Cross-hatch - what it is and what's it's supposed to do:
The technique was developed as a means to provide pistons with needed lubricant in order to prevent seizure and improve ring face wear. It is typically done during the cylinder boring process, when finer stone grits are used to size the bore while at the same time achieving the desired surface roughness to hold oil on the surface.
On the face of things, cross hatch accomplishes that goal, but that process results in some serious compromises in terms of overall ring sealing properties and actually does a poor job of lubricating the ring faces, thereby allowing ring face wear which increases as combustion gas pressures rise.
Understanding these limitations the industry started to use a variety of approaches to flatten the surface, which most refer to plateau honing. While this improves the overall roughness, it does little to remove the "channels and ridges" that are a result.
Take a close look at the image below. Notice the the surface is actually a series of rectangular channels" and raised "ridges. Think of those ridges as railroad tracks and the "valleys" as the area between those raised tracks. It's true that oil is trapped in the valleys and some of that is picked up by the ring faces with each stroke which only provide limited lubrication to prevent ring face contact. There are two problems with this approach:
As the image illustrates, the actual contact area of the ring face is reduced, somewhere between 30% to 50%. Compare the ring face to a typical shell-type engine bearings. Their success depends on having enough lubricated bearing area under load to prevent the surfaces from making contact with the crank or rod ends.
In the case of rings, the area of the ring face is intended to prevent the ring face from making contact with the bore. Would you use engine bearings that are only half as wide? Of course not, a spun bearing will surely result. So if we reduce the rings "bearing area" by 30% to 50%, what's to prevent the ring face from touching the raised area of the cross hatch and ring wear?
Any engine is simply an air compressor. It pumps air and the better the parts work, the more air it makes. It's that simple.
We all know how pistons and rings work, the pistons go up and down, driving the crankshaft and the rings create a gas seal to keep the gasses in the combustion chamber where they belong. And for the most part, they work well, but could they work better?
Our problem with cross-hatch:
1) Cross hatch does indeed trap oil, but since it's below the surface of the ring contact, it then travels past the rings into the combustion gasses, not a good thing in race engines. Because of this, the best oil rings cannot prevent it.
2) Since the ring's face sealing area is reduced by 30% to 50%, what's to stop gasses from being pushed through the "valleys" resulting in gas leakage?
Our solution - eliminate the cross-hatch and coat the bore with MicroBlue®
Several years ago, our friends at Millennium Technologies came up with a new cylinder plating finish that virtually eliminates all the problems detailed above.
MicroBlue® improves the way lubricants "wet" the surface (by reducing the surface tension of the oil film). Because of this action, lubricants are attracted to the coating and the result is a uniform oil film which prevents piston and ring contact and most importantly, allows the rings to "water-ski" on the bore surface, eliminating wear. In addition, the dampening effects due to the increase in land oil volume eliminates ring flutter.
This accomplishes three things: One, since there's no ring contact, all wear is eliminated. Second, since an oil film is more effective at transmitting heat, piston temps (and EGT's) are reduced dramatically. Third and and most importantly, it now takes some real work to seize a piston.
For more information about your application, contact Millennium Technologies at 888-779-6885. Information on their plating services can be found here: https://www.millennium-tech.net/
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