Aluminium oxide ceramic coating of Piston crown

[tommurphy73]

There has been a lot of talk about ceramic coating the crowns of pistons to improve the insulating properties of the piston and keep the heat where it can do the most use inside the cylinder. The most commonly used ceramic as far as I am aware is aluminium oxide which is deposited on the suface and using heat is bonded to the surface. Recently I have seen some debate as to wheater these coatings are any good.

Other coatings are also available for the piston skirt which are widely accepted as being benificial by reducing friction but it is very difficult to get hard facts and numbers to substanciate the claims.

What are you guys thoughts on this?

Regards
Tom

[rookie]

Originally Posted by tommurphy73

There has been a lot of talk about ceramic coating the crowns of pistons to improve the insulating properties of the piston and keep the heat where it can do the most use inside the cylinder. The most commonly used ceramic as far as I am aware is aluminium oxide which is deposited on the suface and using heat is bonded to the surface. Recently I have seen some debate as to wheater these coatings are any good.

Other coatings are also available for the piston skirt which are widely accepted as being benificial by reducing friction but it is very difficult to get hard facts and numbers to substanciate the claims.

What are you guys thoughts on this?

Regards
Tom

The coating I use on piston crowns, combustion chambers and valves is Powerkote CBC1 or 2 depending on application and the same brand dry film lube for skirts, the aluminum oxide is the blasting media used to etch the part so that it absorbs the coating.
Then you bake it in for an hour at 300 degrees.
I have run a 350 small block Chevy on the dyno for 21 pulls with 12.5 compression.
More than half the pulls was on nitrous and the engine on the bottle made between 715 and 820 horse, the biggest shot we fed it was 300 horse plate.
The plugs were ghost white and speckled indicating lean, as a matter of fact we pushed the engine so lean that at tear down we found the top ring on #3 cylinder was broke, the ring gaps were set tight at only .024, but the pistons were perfect, as a matter of fact the underside of the piston had no color, this indicated the crown stayed cool, usually they will have a brown color to black if to hot or a big hole if way to hot.
(I put David Vizards name and the word coatings and found this at the top of 155 results.
The May 2003 issue of SPEEDWAY ILLUSTRATED has an article on "Port Volume" written by David Vizard. On pages 79 and 84 a photo of a combustion chamber appears. On page 84 it notes that it is a Coated unit. Coatings are becoming common enough that no special mention is made of them. This is a further indication as to the trend towards more and internal engine coating taking place. Keep your eye open for details such as this as it helps convince the few unbelievers remaining, of the error of their ways.)

My understanding is that coatings work so well they are becoming the standard practice to be competitive.

[DavidVizard-GFN]

Tom-
We have to watch out for the characteristics of the coating used on piston crowns. Just insulating can actually lead to total destruction of the piston. The key is that the coatings need to not hold heat and must be able to temperature cycle very quickly so as to avoid becoming a hot spot in their own right. Jet engine coatings so often used in the early days (25 years ago) of coating exploration are the worst deal here. What we need is something that is impervious to heat. It neither accepts it or rejects it. Can’t be done at present but modern coatings are much better at emulating this.


As Rookie implies coatings are a god-send when it comes to high boost, compression or nitrous. Since I have been using coatings on piston crowns I have not lost a single piston in a nitrous engine. Again a Rookie pointed out the tell tale sign of low heat transfer is the lack of discoloration on the underside of the piston.

[DavidHarsay]

Additionally, Techline has some information on their website. Just consider the the source or motives when reading it, it's good information none-the less.

Coating Pistons

One note about DIYS coatings though... it needs to be applied properly, to a proper surface, otherwise the results may not be too good.

[tommurphy73]

Originally Posted by rookie

My understanding is that coatings work so well they are becoming the standard practice to be competitive.

Dont get me wrong, I am a huge fan of coatings. I have in fact used the techline coatings CBC2 and cermalube to good effect in the past. However I was talking to a friend mine recently about ceramic coatings as he worked on them in the electronics industry. He said that Aluminium oxide is the most common ceramic with excellent insulating properties (CBC2 is mostly aluminium power). Based on his experience he thinks that a more effective way to put a ceramic coating on a piston is to use an anodizing process. By using different voltages it is possible to control the surface finish of the ceramic and control the thickness of the anodized layer. The hardness of the layer could be further enhanced by heat treating the piston after anodizing. It could even be made a nice color. Since it is not sprayed or otherwise applied to the piston there is also no risk of it chipping off.

Just some thoughts

Best Regards
Tom Murphy

[Regal502]

Just FYI....... Dart (the manufacture of cylinder heads and blocks) also offers coating service. I had my combustion chambers, valve faces, and exhaust ports all done-- and their prices are reasonable too! Contact Omar at Dart.

~Tom

[hotrod]

I have recently seen reference to use of hard anodizing on piston crowns.

Hard anodizing is the same "coating" used on electical component heat sinks. It uses a chemical process to convert a bit of the aluminum surface to a thin layer of chemically bonded aluminum oxide (which is a ceramic).

Wiseco advertizes anodized pistons for Chrysler outboard motors.
http://www.wiseco.com/PDFs/Catalogs/...yslerForce.pdf

The Chrysler (4.7L) V8 also is supposed to use hard anodizing on the top ring land to protect it as they made it very narrow for emissions purposes.

Mopar Action magazine. Volume 10 Number 3 (April 1999) had an article that included the following excerpt on piston design.

Pistons are cast aluminum, have moly coated skirts for break-in scuff resistance, and weigh 366 grams. They are fitted at 0.0008-0.0020" skirt clearance - rather snug but nothing unusual for a street engine. The usual 3-groove ring pack is used (.062/.062/.120") but in addition to the common plasma-moly-filled top rings, the second ring is chrome. Oil rings are chrome as well, with a stainless expander. Bucking the current trend, the oil ring tension is rather high (12 lbs) allowing good oil control even in high-mileage engines. In fact, the spec for the 95th percentile customer is 150,000 mile useful life.

In the never ending quest to reduce emissions, the distance from the top ring groove to the top of the piston has been reduced to only 1/8th of an inch, making these areas susceptible to excess wear and heat. To combat this, the top ring land, and the area from the land to the head, are hard anodized.

Here is another web page that mentions the concept.
Evolution of Piston Design

I think hard anodizing the whole piston crown might be a useful idea if the coating bonds tight enough it does not de-laminate. It certainly has much higher hardness and temperature limits than the underlying aluminum.

Larry

[DavidHarsay]

How is the Phosphate coating applied to Mahle pistons? And what are the benefits?