If you were to place technological advances on a scale, I would say that engine coatings would probably rank near the top. Engine coatings have a lot of merit, but unfortunately are often overlooked.
Engine coatings have a reputation that they are only beneficial for racing applications. Yes, coatings are regularly applied and highly appreciated in professional racing and for good reason – the advantages are incredible. However, the benefits given by coatings can be useful to the average engine builder or the weekend warrior as well.
The major misconception is that coatings provide horsepower. While coatings do reduce friction, which in turn frees up horsepower, the major attribute is insurance. The primary function of engine coatings is to provide longevity and stability at a very reasonable cost.
When I think about engine coatings, the first thing that comes to mind is a NASCAR engine. Let’s put the NASCAR engine into perspective for a moment. Its 358 cubic inches make 900 horsepower at 9,000 rpm for 500 miles. Inside these engines are many intricate parts used to reduce mass and reciprocating weight. So the pieces of this powerplant have to be strong, light and be able to take a beating and survive. Coatings offer the cushion, stability and strength to make all these parts harmonize like a symphony. And let’s be honest: 900 horsepower is music to any gearheads ears.
There are different coatings for different components of the engine and they can be broken down into different categories for their purpose. To understand coatings we will take each component of the engine and describe the processes it can undergo for treatment.
Let’s start with the block. In most cases, the engine block is very porous. Back in “the day,” engine casting was crude, leaving debris that could come loose and find its way into the oil pan. Because there were no aftermarket blocks, most race shops would spend hours of polishing the inside of the engine block in areas such as the lifter valley, timing chain and the underside of the piston skirts above the oil pan rail. The polishing and grinding would clean and seal the pores of the cast block.
But, there is an easier way that is practiced today, which is less time consuming and much cheaper. Simply paint these areas of the block with a lead-based epoxy paint such as “Glyptal.” Once the block is machined, clean it well with a non-petroleum-based solvent and tape off the lifter bores and other areas such as the timing chain face of the block and coat with paint. This will seal off the pores of the block and hold up very well under harsh conditions.
For the crankshaft, there are a couple of different options depending on the material. If the crankshaft is cast iron the best process is to have the crankshaft counterweights coated with an oil shedding coating. If the crankshaft is billet or forged, it is best to use a process known as micropolishing. Even though the crank’s surface may look nice and smooth, under a microscope it can still be very rough. The micro-finishing process smooths the surface peaks and eliminates the rough edges making the entire crankshaft look as though it has been polished. The microfinishing process will allow oil to sling off of the counter weights reducing parasitic drag. A cast crankshaft cannot be micropolished because the process tends to open up the pores of the casting producing stress risers, which can cause the crankshaft to fail. The same process is used for the connecting rods also. It’s all about what kind of material they are made from.
There are no coatings used on the camshaft. Because of the loads placed on the camshaft, the coating would eventually lose contact with the surface leading to failure. However, the camshaft can be micropolished as well. Even if the camshaft is a roller that looks very smooth and slick, a closer look usually reveals a rough surface finish also. A flat tappet camshaft is typically rough when you get it out of the box and looks as though it needs a polishing anyway. The micropolishing process eliminates any high spots and helps to stress relieve while improving surface finish.
Remember, the lobes of the camshaft need to remain somewhat porous to retain oil, so the lobes should not be polished like a mirror. One thing often overlooked is roughness of the camshaft under the microscope. By improving surface finish you reduce vibration in the valve train which in turn makes more power and creates longevity of the moving pieces.
For the rest of the valve train there are some different options. If your lifters are made of billet material then they can be coated with a DLC (diamond like coating). DLC is very hard and scuff resistant, which offers a lower coefficient of friction, which reduces oil temperature and wear. If the lifter is a roller it will need to be disassembled before the DLC process. There are only certain brands of lifters this can be done to. In order for the DLC to be applied, the lifter body needs to be micropolished first in preparation for the DLC. For all other lifters there are no coatings that will withstand the loads and would diminish with time. Remember this: the DLC is a one-time coating. If you were to tear the engine down for a refresh you cannot have the DLC applied again.
Valve stems can be coated with chromium nitride, a metallic coating that offers a slick, low coefficient of friction to help reduce heat in the valve guides. The chromium nitride is more forgiving and will wear as there is surface contact but can be re-applied when the engine is freshened up. The DLC is hard like an egg shell and will not wear like the chromium. It will crack and score the surface if there is a problem.
On the face of the valves and the combustion chamber of the cylinder head a thermal barrier coating is applied. The object is to keep heat in the combustion chamber, but when there is too much heat, power goes away.
By coating the face of the valves and the combustion chamber along with the exhaust runners with a thermal barrier coating, heat can be transferred out of the engine into the exhaust headers for more exhaust velocity. This works great if the header or manifold is coated also. The intake runners of the cylinder head along with the runners of the intake manifold can also benefit from a thermal barrier coating. This reduces heat of the intake charge along with increased port runner velocity. The underside of the intake manifold can be coated also to help reduce heat from oil splash from the lifter valley.
There are no viable coatings available for the valve spring retainers. The only surface of the retainer used is the underside, which is not a good surface to coat regardless of the material. The retainers can be micropolished, which could provide a smooth surface but this has not been shown to offer any gains. The springs can also be micropolished, which will reduce stress risers in the coils reducing friction; especially in the use of multi-spring applications where the coils come in contact with each other. The biggest gains in micropolishing springs have been found in the spring rate consistency over a period of time.
Although the valve locks can be DLC coated the rest of the valve train, such as the pushrods and rocker arms, do not see any advantages of any coatings. The only rocker arms that need to be coated are stock-type stamped rockers where the face of the rocker arm will slide across the top of the valve stem.
The tops of the pistons will also benefit from a thermal barrier coating. Over time, the material of the piston will become soft causing the top piston ring to collapse. The thermal barrier coating will produce better heat dissipation from the flame front keeping heat in the combustion chamber and out the exhaust port rather than in the crankcase. For the skirts of the piston there is a PTFE based coating that reduces scuffing. The coating is very porous which helps in retaining oil. This offers reduced friction, temperature and wear, along with the elimination of dry starts. This type of coating is very similar to what is used on the engine bearings and offers the same benefits.
Wristpins are also coated with a DLC. The wristpins live in a harsh environment receiving very little oil and subject to extreme heat. The DLC helps eliminate the friction to reduce wear in the wristpin bores offering lower coefficient of friction, reduced oil temperature and longevity.
There are several facilities worldwide that offer engine coatings and you will find that they are reasonably priced. Most coating facilities offer processes for differentials and transmissions also. Whether the engine is stock, used in an industrial application, or used for racing, if your customer plans on keeping it or enjoying it for a period of time, the benefits of coatings will far outweigh the cost. n
Thanks to Calico Coatings (www.calicocoatings.com) for the assistance with this article and photos.