More than a five-cent solution to cylinder distress
Innovators seldom have an easy time of it. In the notoriously conservative general aviation world, advances often are met with a steely glare and pursed lips. "Gee, I don't know if that's going to work" might be the first words from a prospective customer's lips. Followed by "We've never done it that way before." Getting a foothold with a new idea, unusual kind of material, or out-of-the-ordinary method is as easy as climbing a Vaseline-covered rope.
Engine Components, Incorporated, in San Antonio, Texas, knows the slippery side of innovation all too well. As the company that brought the Cermicrome cylinder-wall plating process to the United States in 1987, ECI has grappled the cords of success and been nearly hung by the rope of miscues. (For more on the ups and downs of Cermicrome, see " Whither Cermicrome?.")
Today, however, the company is flying high, rolling out what appears to be a successful new process that will make general aviation proud. Called CermiNil, this new nickel-silicon treatment promises to make cylinder bores corrosion-resistant without the headaches of chrome plating. This would solve one of the major problems for owners of seldom-flown airplanes. In a perfect world, we'd all fly several times a week. The frequent use would prevent rusting of the bores and subsequent damage on the next start-up. But few operators fly that often, so over the years a number of cylinder- wall treatments have been put forward to stop corrosion. Among the most popular is chrome. The material actually does two things: It prevents barrel corrosion, and it allows the bores to be plated with sufficient thickness to give a new lease on life to worn-out barrels- -those too large in diameter or out of round from wear.
Chrome plating has a spotty history, however. It doesn't conduct heat as well as steel cylinders, and it's notoriously difficult to break in properly. In addition, plain chrome is not oil wettable, so channels must be forced into the surface to hold oil. Chrome is also a real black art for the applicator; to do the job correctly you must have the proper techniques, backed up by the right combination of chemicals.
Engine Components had been dealing in channel chrome for some years when the Cermicrome process — basically a silicon- carbide slurry that's honed into otherwise normal chrome bores — came to America. ECI licensed the innovation from the British company Laystall Limited.
Now, however, comes CermiNil, a wholly different kind of treatment that utilizes a nickel and silicon film deposited onto the cylinder bore. Unlike Cermicrome, which had a surface volume of around three percent, CermiNil is contiguous. And unlike a nitrided layer — a popular OEM tactic — the CermiNil coating is substantially thicker.
While CermiNil is new to airplanes — and ECI's particular implementation of the process is itself unique — the nickel- deposition concept has been in use by European automobile manufacturers for decades. It's still popular today in a wide range of engines. Is it tough? Consider the power produced by the latest Porsche 911 Turbo powerplant — more than 400 horsepower from a mere 3.6 liters, or about 220 cubic inches. That air-cooled engine uses Nikasil (a trade name for the nickel/silicon impregnation) bores. In aviation, Rotax's 80-hp 912 and 115-hp 914 four-strokes use Nikasil liners, with good results so far.
Among the widely touted advantages of the nickel-silicon treatment are corrosion resistance, improved heat transfer, better uniformity, and excellent overall durability. Moreover, the method also promises to be easier to break in than chrome and Cermicrome. Will CermiNil work wonders in the aviation world? While there are too few CermiNil cylinders in circulation right now to say definitively, initial results look promising. In addition, the process lends itself to better quality control than chrome.
Yet another advantage, for ECI at least, is the CermiNil process's much less toxic makeup. Chrome plating uses highly toxic chemicals; the runoff must be treated so that a hazmat service will even pick it up. CermiNil is much more friendly to the environment.
Before any plating can be applied, however, a cylinder must first run the ECI gauntlet. The list of services available reads like a menu in a Chinese restaurant. You can have everything done to your cylinders, or services a la carte. When it's received in San Antonio, the cylinder is inspected and the requested services are recorded on cards and bar-coded paperwork that will follow the jug through the entire process. Then the cylinder goes into a heating jig that applies about 450 degrees Fahrenheit to the top end; this allows the aluminum head and steel barrel to be unthreaded; much of what keeps the heads from working on the barrels is their interference fit. (The relatively low temperature required to loosen this grip should make you wary of operating any air-cooled engine near the allowable maximum cylinder-head temperature.) Once demated, the barrel goes into a box — to be inspected, repaired, and recycled. Normally, when you send your cylinders to ECI, you are guaranteed to get your head back, but not the sleeves; the exception is if you ask for exchange heads to save downtime.
Then the heads go into the inspection area, where dye penetrant detects any cracks. Skilled technicians then grind the material out to the bottom of each crack identified. The next step is welding, where any material removed is then replaced by using a special welding process. According to ECI, the company has invested heavily in finding the right welding alloys to integrate best with the head castings. Then, if you opt for ECI's Freedom process, the heads are heat-treated. By heating the head with the welds in place, any intragranular tension is supposedly released, vastly improving the metallurgy of the head and helping to prevent future cracking. (It's worth noting that many industry experts cringe at any welding of cast parts.) Finally, machining is performed to return the head to original dimensions and to correctly position critical points, such as the valve guides and spark-plug holes.
With ECI, you can choose to have your now-refurbished cylinder head mated to a reworked barrel or to a new forging, which ECI constructs on premises. Inside this barrel you can have conventional steel — the ECI forgings are through-hardened, meaning that the hardness is not just on the inner surface — as well as Cermicrome or CermiNil. You can even ask for plain old channel chrome, if you prefer.
Compared to the medieval chrome-plating department, the CermiNil line is clinically clean and refreshingly peaceful. Once demated from the cast-aluminum head, a cylinder sleeve receives several steps of cleaning solvents and then moves among seven stages until the film deposition process is complete.
Finally, the completed barrel goes into a manual honing machine — operated, according to ECI management, by men who must have just the right touch — for final dimensional grinding and application of what's called the ring finish. This is simply a crosshatch scored into the material to promote ring break-in. Next, the barrel joins the now crack-free and stress-relieved head casting. If you have opted for the complete cylinder package, then new seats, valves, and rocker arms and bushings are installed. As mentioned, you can have ECI do as little or as much of the work as you'd like.
What's the price? ECI introduced CermiNil at the same price as Cermicrome, even though it's a slightly more expensive process. At press time, the full CermiNil cylinder treatment — including new pistons, rings, valves, guides, rocker-arm bushings, and other related hardware — for a parallel-valve Lycoming was around $750, about one-third less than a factory-new cylinder. If you need your cylinder back in less than the normal 10-day turnaround, you can get an exchange cylinder kit for an additional $50. If your cylinders are in really good shape to begin with and you have the facilities to insert new seats and guides, you can have ECI do just the basics — inspect and weld cracks, heat-treat, and CermiNil — for $250 on that same Lycoming cylinder. Continental, which has been extremely aggressive in pricing factory-new cylinders recently, offers replacements for marginally more than a CermiNil job.
If you go for the full-house treatment, about all you'll have left over from your original cylinders is the head casting. (And it's some consolation to know that, unless you specify otherwise, they're your own cylinder heads coming home to roost.) It's not too much a stretch to think that ECI is one major component away from having all-new cylinders available. Which wouldn't be too far-fetched for a company willing to take risks — and innovate.
Whither Cermicrome?
What happened to this miracle treatment?
In 1987 Engine Components licensed the silicon-carbide impregnation process it calls Cermicrome, and a few short years later the bottom seemed to fall out. Owners across the country began complaining about early top-end problems — rising oil consumption, falling compression, and increasing blow-by. Some of these symptoms occurred in low-time engines. Basically, the Cermicrome treatment had been worn away at the top portion of the piston travel. In no time, the untreated chrome section, now unable to wick necessary oil into place, wore through to the untreated steel below. Infant cylinders began coming back looking like high-time thrashers.
By the summer of 1994, word of the trouble had spread and Cermicrome's reputation was mud. Seeing the sales fall off and hearing overhaul shops beginning to recommend other treatments, ECI undertook a study to find out what had gone wrong.
ECI's director of engineering, Jimmy Tubbs, looked into all the possibilities, including subtle changes in the silicon-carbide material, applications procedures, effects of using different oils in the field, and piston-ring quality. Tubbs found that the Cermicrome hadn't changed much as it was applied to the cylinders, even though subtle process changes had taken place at ECI during the period. In addition, Tubbs noted that the underlying chrome hardness through the period was consistent and that there didn't seem to be any difference in Cermicrome treatments between cylinders that made it to TBO and those that died prematurely.
ECI's focus then fell to the piston rings. Eventually, the company discovered that during a five-year period, the ring manufacturer had gradually changed the allowable limits of certain ring metals. Of importance, the range of "acceptable" hardnesses had increased dramatically in the K14 model rings that ECI was recommending for use with Cermicrome. Tubbs surmised that some rings were manufactured with a hardness exceeding that of the Cermicrome-treated cylinder bores. No surprise, then, that so many cylinders suffered premature failure and extraordinary ring stepping.
Unfortunately, without testing it's impossible to know where in the hardness range any set of rings falls. It's also possible that you might have five of six cylinders with the "normal" hardness rings, and the sixth with rings of abnormally hard compound.
ECI's solution was to undertake producing a ring of its own, a copy of the nearly ancient AMS 7310 iron ring. This is a simple ring metallurgically, but it has proven to be quite compatible with the Cermicrome process. (Why not use it in the first place? ECI took the recommendation of the Cermicrome patent holder and went with the K14 ring because it's less prone to breakage than the old 7310.) Now every Cermicrome-treated cylinder set that leaves San Antonio goes with ECI's own ring pack. Shipping of these rings began in December 1994.
For owners facing possible early top-end distress, the bad news is that you may never know whether the set of K14s in your engine is of the right specification. On a more positive note, ECI claims to be working to fix any instances of premature failure found in the field. What's more, as of December 1995, ECI had yet to find a single instance of early failure with the 7310 rings. In his report, Tubbs concluded that "...the time frame in which the AMS 7310 rings have been in operation has not been long enough to declare total victory over the premature wear problem. However, the results obtained are very encouraging." — MEC
Case Closed
ECI does more than top ends
If you thought ECI was all about cylinders, think again. The company has expanded its line of bottom-end services and will push out further still into the area of accessory overhaul. For now, the company can perform the major case-fixing tasks called for at the overhaul.
Lapping and line boring are two of the most common procedures. Lapping grinds the mating surfaces of the cases so that they are true and flat, while line boring is the process of cutting the main bearing and camshaft journals back to round. It's worth noting that ECI welds the pivots of the accessory gears and cuts new holes to compensate for the material taken from the case halves; not all shops do this, and there could be problems with accessory-gear lash as a result.
As with the cylinder heads, ECI can weld most cracks and apply factory-authorized modifications, like the Continental seventh-stud alteration. Lycoming owners can have their cases treated with the stress-relief Freedom process; ECI does not perform this process on Continental cases.
For crankshafts and camshafts, ECI will inspect and regrind to specs, applying a new hardness layer to the components from its in- house nitriding tank. ECI is also planning to start crankshaft balancing services soon. As part of the crank service, ECI plates, polishes, and dimensionally inspects incoming cranks; you can even have the firm install new counterweight bushings and perform ultrasonic inspections.
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