Piston coating

Post Reply
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Piston coating

Post by kb1gtt »

Does anyone know if Cerakote-ing pistons is worth it?

Welcome to the friendlier side of internet crazy :)
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

I am not familiar with "Cerakote" but I expect it is similar to some other ceramic coatings. I will double check when I am not at work and can watch the video.

However there are some pretty decent benefits to piston coatings but which to use depends a lot on what your trying to get out of it.

Thermal barriers can help a lot with piston crown temperatures and thus crown longevity in boosted engines but the downside can be greater heat rejection into the cylinder head, sometimes having both head an pistons done in thermal barriers can be a recipe for a detonation disaster.

The moly coatings and anti wear coatings are pretty great at reducing piston slap and skirt wear on slipper pistons, there is a company that does a full graphite skirt coating that allows you to run the skirts at zero clearance or pad up a worn piston for restoration purposes, I have heard that one is pretty great.

Another cheap and very effective option is to hard anodize the pistons, gives a couple of benefits, hardens the surface to prevent wear and prevents some fatigue as its always at the surface cracks start, works as a thermal barrier as the alu oxide on the surface is a bad conductor of heat and very thermally stable and also has a porous structure that traps oil. A win on most accounts just not as good at any one thing than the more specific coatings.

Overall yeah, piston treatments can be well worth it just pick your treatment to suit your need.
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Re: Piston coating

Post by kb1gtt »

I recall Teflon coating as well. Theory being that it's a great dry lubricant, so it helps keep things from sticking to the top of the piston and prevents these ridges from poking thought the boundary layer. The results are colder crown temperature.
Welcome to the friendlier side of internet crazy :)
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

Interesting, not looked into teflon for pistons too much. Did consider getting a bike frame coated though when I was working with a chinese factory that did it. Love to see mud stick to that. :lol:

Colder crown temps is a tricky one, as the heat that doesn't go into the crown has to go somewhere and the answer is often into the head, exhaust ports and cooling system instead of into the oil system via the pistons. Personally a fan of oil squirts and lowering oil temps to reduce piston temps I have seen data that can see this bring down crown temps by up to 100 degrees C.
To help save marginal durability pistons it's a good shout but for lower temps I prefer forced cooling where possible.
Just my $0.02

FYI - looks to be cerakote V-136 they are using, normally a supplier of gun coatings.
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
puff
contributor
contributor
Posts: 2961
Joined: Mon Nov 11, 2013 11:28 am
Location: Moskau

Re: Piston coating

Post by puff »

IMHO when you heat teflon to some temperature, when it burns, it generates some toxic gases that are much more dangerous than novichok
https://en.wikipedia.org/wiki/Polytetrafluoroethylene
see safety chapter
so, coating pistons with teflon is probably not the best idea.
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Re: Piston coating

Post by kb1gtt »

Correct, Cerakote has a reputation as a hard and very rugged gun coating. I'm not sure why folks don't seem to be coat the head. I've only seen the pistons coated. It seems odd to me, if they want it colder by taking the heat away in the exhaust, why not coat everything? As well that coating on the sides is likely garbage. I see that as created a thermal resistance to your heat sink. Perhaps they think that it helps keep oil on the side of the piston and increases lubrication. It seems odd to me coating the side of the piston. The goal is to keep the boundary layer, not really to keep things hot or cold. However the colder the metal, the thicker the boundary layer.

If you have heated PTFE hot enough to out-gas in your engine, you have other problems. It melts at 327 °C at 1bar, and goes gaseous at even higher temperatures. As well, over heating your home cooking pan is more of a concern than the small amounts you might potentially get our your exhaust.
Welcome to the friendlier side of internet crazy :)
ZHoob2004
contributor
contributor
Posts: 153
Joined: Sun Apr 03, 2016 7:11 pm
Location: Tucson, AZ

Re: Piston coating

Post by ZHoob2004 »

If I recall, this guy has both coated pistons and cylinder head parts, and he's making some very impressive numbers for a rather antiquated engine design.

http://forums.hybridz.org/topic/123487-compare-your-dyno-sheets-here/?page=2&tab=comments#comment-1181965
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

The reason for not coating the head is the same as the reason for not using iron heads, you do actually need a cold chamber if you want to make power because if the chamber is cooler then you can generate higher pressures before abnormal combustion occurs.

The piston has to be both very light and resist a lot of heat so the coatings can help keep a thin crown piston intact but the result of not sending the heat out via the piston is more is held in the chamber to exit in other ways.

If you coat the piston and the head then there is even less heat sink area to cool the chamber down as so the residual gas stays red hot from the last burn. Which is obviously bad when you introduce new air fuel mixture and increases the risk of detonation.
By making the metal temperatures colder your trapping the heat and making the gas temperatures higher which can be a bad thing.

Take a look at how compression ratios increased when there was a switch from Iron to Alu heads or the reasons for engines making more power with low temp thermostats and higher efficiencies with higher temperature stats.
As a general rule more heat trapped in the cylinder is good for efficiency but bad for controlling detonation and abnormal combustion at high cylinder pressures.

That engine may actually be an illustration of the issue, to me what he is making is not insane power considering it is a 3l engine on E85 @35psi boost. The fact he is down at 7.5:1 is testament to the heat/detonation issue with E85 he could be a lot higher than that.

As a yard stick I work with a 2.8l 6 cylinder of similar design, 9:1 CR on normal road fuel equivalent to US91, ~19psi and 630hp at the crank (about 550 at the hubs). A similar 2.8 on E85 was pushing over 950hp a few years back without an internal coating in sight.

Side note - Now coating inlet ports and the back of inlet valves may be a good plan as it will help keep the incoming charge cooler.
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
Rhinoman
contributor
contributor
Posts: 256
Joined: Thu Sep 24, 2015 2:14 pm
Location: Wiltshire, UK

Re: Piston coating

Post by Rhinoman »

kb1gtt wrote:
Mon Sep 10, 2018 4:29 pm
I recall Teflon coating as well. Theory being that it's a great dry lubricant, so it helps keep things from sticking to the top of the piston and prevents these ridges from poking thought the boundary layer. The results are colder crown temperature.
DuPont, the inventors, have stated that Teflon is not suitable for use in an internal combustion engine.
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Re: Piston coating

Post by kb1gtt »

I believe DuPont also says it's OK for cooking pans. I'm fairly sure they simply tell you want ever they think the market wants to hear. AKA if the market has small profits, they might as well do the CMA thing. However if it's a large profit like cooking pans, they don't care.

Also of course OEM car's tell you that replacing the intake with an aftermarket intake voids the warranty. Yet people do it anyhow. It's easy to find people who will say to not do something. It's harder to find out what happens if you do something. I wonder, does the coating disappear? Does it or does it not make your boundary layer more robust and allow for higher combustion pressures, etc. It's harder to find those kinds of information.
Welcome to the friendlier side of internet crazy :)
Rhinoman
contributor
contributor
Posts: 256
Joined: Thu Sep 24, 2015 2:14 pm
Location: Wiltshire, UK

Re: Piston coating

Post by Rhinoman »

Its OK in cooking pans as long as you don't use anything metal in them. I can't claim to do a lot of cooking but in my experience when its not a top quality pan it scratches quite easily and can peel.
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Re: Piston coating

Post by kb1gtt »

Yup, it kills birds, but it's apparently OK for humans as it only causes flu like symptoms in humans, so that's OK. I'm not sure how that effects babies, as those are half way between a bird and full sized human.
https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety

The claim is that the more nasty PFOA's are removed during the manufacturing process, so the out gassing at normal cooking temperatures is not a health hazard. I would expect the same from a coated piston. If the concern isn't health related, then Dupont's concern is likely finical. AKA if the coating doesn't last 100kmi (160kM) then they wouldn't want to suggest it's use. I've seen some guys pushing 1000kHP from Cummins V8 which normally did around 0.25kHP. They mill out some emissions related high points off the top of the piston to make it smoother, and with less protruding features. This helps maintain the boundary layer. They also Teflon coat the top to help keep stuff from sticking to it. The claim is that it prevents the boundary layer from breaking down. I doubt it would last as long as an OEM would need, but for racing it seems to last long enough. About the health concerns, when your dumping out huge amounts of un-burnt fuel, a known carcinogen, then I would guess the questionable Teflon out gassing isn't a huge concern.
Welcome to the friendlier side of internet crazy :)
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

There is also a question of how the outgassing of the teflon reacts in an environment full of combustion end gas.

Those PFOAs might not last long in an atmosphere of NOx, CO, CO2, HC and H20 at a few thousand Kelvin. At the temperatures and pressures in a running engine unusual chemistry can happen, obvious example is the normally stable nitrogen in the air becoming unstable and forming NOx,

A quick SAE paper search: oil additive testing says "any flourine compounds would be in a semi-volotile form (not gaseous or solid ash)"
"only one sample revealed a trace amount of hexafluropropylene @77 particles/billion" (Technical Paper 941983)

There's not much out there for combustion of teflon in cylinder but oil additive work would suggest that most of it is utterly destroyed by the cylinder temperatures.

Edit - Pretty much if that double fluoride bond on the PTFE can be broken by the in cylinder conditions then I would expect it to just become CO2 and Hydrofloric acid but in such trace amounts that it is insignificant.

Given that pistons are in the 200 degrees range at 1mm below the crown without oil cooling jets then the teflon is going to be marginal, probably subliming and likely gone within the first few hard pulls. With cooling jets it might last longer?
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
User avatar
kb1gtt
contributor
contributor
Posts: 3758
Joined: Tue Sep 10, 2013 1:42 am
Location: ME of USA

Re: Piston coating

Post by kb1gtt »

I understand that Royal Purpose uses as a dry lubricant which creates lubrication properties while the coil has gone away. I once heard a vague claim that was a Teflon compound which they some how got to remain suspended in the oil, and bond with the metal when the oil went away. Does anyone know the nitty gritty details about this Royal Purple lubricant thing? Is there any chance that might shed some light into the use of Teflon out gassing issues?

When I heard the claim I'd consider it to be from non-creditable sources. AKA some drunk guy in a garage telling stories.
Welcome to the friendlier side of internet crazy :)
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

There are lube additives containing teflon, slick50 is one, not quite sure how any of them would "stick" teflon to the metal of the engine, what with it being one of the most non-stick compounds we have... :lol:
So that bit is probably bullshit.

That SAE paper was from 1994 so it has been about in concept for a long time. In most cases they will have little effect assuming the hydrodynamic lubrication is maintained. Where they could have use is stopstart and people with a tendency to rev cold engines.
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
Rhinoman
contributor
contributor
Posts: 256
Joined: Thu Sep 24, 2015 2:14 pm
Location: Wiltshire, UK

Re: Piston coating

Post by Rhinoman »

OrchardPerformance wrote:
Tue Sep 18, 2018 8:07 pm
There are lube additives containing teflon, slick50 is one, not quite sure how any of them would "stick" teflon to the metal of the engine, what with it being one of the most non-stick compounds we have... :lol:
So that bit is probably bullshit.

That SAE paper was from 1994 so it has been about in concept for a long time. In most cases they will have little effect assuming the hydrodynamic lubrication is maintained. Where they could have use is stopstart and people with a tendency to rev cold engines.
Google for ftc v quaker state oil company, the ftc won and all the claims made about slick 50 were proven false
Simon@FutureProof
contributor
contributor
Posts: 413
Joined: Tue Jul 24, 2018 8:55 pm
Github Username: Orchardperformance
Slack: Orchardperformance

Re: Piston coating

Post by Simon@FutureProof »

https://www.ftc.gov/news-events/press-releases/1997/07/quaker-state-subsidiaries-settle-ftc-charges-against-slick-50

Still on the FTC site.

I would assume some big manufacturers and oil refiners were the ones that brought that one to the FTC...

Not saying slick50 works but certainly that SAE paper shows a reduction in wear when using PTFE as an additive and they are peer reviewed papers. I guess the claim of wear reduction has to have a baseline and if that baseline is a stock mineral oil with no dry lube additives of any kind (zinc, molly disulfide, etc, etc) then the reduction could be dramatic. However if your using a mineral oil with no additives then you need your sanity checked. :lol:
I will take another look at that SAE paper and see what they compared the PTFE treated oil against, didn't look too hard as I was only looking at the emissions implications.

Most modern oils have very good additive packages that make aftermarket additives pointless in most cases, the only time you might want to consider them is for highly strung race engines with no catalysts as most of the best dry lubes poison catalysts and lambda sensors in high quantities, that is why you will see "not for road use" on a lot of racing oils. (and kind of why some racing oils exist).
I know you can buy some effective zinc based additives for use on highly loaded flat tapped cam engines, modern oils tend to avoid zinc for the above reason but it works well on flat tappets.
Now keeping MRE in stock in the UK - https://www.FutureProofPerformance.com
Post Reply