Cylinder coating

Hey, everyone,

I've heard recently that the cylinder walls of automotive engines have microscopic scratches purposely engraved in them for retaining oil and, thus, improving lubrication. First of all, I'd like to know - is this is true? If it is, then it seems like coating the cylinders with a ceramic (or some other) coating in an attempt reduce friction or reduce heat loss would fill up these scratches and defeat their purpose. Yet, companies do offer ceramic coatings for car engine parts, including, if I am not mistaken, cylinder walls. Any light on the subject would be greatly appreciated!:)

Yes, you're right about both. The scratches ("honing pattern" or "hone pattern") are put there intentionally, and they are supposed to retain oil on the cylinder wall. Coating the cylinder wall can potentially cover up the honing pattern and result in reduced lubrication.

Reduced lubrication is not necessarily bad:

Two of the largest contributors to friction within the running engine are the piston rings to liner interface and the piston skirt to liner interface. These interfaces can account for nearly half of the friction losses within an engine. The interesting thing (to me) is that special coatings are very unlikely to have a significant direct impact on this friction.

The reason? Metal-to-metal contact is rare at these interfaces. Under most operating conditions, the oil on the cylinder wall separates the rings and the skirt from the liner. A ZERO-friction coating on the surface of the cylinder wall, in a typical engine, would probably result in about a 10% reduction in friction at the aforementioned interfaces.

What accounts for the rest of the friction? The lubricating oil itself does. Hydrodynamic losses represent the vast majority of friction power at these interfaces. The hydrodynamic losses can be most easily reduced by reducing the amount of oil on the cylinder wall, or by reducing the viscosity of the oil. Unfortunately, both of these methods are likely to result in increased metal-to-metal contact, and thus wear. Also, increased metal-to-metal contact can INCREASE the friction you set about to reduce.

Possible solutions:
* Apply lubricating oil liberally where you most need it, such as at the upper and lower ring reversal regions, and sparingly where you don't. One way to accomplish this is through selectively honing regions of the cylinder liner (top and bottom reversal regions), while polishing the rest of the liner smooth. At least one company uses lasers to achieve this result ( http://www.gehring-group.com/ look under honing | laser honing).
* Use a wear-resistant surface treatment on the cylinder liner, and either supply less oil or use a lower viscosity oil. Easier said than done.
* A combination of the above
* Design an engine that runs without lubrication (there are some people who claim to have ceramic engines that do this; I'm convinced that the vast majority are lying).

Thanks for such a detailed reply! This is very helpful indeed.

In many racing engines Apticote 2000 are used to coat liners and blocks.
http://www.poetonaptec.co.uk/

So do you think that ceramic coating is beneficial? I.e., do a reduction in wear and improved durability compensate for poorer lubrication? How much does the answer depend on the actual material used in the coating?
If you are interested, the reason I am asking is because I want to find out if XADO really works. It's a new oil additive developed to do just that - create a thin ceramic coating on the moving parts of the engine:
http://www.xado.com/text/uk/faq/xado.htm

do a reduction in wear and improved durability compensate for poorer lubrication?
They can. It all depends on the relative magnitudes of the changes. Obviously, if you double wear by reducing lubrication, then reduce wear by a third through the use of a coating, you're worse off than you were initially.

If you are interested, the reason I am asking is because I want to find out if XADO really works. It's a new oil additive developed to do just that - create a thin ceramic coating on the moving parts of the engine
My guess is no, but I don't have any test results to back that up. The writing style used on the website (uses big words but doesn't say much), and the suggested applications of the product (perfect for anything rubbing anywhere), suggest to me that the product is "snake oil." In general, I've found that if a guy is trying to sell you something, and all he does is recite a bunch of positive-sounding yet nearly meaningless sentences (while smiling vigorously), he is looking for a mark. Remember, if it sounds too good to be true...

One function for the coatings in racing engines (apticote 2000 as one example) is to retain the oil in the cylinders, especially this is very important in high speed engines such as F1 engines.
But it's also used in "standard" racing engines such as the ones in BTCC cars. As one example I can mentioned the TWR/Volvo engine, theese engines have some of the highest bmep for NA engines. On the other hand one of theese engines cost around $80,000.

And about XADO, it seems like just another "snake oil".

Sorry to bring back on old thread, but I recently just came across this Xado stuff myself in another forum and wanted to share what I found, and ask for more opinions, given any new information.

http://www.3si.org/forum/showthread.php?t=214253&page=8&pp=10

This is the thread I heard about it in, but it is 24 pages, so it takes awhile to get through.

I summarized it and wrote my main concerns here:

http://www.automotiveforums.com/vbulletin/showthread.php?t=361874

Just wondering if any of you techincal gurus, had any new opinions being that they have crossed the language barrier that was there 2 years ago (which probably accounted for the lack of actual factual information on their website)

Thanks for your time.