Ceramic coating for pistons

[dieseldummy]

What does everyone use for coating piston crowns? I used some stuff from Techline coatings (CBC1) and it seems to be ok. I noticed that it has to be applied very thin or it will flake off and need to be redone. Is there anything better that the do-it yourselfer can purchase? Techline has other products, but won't sell it to individuals...

[gmctd]

Dude, real ceramic coating is flashed onto the piston crown at temps above the melting point of sand - it bonds with the raw aluminum at that temp.

Aerosol-driven spray paint won't hack it at combustion temps of 1625deg - 1st time you lite it off, spray paint is smokey history.

[dieseldummy]

Well, the product I used isn't spray paint... It is applied with a small paint gun and then baked on in the oven. I've seen a few people make reference to it in other brands of engine builds so that's why I used it...

[gmctd]

Unless it's baked on at 2000deg, it's just spray paint - takes plasma at 10kdegC to properly coat heat-proofing ceramics, such as zirconium oxide.

Do a search on the 'net for more info.

Those spray-on coatings are for street headers and such, where temps don't get much above 450degF - your EGT's avg 600deg, so most of those are useless for turbo service.

Observing that coating flake off after coming outta the oven oughta be the tip-off, right?

[wthif]

Unless it's baked on at 2000deg, it's just spray paint


but Aluminum melts under 1,225deg F. How long is it at 2,000deg and is it just the top? Just trying to understand how this works, not disagreeing.

[gmctd]

Ceramic coating for aluminum is not baked on, but some coatings cure at those temps - spray 'paint' coatings cure at normal oven temp.

When applied by plasma the ceramic coating is at very high temps, but not very dense, so the mass of the piston reacts such that piston temp can be maintained at lower than melting point, usually less than 500deg.

In the cylinder, of course, the 1625deg flame never touches the piston crown - the expanding gas pushes the crown ahead of the flame front, and the aluminum piston skirt transfers the heat into the cylinder wall, surrounded by the water-jacket.

Timed oil spray into the underside of the crown removes even more heat

In a Diesel engine, excess fuel causing black smoke results in high EGT's, which means the gases that are supposed to keep the crown ahead of the flame front are near combustion temperature, and the fuel, being much denser, holds the heat, which can melt aluminum

Ping in a gasoline engine is result of the flame touching the piston crown - worse-case is melted pistons.

[dieseldummy]

So I guess that the companies who make products I use know nothing then... They claim the stuff I used is good for turbocharged and nitrous applications. Boy, I wish I could get smart and not buy "spray" paint...

[gmctd]

Apologies, dude, wasn't tryin' ta put ya down - the humor just doesn't come across without facial and tonal expression.

But, you can be a PhD\equiv, simply by using the search function on the 'net - that easy access to knowledge was previously only available in colleges, libraries, laboratories, and, sometimes, your next-door neighbor.

This test is simple - if it flakes off in your oven, 'magine what it's gonna do in the blast furnace of your combustion chamber.

Thing of it is, if you try the coating, you won't soon be pulling the heads just to verify that it is in-place and functional, and, oem specs hard anodize - aluminum oxide = ~2600deg - and plasma applied ceramics - zirconium=~1600deg, aluminum= ~2600deg - for combustion chamber and other vht service.

While the piston crown surface never gets to those temperatures, the surface coating must withstand the mild explosion of combustion without burning or flaking off - meaning, the instantaneous temperature increase from cool intake-air cylinder-temps to combustion temps

Suggestion: have your DMax turbo cast-iron exhaust elbow sandblasted inside and out on a low-humidity day (then don't handle it with your bare hands), try the coating on both surfaces, where you can easily pull the elbow and check the situation out - the cast-iron elbow is stable enough to let you see how the coating endures in the wide temperature range of EGT service

Then use Diesel fuel and a paint brush to remove the sooty exhaust residue inside the elbow, so as not to scratch the coating surface - ambient to whatever your upper EGT limit is - 1100, 1200, 1300deg - will define the coating usefulness.

Imo - if ambient-applied spray-on coatings are useful for combustion-chamber service, oem would spec those instead of the much more expensive processes.

What are your thoughts on that?

[dieseldummy]

Well, I would prefer anodized tops like 6.5 pistons... but that wasn't possible. The flaking I experienced was a result of over application. When I was trying to clean the surface off to recoat I found it very hard to remove the coating that didn't flake. After the proper application technique there was no flaking and all was well... I didn't start this one to cause a fight, I was just curious what others have used and with how much sucess. BTW, I do plan on tearing the engine down to check on things.

[gmctd]

You can see a potential problem, right?

Who is gonna pull the engine back down to check the application?

OEM is gonna do the cheapest thing possible to get the vehicle into the collective hands of the customer base - they're still not utilizing those spray-on coatings in that service.

But, yeah - in your case, and it would be a good subject for a thread - preparation, application, results, installation, in-service testing, investigation, results.

In-service testing would require extended high EGT load conditions - not damaging, just high.

IMO, of course.............

[dieseldummy]

http://www.techlinecoatings.com/

http://www.devilscastle.net/

http://www.swaintech.com/

You do the research and see what you think. I already have...

[a5150nut]

Boy! That guy at Devilscastle does some nice work. Wish I had resources and time to do like him. Nice pics and a lot of info there if you look.

[gmctd]

Thanks for the links - I'll check it out:)

I've been wanting something to prevent rust on the turbo and manifold on both trucks.

[john8662]

I've been wanting something to prevent rust on the turbo and manifold on both trucks.

For the purpose of this discussion, this application is for Piston Crowns.

Some research is indeed warranted, to make a more critical review of this particular product and line.

So, let's see it.

J

[gmctd]

True, but while I don't need anything for pistons, I have been wanting something for the turbo and manifolds - properly applied demetcote is no solution.

I would like to see the results of an independent in-service piston crown-coat test, tho.

[john8662]

Back to the original question...

Is Techline Coating's CBC1 coating an appropriate coating, in that it's intended use is Piston protection even in turbocharged applications?

Application technique aside.

J

[dieseldummy]

Ceramic coating for exhaust manifold application is much different from the piston coating. The piston coating is designed to go on thin <.001" and resist combustion processes. Exhaust manifold stuff is designed to be thicker and adapt to different operation characteristics. Will the piston coating or "spray" paint as old JD here says work? I'm sure with the proper cleaning and application it may, but then again, who wants to use "spray" paint...

[gmctd]

Yep - application is very important, as you may know - one fingerprint on the prepared surface, and the preparation steps will need be redone.

The natural oils in your skin - and mine - easily prevent bonding

Same on humid or rainy days - and nites - the beginning of oxidation cannot be seen with the naked eye.

What I meant by needing exhaust coating had nothing to do with coating pistons - I was familiar with some of Techline's and similar coatings, but maybe some improved stuff from NASA R&D is now available, something that won't curl or flake off.

That looks worse than rust.

But, back to the premise - will a spray-on coating for piston-crowns survive turbocharged combustion chamber service?

[arveetek]

What process does the Diesel Depot use? I purchased my 'topped' pistons from them, and they had them ceramic coated for me. Looking back, I wonder about the quality of their products and services....

Casey

[neo]

THis is a great thread as I begin to put together components for my new/next build. I do have a few questions regarding the overall desire to ceramic coat, although I am not tryin in any way to hijack. Is Anodizing not anologous to ceramic coating (Al2O3) through controled "oxidation of the aluminum molocules at the surface of exposure? I have used "hard-coat" anodizing at work for years and find it incredibly durable and hard, so hard that machining back through to the soft alumimun substrate underneath is painfull (and loud!) On the flip-side, as mentioned above is thermal spray (via plasma) which I have also been using, but on other materials that can't be anodized (ferrous.) THe thermal spray is also quite impressive, and very hard/durable as well. Our vendor has even put an Alumina layer on an apple and a styrofoam as a demonstration. IIRC, ther thermal spray does not create near the adhesive bond with the substrate as the anodize process does, thus it seems the anodize would be a better process for as intense of a duty as in a combustion chamber. The reason I ask is for my piston crowns when I build up my engine. Most of the conversation has been "ceramic coating" and I am just trying to understand the best method: Thermal Spray or Anodize (H/C.) and what the general consensus is. Thanks.

[gmctd]

I think it's the economics of plasma vs anodizing, and the utility - a specific area can be plasma-coated without effecting adjacent areas, which would be difficult, even impossible to do with anodizing processes, as the entire part would be immersed in the electrolyte solution.

If I were cutting the crowns to reduce compression, I would prefer hard anodize replacement on the bare aluminum surface, but then, again, I prefer the raised piston-pin solution for that - much easier to do, doesn't effect any of the anodized surfaces, and doesn't reduce the crown thickness, better for turbocharged service.

That's the main difference in 6.2 pistons and 6.5 pistons - the crown is thicker, for the turbo addition.

I like the milled pistons JK offers, tho, because the top cylinder walls are less exposed to the initial flame front, so I would opt for the anodizing to compensate for the reduced crown dimension.

Be interesting to run the two types in identical engines, see how they effected power and ECT's

[CareyWeber]

What would the best thing for a piston that was non coat from the get go?

Carey

[gmctd]

The only non-anodized pistons for internal combustion engines that I'm aware of reside in those .049 nitro-methane fueled glow engines, but the fuel cools those

[dieseldummy]

Last I checked most pistons don't have a hard anodized layer on top... I guess if you're correct then there no difference between 6.2 and 6.5 pistons then huh?

Neo does bring up some intriguing processes. It would be great if hard anodizing was an economical alternative to the "spray" paint process. Maybe Neo can shed some light on where we can get this process done at?

[john8662]

IIRC, the 6.2 and 6.5 pistons are said to differ as GMCTD mentions.

But, this doesn't seem to be verified accuratly.

I'm of the opinion that the 6.5 pistons are no different from the 6.2L pistons in overall crown thickness. My theory is in that the protective coatings on the pistons are different.

This is based on Bohn pistons, which I know were used in most of the production 6.2's, not sure on the 6.5's, but i suspect the same.

I haven't sectioned or measured 6.2 and 6.5 pistons, but would like to verify this measurement.

Somebody on another forum did it, but the measurements were rather crude, so no conclusion was able to be drawn.

I'm not trying to change the subject tho, just to point out what I view is the difference, coatings...

J

[CareyWeber]

The only non-anodized pistons for internal combustion engines that I'm aware of reside in those .049 nitro-methane fueled glow engines, but the fuel cools those

GMCTD,

Sorry I meant to add that it's a diesel, but not a 6.2/6.5 or even other GM diesel its's an old Nissan SD33 and they are hard on pistons.

Carey

[gmctd]

Dunno, Carey - would depend on whether it's cooking the crowns, scuffing the skirts, or just cracking out

[CareyWeber]

Dunno, Carey - would depend on whether it's cooking the crowns, scuffing the skirts, or just cracking out

GMCTD,

Cracking mostly.

Carey

[gmctd]

According to one piston expert, anodizing the crown prevents thermal-cracking, but has little to do with hi-temp protection, as the barrier is too thin.

IIRC, those SD-33's were designed for ~ 60-70hp, and I can't imagine Nissan over-designing the engine, so maybe that is normal for those pistons in their oem form.

Possibly there were upgrades in later years, but you will need to determine if the initial failure is thermal or mechanical to determine the solution - may just require replacement, as necessary, if the pistons were under-rated.

[neo]

Sorry for the delay: work, kids, wife and parents, We all know the drill...
We use one specific vendor (Cincinnati Thermal Spray) for plasma spray ceramic coating. They are very good. They can do a series of different plasma sprays including Alumina, Hastelloy, Zirconium and several others. There web site is: http://www.cts-inc.net The process requires different "mating" layers, what they call MCrAly, I believe, which is a metal-chromium -alloy layer used to match the CTE of the final ceramic coating to the substrate. I will call the prod supervisor and see if I can get an idea on what it woudl cost to do a set of eight crowns. They have done quite a bit of work for me and it is neat stuff. I have never seen it flake, it is very hard and does not scratch that I have seen. Gotta plug any threads though so material does nto get in there. Let me know if I can help anymore and I will keep following the thread.

[dieseldummy]

Their site has alot of info on it. Thanks for the link! :D If it would be cost effective that sure looks like it would be a good way to protect our little old piston crowns.

[CareyWeber]

According to one piston expert, anodizing the crown prevents thermal-cracking, but has little to do with hi-temp protection, as the barrier is too thin.

IIRC, those SD-33's were designed for ~ 60-70hp, and I can't imagine Nissan over-designing the engine, so maybe that is normal for those pistons in their oem form.

Possibly there were upgrades in later years, but you will need to determine if the initial failure is thermal or mechanical to determine the solution - may just require replacement, as necessary, if the pistons were under-rated.

GMCTD,

There were many upgrades to the SD33's when they turbo'd them they got a pistion oil cooling jets to spray the bottom of the pistons and they also got a new piston with a steel carrier for the top ring and that ring is a keystone ring there are a total of 5 ring s per piston.

If I were to guess why they crack there are two reasons:

1st they are 28 yrs old and likely have never had the injector serviced.

2nd with the tubo the EGT's get to high (engine and injection system in good condition).

All the pistons are completely uncoated though.

How important are Keystone rings in a Diesel?

Carey

[gmctd]

Prevents excessive blowby at high compression ratios and high combustion pressures while reducing excessive ring tension.

IIRC, top fuelers were using them for nitro, keeps the stuff outta the crankcase.

[CareyWeber]

Prevents excessive blowby at high compression ratios and high combustion pressures while reducing excessive ring tension.

IIRC, top fuelers were using them for nitro, keeps the stuff outta the crankcase.

There are SD33 pistons with the steel carrier, but with a non-keystone ring.

So would you coat these pistons if you were doing a rebuild?

Carey

[gmctd]

Which piston gets the keystone - turbo or non-?

You still need to determine what initiates the failure - excess heat from the crown or thrust stress at the pin bore, or?

Coating will help the first type, but not the second, which would require struts or more aluminum, oem processes.

Or, perhaps, chamfering the ends of the pin-bores, radiused keeper-ring grooves, same or less undercutting in the ring-grooves, etc.

If the skirts\cylinder walls are always scuffed at failure, maybe increased bore clearance

Determining the root cause will define the cure

[CareyWeber]

Which piston gets the keystone - turbo or non-?

You still need to determine what initiates the failure - excess heat from the crown or thrust stress at the pin bore, or?

Coating will help the first type, but not the second, which would require struts or more aluminum, oem processes.

Or, perhaps, chamfering the ends of the pin-bores, radiused keeper-ring grooves, same or less undercutting in the ring-grooves, etc.

If the skirts\cylinder walls are always scuffed at failure, maybe increased bore clearance

Determining the root cause will define the cure

The Turbo pistons are keystone.

Here is a link that show a tipical piston failure in a SD33T the NA SD33's aren't as hard on pistons.
http://www.binderbulletin.org/forums/showpost.php?p=338073&postcount=76

Carey

[gmctd]

Don't know how much clean-up he did for the shoot, but even hard-anodizing won't help, much - that appears to be long term high-egt, maybe aggravated by several bad injectors.

IMO, what would help is an EGT gage and a Boost gage, and an oil temperature gage, and monitoring the engine coolant gage - learn to use them and correlate the readings.

The PCM for that engine is between the driver's ears, right?

[CareyWeber]

Don't know how much clean-up he did for the shoot, but even hard-anodizing won't help, much - that appears to be long term high-egt, maybe aggravated by several bad injectors.

IMO, what would help is an EGT gage and a Boost gage, and an oil temperature gage, and monitoring the engine coolant gage - learn to use them and correlate the readings.

The PCM for that engine is between the driver's ears, right?

Yes right between the ears.

We had one guy that cracked a set of new pistons right after a rebuild.

I think the SD33T needs an intercooler.

I was thinking that the coatinf would be helpful if everything else is in good working order.

Carey

[gmctd]

I think so, too - but anodizing and 'cooler won't help unless the owner learns some hard facts about turbo-Diesels, and toes the limits.:)

[dieseldummy]

Well due to a blown head gasket I finally got a good reason to pull the heads and check up on this "spray paint" ceramic coating. The coating survived and didn't "flake" off during combustion and leave the pistons to melt. There are a couple of pistons that have been hot due to a sticky injector/used motor oil fuel situation and the ceramic discolored slightly, but didn't fail.

I feel confident that the CBC1 coating I used is sufficient for high performance turbocharged use. I've ran EGT's upto 1450 before with the marine injection pump/injectors and over 30lbs of boost and it held up.

For anyone who wants ceramic coating on their pistons I believe that this is the way to go. IIRC, the bottle of coating was under $100 and will do several sets of pistons. All that is required is a detail paint gun, an oven(preferably not the one in your kitchen), and a little bit of time. The key is prep work and not over applying the product. I learned that if it is applied to thick it will bubble and flake off during baking.

Hope this helps someone down the road when they need to build a motor.;)