Nickel Bore Rejuvenation Kit

• Engine Components, Inc.’s Exclusive Nickel/Silicon Carbide Composite Coating
  
• Reliable
  
• Resists both Corrosion and Wear

» Nickel Bore Rejuvenation Kits
» Diamond Honing
» Micro Honing
» Ring Face Materials and Geometry

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Nickel Bore Rejuvenation Kits

Nickel Bore Rejuvenation Kit Includes: ECi Honing Tool™; ECi Diamond Honing Stones™; ECi Micro Honing Brushes™; Cotter Pins; Spray Bottle; Funnel; 1 gal ECi Honing Oil™.

ECi introduced the CermiNil™ process to the general aviation market in 1994. Since that time, ECi has produced in excess of 100,000 cylinder bores with the CermiNil™ process.

With many of these cylinders reaching TBO, ECi has been receiving an increasing number of reports that many of these bores are within serviceable limits when removed at TBO. Along with these reports, ECi has received numerous requests for information asking for instructions as to how to hone the cylinder bores prior to placing the cylinders back in service.

In order to respond to these requests from the field and recognizing the complexity of the system comprised of a CermiNil process bore, a ring set, a piston and the lubrication element, ECi has developed and recently introduced a Nickel Bore Rejuventation Kit™. This kit includes all the necessary instructions for processing a dimensionally serviceable bore as well as all the materials needed to accomplish the re-processing.

The CermiNil process is dramatically different from any other bore surface used in aircraft piston engine cylinders. There are several steps and elements which must be understood and accomplished prior to the successful rejuvenation of a CermiNil process cylinder bore. The information on the inside of this brochure explains the details associated with diamond honing, micro honing, ring face materials and geometry, all of which are essential elements of CermiNil process rejuvenation.

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Diamond Honing

Metal bond diamond (industrial diamonds held together in a nickel plated matrix) honing has been around for some time and has been widely adopted by the automotive industry because it is well-suited to high volume production lines. Diamond stones cut faster, last longer and cost less on a per hole basis than conventional stones.Production of aircraft piston engine cylinders has traditionally not used diamonds because of the low volumes and the insignificant cost associated with honing using conventional abrasives. Up untilthe introduction of the CermiNil process by ECi there was no reason to look for alternate honing methods.

Due to the composite structure of the coating produced by the CermiNil process (10% silicon carbide particles in a hard nickel plated matrix),it was quickly discovered that conventional abrasives such as bonded silicon carbide and aluminum oxide could not efficiently cut the composite material. By trial and error, it was learned that metal bonded diamond used under controlled conditions did an excellent job of honing to size CermiNil processed bores that had first been rough ground with a metal bonded diamond wheel.

Metal bonded diamond honing stones, however, create one major problem (besides their very high initial cost) which must be remedied. Due to their inherent cutting action, they tend to leave a lot of folded and torn metal on the surface after honing. A diamond honing stone literally rips and tears chunks of metal away from the bore surface which is great for removing lots of material quickly but not so great for producing a smooth, clean, plateau-like bore finish which is compatible with the ring face.
The quality of the surface finish left by a diamond honing stone obviously depends on the grade of stones used, the type of lubricant used, the number of stones on the hone head, the amount of pressure applied to the stones, the stroking rate and hone head speed in RPM.

The grit size used for efficient cutting leaves too rough of a surface for the ring materials that ECi has approved for use in a CermiNil™ process bore. Consequently, ECi production practice includes a second honing step after diamond honing which smoothes the bore surface, removes metal tears and leaves a plateau finish that ensures long ring life and minimal barrel wear during TBO. This second step is called "micro honing" by ECi but it is also known as soft honing, brush honing, whisker honing, plateau honing and ultra-finish honing. Confused? Read on…

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The basic idea behind micro honing is to use a flexible abrasive to knock off all of the garbage that is left on the surface of the bore after honing with metal bonded diamond stones. Sweeping away this debris produces a plateau-like surface that is akin to a broken-in cylinder bore. Rather than have the rings sweep away this torn and loosely attached metal, a procedure that is still widely practiced in the aviation industry, the micro honing step creates a bore surface that provides more bearing area to support the rings as they glide across the bore surface, eliminating much of the initial wear that occurs when a new set of rings are installed in a freshly honed bore.

The micro honing process is not designed to clean out grooves established by diamond honing or to de-glaze cylinder bores. By design, ECi micro honing is used to prepare the cylinder bore for immediate ring seating with little, if any, material loss from the cylinder bore on initial engine start-up. This minimizes piston and bore scuffing as well the amount of abrasion and broken cylinder wall material which works its way into the lubrication system.

CAUTION:
Don't overdo the micro honing step! Sixteen to twenty strokes are the maximum. Additional strokes beyond this can produce a finish too smooth to break in rings and too smooth to retain adequate lubrication for wear resistance, especially at the top and bottom end of ring travel. Few shops are equipped with a profilometer (a device for measuring surface roughness) so here is a slick little test that illustrates the effect of micro honing.

After finishing a CermiNil process cylinder bore with an ECi diamond honing stone, dry the cylinder bore surface. Take a cotton ball and lightly contact the cylinder bore surface rotating around 2 or 3 surface inches. Cotton strands can be seen hanging, snagged on the wall. Now use the micro hone as instructed on the reverse hereof. After drying the cylinder bore, repeat the cotton ball test and look for the difference. Very few, if any, cotton strands should be retained on the cylinder bore.

As you are reading this and recalling the relatively smooth surface on a properly diamond and micro honed CermiNil™ process cylinder bore, you are asking yourself how such a smooth surface can result in reliable ring seating. Cylinder glazing is almost synonymous with aircraft engine break in which is usually associated with excess heat and cylinder bores that are too slick to begin with. What's the trick? We've got the answer for you so read on.

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Ring Face Materials and Geometry

For steel and cast iron bores in combination with cast iron and chrome faced compression rings, the literature recommends a cylinder bore finish of Ra 28 to 35. This finish can easily be "felt" by dragging your fingernail over the surface. The old timers use to evaluate ring finish by dragging the edge of a copper penny over the surface and sensing if there was enough drag on the penny. Of course their "calibrated" fingers could also tell if there was too much drag which would mean that rings would wear out prematurely.

Surface roughness was required to grind off some of the ring face during break-in there- by "seating" the rings. This ring face profiling was facilitated on cast iron rings used in chrome cylinders by "tailoring" the ring i.e. cutting a slight taper on the ring face so that unit pressures seen by the cylinder bore surface would be significantly elevated at engine start-up. The bore roughness was also required to break-in chrome face rings used in nitrided or thru-hardened bores. The challenge, of course, was to have the bore smooth up just as the rings were broken-in, a challenge that was not consistently met due to lack of control of all of the variables.

But we haven't answered the question yet, have we, "How does a satin finish cylinder bore with a Ra of 6 to 10 reliably break in rings"?

Because of the unique properties of a nickel/silicon carbide composite coating, ECi was able to design a compression ring that incorporates a non-conventional ring face. With respect to materials, the face has a groove cut in it during manufacture and this groove is filled with plasma sprayed molybdenum. The plasma spray process produces a resultant structure that is both porous and friable. In addition to the inherent lubricity of molybdenum in the absence of oil, the porosity created on the face of the ring helps to hold oil and provide lubrication when the ring is momentarily stopped at top and bottom dead center. The friable characteristic of the ring face means that very little roughness on the cylinder bore is needed to seat the ring and in fact too much roughness will surely result in premature ring wear along with its resultant harmful effects on engine performance.

With respect to compression ring face geometry, again an unconventional design is used (at least with respect to aircraft piston engines). Instead of the ring having a tapered face (cast iron ring for chrome bores) or a flat face (chrome faced ring for steel bores), the optimum ring for a CermiNil process bore incorporates a "barrel face". The barrel geometry allows the ring to roll on the cylinder bore at top and bottom dead center rather than scrape as is the case with taper or flat faced rings. The rolling action reduces relative motion between the cylinder bore and the ring which, when aided by the lubricity of the ring coating and the extra oil contained in the pores, produces almost negligible wear on the ring and the cylinder bore. Again, a rough hone finish would destroy the barrel geometry and diminish the effectiveness of the design.

ECi CermiNil process cylinders have proven to be a very reliable product that resists both corrosion and wear. When the cylinders are rejuvenated in accordance with these procedures, fitted with ECi recommended rings and broken-in according to ECi instructions, reliable break-in and performance can be expected and achieved.