn, deglazing alone won’t provide a proper surface finish for new rings.
Ball Hone Conclusions
What started out as almost a joke, ended up leading to some serious data. While the idea of using a ball hone — and only a single grit of ball hone at that — might seem ludicrous to some, there’s no denying the data that came out of the test. If this was a high-end, max-effort engine, we would absolutely be heading down to the machine shop and asking them to hit it with diamond and CBN hones, and would worry about every single spec being brought into the optimum range.
However, this is an “average enthusiast” build, and this is one of the few instances where “good enough” actually is “good enough” for us. If the ball hone gets us 90-percent of the way there, for only the cost of the hone, it seems like a reasonable course of action. Since we will be able to measure blow-by on the dyno, we’ll be able to tell definitively whether it was the right course of action. Until then, stay tuned for more Retro 5.0 content, done in the name of science.