I never would have believed you could get those kind of resultsfrom a glorified paint job. With those words, another skeptic(in this case, a NASCAR Winston Cup engine builder) had come toaccept the value of special coatings applied to engine components.
At the time, such skepticism was not totally unwarranted. Likeany emerging technology, the coating of metal parts, with fluoropolymer,metallic/ceramic and graphite materials underwent a painful teethingprocess before it was perfected. But the worth of various coatingprocesses has been repeatedly proven over the past 10 years, sodoubting Thomases and Thomasinas are out of step with reality.
Even Ford and General Motors have embraced the process with bothcompanies using coated pistons in some applications. A major supplierof aftermarket engine components has also embraced the worth ofcoatings and offers pistons with moly-based, graphite-coated skirtsfor a wide variety of engine types.
If there’s a rub with friction reducing and heat blocking coatingsit’s their time and expense. Although most applicators offer quickturnaround, shipping usually takes at least one day each way.If time isn’t a major stumbling block, additional expense maybe the hurdle that can’t be jumped.
Like your gas mileage, prices vary, but custom coating a set ofpistons and bearings can add substantially to the cost of rebuildingan engine. Charges of $10 to $40 per piston, $5 to $10 per valveand $40 for a set of bearings, plus shipping charges, are notunusual.
When customers are receptive to those additional costs, an enginerebuilder’s life becomes somewhat easier because engines withcoated components demonstrate greater durability and occasionallygenerate more power. But in price-competitive environments, sellingthe worth of coatings can be difficult.
With the recent advent of do-it-yourself coatings, cost considerationsmay diminish dramatically. But proper coating of engine partsis a bit more involved than simply spray painting, so in-housecoating operations may or may not be viable. The performance ofcoatings also varies significantly according to their compositionand the applicator’s capabilities and experience.
New applicators will have to learn to avoid the same pitfallsthat initially earned coatings a reputation for poor performance.In the late 1960s and early ’70s, when coating technologywas in its embryonic stage, applicators were still experimentingto a large degree. Many didn’t understand coating and base materialcompatibility issues, nor did they realize that proper preparationis vital to adhesion. Consequently, coatings cracked, flaked off,didn’t perform as advertised, or even all of the above.
Most commercial applicators are religious in their adherence topre-coating preparation techniques that leave a component surgicallyclean. Some applicators use a five-step cleaning process thatincludes the application of heat along with mechanical and chemicalcleaning. After the parts are sprayed, they’re cured in an ovenat between 350 to 500F.
Similar techniques are used by virtually all commercial applicators;in-house coating operations must also adhere to the "cleanlinessis next to Godliness" gospel to achieve success. The logicalquestion is, therefore, what benefits do coatings offer to justifythe trouble and expense?
Although claims and speculation abound, there’s little documentationavailable to provide substantial proof of significant power increasesderived from anti-friction coatings. A principle advantage ofsuch coatings is that they’re dry film lubricants and provideback-up lubrication in the event engine oil is absent. Secondly,since they retain engine oil under conditions of extreme heatand pressure, they offer an extra margin of safety in the eventof oil starvation. These types of coatings are typically appliedto piston skirts, bearings, valve springs, camshafts and lifters.
Builders of professional-level race engines were among the firstto use coated parts extensively. The extremely high loads underwhich these engines operate make them prime candidates for failuresarising from scuffing and galling of internal components. In manyinstances, coatings are used as a means of extending a component’suseful life even when hard failures are rare.
As one sprint car engine builder stated, "I won’t installuncoated pistons. The coated ones look so good when they comeout of an engine it’s hard to believe they’ve been run for morethan a race or two. We’re now able to use a set of pistons fora whole year and that really cuts down on maintenance expense."
For many production engine rebuilders, such considerations maybe irrelevant because a quality rebuilt engine can now run formore than 100,000 miles – far longer than a typical consumerexpects. But for rebuilders who deal with fleets and stationarypower plants, where durability expectations are high and closelymonitored, measurable improvements in engine life can lead toincreased customer loyalty and satisfaction.
On the surface, taking steps to increase engine life beyond customerexpectations may seem like biting the hand that feeds you. Afterall, shorter times between overhauls translates to more business.From a myopic perspective, that’s true. But when viewed throughcorrective lenses, a more ethical and ultimately more profitableviewpoint comes into focus.
People tend to talk, especially to other people in similar professions.When one fleet manager converses with another and finds his enginesneed to be rebuilt more frequently, he just may decide to takehis business elsewhere. Similarly, if your customers’ enginesare enjoying above average life spans, word is likely to spread,resulting in new customers and increased profits.
Metallic/ceramic thermalbarrier coatings applied to the exhaust headers provide two advantages. They protect the headersfrom rust and corrosion and reduce heat loss which translates into high poweroutput. Thermal barrier coatings are also applied to piston crowns, combustion chambers, intake manifolds and exhaust parts.
In addition to dry film lubricant-type coatings, oil sheddingcoatings are also available. Like the Teflon® used to createnon-stick frying pans, oil shedding coatings resist the adhesionof fluids to their surface. Many race engine builders spend agood deal of time and money attempting to minimize the power lossesassociated with oil windage in the crankcase. Coating connectingrods, crankshaft counterweights and windage trays with a non-wettablecompound enables oil to leave the premises quicker. Since it hasless time to hang around in the way of a spinning crankshaft,engine oil interferes less with the creation of horsepower.
Another area in which non-wettable coatings can be found is theintake tract. Some engine builders coat intake manifold plenumsand runners in an attempt to reduce fuel puddling and reduce surfacefriction.
Applyingdry film lubricant coatings to main and rod bearings adds an extra measureof insurance against damage caused by oil starvation. Reduced friction is another benefitthat offers horsepower and durability improvement potential.
Many of the power-enhancing effects of friction reducing and oilshedding coatings are highly debatable because their effects arerather subtle. Everything else being equal, the difference betweentwo engines, one assembled with coated components, the other without,may only be a few horsepower. But many engine builders have foundthat coatings allow them to make other changes that deliver moresignificant power increases.
As an example, coated bearings typically allow tighter clearanceswhich in turn mean reduced internal oil hemorrhaging. With lessoil slipping out between the crank journals and their bearings,adequate oil pressure can be maintained without the need for ahigh pressure oil pump (and its attendant parasitic power loss).
Obviously, many of the benefits derived from friction reducingand oil shedding coatings are most applicable to hard core raceengines. Metallic/ceramic coatings (silicon and zirconium based)are more universally beneficial. The most popular use of thesetypes of coatings is on exhaust headers, where they provide atwo-fold benefit.
When headers are coated, they don’t transfer heat as quickly soexiting exhaust gases stay hotter and maintain higher velocities.That improves engine efficiency because less residual exhaustgas in the combustion chamber leads to a reduction in intake mixturedilution. In turbocharged engines, higher exhaust gas temperaturesequate to more boost and higher power output.
Secondly, with less heat transfer through the header tubes, theengine compartment stays cooler so the incoming intake chargedoesn’t have its temperature raised as much as it would were theheaders not coated. For racers working on hot engines, coolerheaders mean fewer burnt fingers.
Then there are the cosmetic considerations. Being constructedof mild steel for the most part, exhaust headers have a markedtendency to cultivate a layer of iron oxide on their exterior.Metallic/ceramic coatings won’t rust, so coated headers maintaintheir appealing appearance longer. Most headers are coated insideand out as a means of sealing out rust, but the interior coatingalso improves durability because it reduces the thermal shockof hot exhaust assaulting the steel.
Inside an engine, metallic/ceramic coatings are frequently usedon piston crowns and valve heads to reduce heat transfer and itsattendant power losses. A metallic/ceramic coating material, specificallyformulated for high temperature applications, can withstand typicalcombustion chamber temperatures even though they’re only .001"to .0015" thick.
In addition to keeping heat in the chamber where it can producepower, metallic/ceramic coatings, by virtue of the fact that theypresent a barrier to heat transfer into a piston, reduce skirtexpansion. Some engine builders have found enough of a differencein skirt expansion to allow a tightening of piston-to-wall clearances.
The underside of a piston with a coated crown speaks volumes aboutthe effectiveness of thermal barrier coatings. After any lengthof service, the underside of an uncoated piston typically hasa brownish color to it, like the inside of an aluminum pan thathas been used for frying. The underside of a coated piston looksbrand new because it didn’t cook any of the engine oil that contactedit.
Many engine builders have clearly documented significant horsepowerincreases resulting from the use of metallic/ceramic coatings.The effect is greatest when piston domes, aluminum cylinder headcombustion chambers, exhaust ports and headers are coated. Measurablepower increases should result from the application of metallic/ceramiccoatings because regardless of the method, the payoff for maintainingcombustion heat is more power.
Frequently, the amount of spark lead required for maximum poweris less when thermal barrier coatings are used. One caveat doesexist, however. The use of thermal barrier coatings in some engines,particularly those with cast iron heads, may lead to detonationbecause too much heat is retained.
Should you decide to experiment with coatings, you can purchaseaftermarket replacement parts that have already been coated, contacta commercial coater or try the do-it-yourself route. Tech LineCoatings & Lubricants and Extreme Performance Coatings bothoffer a variety of coating materials suitable for do-it-yourselfapplications. These materials are typically applied with an airbrush and can be cured in a home oven. The air supply to the airbrush should be filtered to remove moisture and any other accursedforeign elements.
Curing temperatures vary according to the composition of the componentbeing coated and the coating material. As a general rule, aluminumparts are cured at 350 F and iron parts are heated to 425 F; metallic/ceramicheader coatings usually require curing at 500 F. Usually a bakingtime of one-half hour to an hour is specified. But, coatings canbe allowed to air dry; a running engine provides the heat forcuring after the component is installed.
Custom coatings are usually sprayed on a component with an air brush. Carl Bentonof Polymer Dynamics is shown here coating a piston. Note that Benton is wearing the necessarysafety equipment, i.e., safety glasses and a mask protect him while rubber gloves protectthe part being coated. Finger oils can interfere with proper adhesion of the appliedcoating.
Virtually all types of coatings, including thermal barriers anddry film lubricants, are available for do-it-yourself application.As opposed to the coatings used by commercial applicators, thematerials sold by Tech Line and Extreme Performance are largelywater-borne as opposed to solvent borne. The latter-types of coatingscannot be cured in a standard oven because of the hazards associatedwith solvents.
As might be expected, inhaling any of the mists or fumes thatare part of the coating or curing process should be avoided. Water-basedcoatings don’t emit any harmful fumes during curing, but somemist undoubtedly fills the air during a spray application. Theproper protective equipment should be worn when any coating materialsare applied. Extreme Performance Coatings offers some coatingsthat can be brushed on, thereby eliminating concerns associatedwith inhalation of a spray mist.
Prior to the actual application of a coating, a part must be absolutelyclean. A light, low pressure sand blast with fine aluminum oxideor sand is recommended. Blast pressure should be set to 30-40psi in a siphon-type sand blaster.
The question of the day is, of course, whether self-applied coatingsare of the same quality as those that are commercially applied.Answers vary according to the allegiance of the answerer. Commercialapplicators obviously view the integrity of self-applied coatingswith skepticism and disdain. Representatives of companies sellingcoating materials see things in a somewhat different light.
Objectively, the nature of the application and the volumes involvedwill determine whether commercial or self application is mostadvantageous. But irrespective of application method, coated engineparts appear to have a silver lining.