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XtremeOverKill
07-09-2004, 06:10 AM
HeyMC, and Everyone....

I'm considering going with Custom pistons and now I'm on to deciding on Rings. I like the thought of the Total Seals' Gapless rings...

called them up and the guy suggested an 0.035" over- Gapless second ring - I was surprised it wasn't a gapless top- with a ductile Iron Top ring -p/n = T4950-35 $240.00

Or My machinist wants to go with a set of Hastings Cast rings.

But then I start to question... If Hastings offeres a Chrome and a Moly application, WHY in the world would someone go cast.
Cast # - 693
Chrome 2C 693
Moly - 2M 693

What would you do?

jeepsr4ever
07-09-2004, 07:14 AM
Here are some articles I have read in the past




by Larry Carley, Copyright 2000 CarleySoftware.com

Stronger than ductile iron, capable of withstanding high speed pounding and loads that would destroy piston rings made of ordinary grey cast iron, and able to be formed into extremely narrow bands for bridging gaps between pistons and cylinder walls. Yes, we’re talking rings of steel. Automotive top compression rings that is.

Steel compression piston rings have been used for 30 years or more in many heavy-duty truck applications because steel is the best material for withstanding the extreme loads experienced inside high compression turbocharged and supercharged diesel engines. But steel rings didn’t make the transition to automotive applications until the auto makers started downsizing ring dimensions to reduce friction and weight. The Japanese were the first, switching to steel top compression rings about ten years ago. Ford and General Motors have followed suit, using steel in a couple of applications (the Ford 1.9L and Buick 3800 V6).

To understand why the change to steel is taking place, we need to take a closer look at the basic materials from which pistons rings are made.

IRON ALLOYS

Grey cast iron is a perfectly adequate ring material for most passenger car applications as long as the rings are of sufficient size to handle the loads. But the change to thinner low tension rings combined with efforts to squeeze more power out of smaller displacement engines has increased the operating loads on the rings, especially the top compression ring that receives the brunt of the punishment. Uncoated grey cast iron is compatible with cast iron cylinder walls and won’t gall or scuff, but it’s also brittle. Bend a ring that’s made out of grey cast iron too far and it will snap. The material has little "give" because of its microstructure. When you examine the grain structure of grey cast iron under a microscope, it has sharp rectangular grains that easily fracture if the metal is shock loaded or bent too far (a good reason for always using a ring expander when installing rings on a piston).

With narrow low tension rings (1.5 mm or 5/64 inch) grey cast iron rings can break if the engine is subjected to heavy or continuous detonation. The hammer-like blows produced by the colliding flame fronts shock loads the rings and can break them resulting in a loss of compression, cylinder damage and oil consumption problems. Though this danger can be minimized to a large extent in engines with computerized engine controls by using a knock sensor to retard spark timing, there’s no guarantee it can protect the rings under all circumstances.

Various alloys of grey cast iron are available, including "intermediate" alloys that are somewhat harder (28 to 38 HRC) and stronger. Rings made out of these alloys are used uncoated for the second compression ring in many engine applications as well as the top ring in two cycle engines. Chrome or moly coated intermediate grey cast iron rings are also used for top compression rings.

That brings us to "ductile" iron rings. Ductile iron has been used for years for heavy-duty truck gas and diesel rings because ductile iron is roughly twice as strong as grey cast iron. Ductile iron is also called "nodular" iron because its microstructure contains rounded or nodular shaped grains. These increase strength and allow the metal to bend without breaking. Consequently, ductile iron compression rings can take a lot more pounding than grey cast iron rings without breaking. In fact, you can bend a ductile iron ring like a pretzel and it won’t snap. That’s why the domestic vehicle manufacturers have been using ductile iron compression rings in many turbocharged and high output engine applications in recent years. Ductile iron has also been a popular choice for racers because of its ability to hold up in a high rpm, high stress racing environment.

But ductile iron has two drawbacks. One is that it is more expensive than grey cast iron. The basic material costs more and it is more expensive to machine. The other is that ductile iron is not as compatible with cast iron cylinder walls as grey cast iron. It tends to scuff and gall unless it is faced with chrome or moly.

Gene Hailey of Enginetech says that although ductile iron rings are definitely superior to grey cast iron, they aren’t always necessary.

"Ductile iron rings are used in all turbocharged engines and most of the engines developed since the early 1980s with 1.5 mm top compression rings to reduce the danger of ring breakage. But the higher cost of ductile iron does not always translate to better. There is absolutely no advantage to using high strength ductile iron in an engine that doesn’t require it. It’s like putting 100 octane fuel into a car with a 7.5 to 1 compression ratio.

"The one advantage ductile iron does offer is that it has a lot of bending strength and is very resistant to breaking. It is also has greater hardness, but this does not necessarily mean it is more wear resistant. Most of the abrasives that cause premature ring wear will wear a ductile iron ring just as fast as an ordinary grey cast iron ring. It’s the moly or chrome coating on the ductile ring that helps retard the wear rate."

Hailey says Enginetech uses ductile iron top compression rings in its premium ring sets for every engine application that uses ductile iron as original equipment.

How do you tell a ductile iron ring from one that’s made of grey cast iron? You can’t by appearance because both materials look the same. What’s more, both kinds of rings are factory coated with a protective black phosphate coating. So the only way to tell one from the other is to either bend a ring to see if it breaks (in which case it would be grey cast iron), or to see if it "rings." A grey cast iron ring will makes a dull thud if tapped or dropped on the floor. Ductile iron (as well as steel), however, rings like a bell.

RINGS OF STEEL

The next step up from ductile iron is steel. As we said earlier, ductile iron is roughly twice as strong as grey cast iron, and steel is roughly twice as strong as ductile iron. So steel rings can really take a pounding without failing.

Here’s how the three alloys compare:

Material Hardness Tensile Strength Fatigue strength

Grey cast iron 22-23 HRC 45,000 psi 30,500 psi

Ductile iron 38-40 HRC 180,000 psi 87,300 psi

Steel (SAE9254) 44-53 HRC 240,000 psi 138,600 psi

As you can see, steel is harder, has a higher tensile strength and higher fatigue strength that either ductile or grey cast iron. How this actually translates into ring strength and wear resistance depends on the size and shape of the rings themselves. But generally speaking, steel rings provide:

Better breakage resistance.
Improved heat resistance.
Better mechanical stress resistance.
Reduced ring side wear.
Reduced groove side wear.
Longer service life.
Jesse Jones, marketing specialist with Perfect Circle/Dana Corp., says steel rings can solve a lot of problems. They’re stronger, harder, seal better and resist breakage and wear under load. He says they’re ideal for any application that involves higher combustion temperatures, higher compression loads and tougher emission standards. "The SAE 9254 high alloy steel that we use in our rings also lower engine oil consumption. The lighter ring provides a more effective seal against the bottom of the ring groove. The smaller cross section, permitted by the greater strength, also improves the ability of the ring to conform to less-than-perfect cylinder bores. And compared to ductile or cast iron, the inherent strength of steel creates less chance of ring breakage. Steel also provides longer service life and a reduction in ring side wear and ring groove pound out."

Jones said steel has become the ring material of choice among many racers today. "Of the last 29 NASCAR races of the ‘92 season, 16 winners were running our Speed Pro steel top compression rings."

Like ductile iron, steel is not compatible with cast iron cylinder walls, so it must be coated with either chrome or moly -- or gas nitrided which we’ll describe later. The rings are made from preformed steel wire, much in the same fashion as the steel rails for oil rings. The wire comes from the steel supplier coiled like a Slinky, which is then cut to form the rings. The rings are slightly distorted (like a lock washer), however, from being coiled, so after they’re heat treated and shaped the sides must be ground flat. The steel ring is then chrome plated or face coated with plasma moly that is inserted into a recess in the face of the ring.

Most of the steel rings currently in production have a width of 1.2 mm (0.047 in.). Some are as small as 1.0 mm. Such rings are found in many late model Japanese engines (see accompanying application list). The 1.2 mm rings are about as thick as two oil ring rails stacked together, so there’s not a lot of space to machine a groove for a moly facing. That’s why the rings are usually chrome plated or gas nitrided.

The amount of machining that’s required to finish a steel ring is far less than that which is required to finish grey cast iron or ductile iron rings, so steel rings are actually less expensive to manufacture—at least in large batches. In smaller batches, however, getting steel supplier to provide the special wire that’s required can get costly—which is why the domestic ring manufacturers are taking a "wait-and-see" attitude towards expanding their coverage of steel rings for applications that do not use steel as original equipment.

Roger Borer of Muskegon Piston Rings said there’s really no advantage of going to steel in a full size ring. "Steel lends itself best to the narrow low tension ring applications because it’s too stiff for the wider rings."

Steel rings are usually barrel faced, having contoured outside diameters which gives the ring a center contact with the cylinder wall. The extremely narrow 1.0 mm rings usually have a tapered face.

Most of the ring manufacturers we interviewed said steel is unquestionably the ring material of the future, especially for the top compression ring. Like ductile iron, it is very resistant to breakage. But it’s also less expensive to manufacture.

Most of the new engines that are being introduced are going to steel. Ford’s 4.6L modular V8, which was introduced several years ago and initially used ductile iron top compression rings have been refitted with steel rings for 1993.

Though steel rings are starting to be used in newer domestic engines, most of the domestic ring manufacturers are currently using ductile iron for applications that require a premium ring material.

According to most ring manufacturers, steel and ductile iron rings can be considered virtually interchangeable as far as rebuilding most passenger car gasoline engines is concerned. So if a steel replacement ring is not available for a certain application that uses steel as original equipment, you can substitute ductile iron.

Mike Lynch of Sealed Power says, "We feel it is very important to replace these vital parts with the same high quality parts. Sealed Power has chrome plated steel replacement rings for the engine applications that require them."

Lynch also said engine rebuilders should never substitute ordinary grey cast iron rings for ductile iron or steel top compression rings because the cheaper rings won’t hold up. "Many of these newer engines are designed around the ductile or steel rings they use. If you don’t use the right type of ring, your customer is going to have ring problems 20,000 miles or so down the road."

GAS NITRIDING

Along with the change to steel rings for high output engine applications may come another new technology: gas nitriding. Gas nitriding (which should not be confused with the black phosphate coating that is currently used on most rings to prevent rust during shipping and storage) is a heat treatment process that impregnates the surface of the metal with nitrogen to case harden the metal. When used on piston rings, it case hardens the entire surface of the ring to a depth of about .001 inches which greatly improves its resistance to side wear as well as face wear. Gas nitrided rings have a hardness of about 1100 on the Vickers scale which translates into about 68 HRC which is almost 50% more than steel rings and four times that of grey cast iron rings! The rings are so hard that ring wear is virtually nonexistent. In fact, the cylinders will wear out long before the rings will.

To date, the Japanese and some of the Europeans are the only ones using gas nitriding to coat steel rings. There are no domestic production engines that yet use gas nitrided rings.

As mentioned earlier, steel rings have to be coated so they won’t scuff, so gas nitriding may someday replace chrome plating as the coating of choice for tomorrow’s steel rings.

Roger Borer of Muskegon said domestic manufacturers are looking at the gas nitriding technology but are currently invested in chrome plating. "The future of gas nitriding rings depends on what kind of environmental restrictions the EPA puts on chrome plating. I’d guess that within the next 5 to 10 years, gas nitriding will replace chrome plating. The question then becomes is it more economical to do the gas nitriding in house (as we do chrome plating now) or do we farm it out to an outside vender.

Ring manufacturers have also been tinkering with various combinations of plasma moly and ceramics (such as chromium carbide). Ceramics are extremely hard and wear resistant, but do not conduct heat well. So the amount of ceramic in the mix has to be limited to match the application. Ceramic faced rings have been developed for drag racing applications, and Volvo currently is using a "Moly Cermet" (80% moly/20% chromium carbide ceramic) faced ring in a turbocharged heavy-duty truck engine. But for everyday passenger car applications, gas nitriding appears to have the best chance of being universally accepted.





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by Larry Carley, Technical Editor
lcarley@babcox.com

Though piston rings haven’t changed much in recent years, they are still just as important as ever for sealing compression, reducing blowby and emissions and controlling oil consumption. The changes that have occurred in ring designs, materials and cylinder bore refinishing techniques have been more evolutionary than revolutionary. Subtle refinements over the years in rings and cylinder bore refinishing techniques have created a generation of engines that can easily go 150,000 miles or more in most passenger car and light truck applications, and up to a million miles in big heavy-duty diesel trucks before a ring job is needed.

Better ring sealing and longer lasting engines are a bonus for vehicle owners. But for aftermarket ring suppliers and engine rebuilders, it’s been a curse. Fewer traditional engines are being rebuilt today than a decade ago. The bright spot has been performance engine building and other niche markets ranging from subcompact diesels to restorations. The performance market continues to show steady growth year after year in spite of a sluggish economy. Racers and hobbyists are spending money on engines for their racecars and restorations, but not necessarily their daily drivers.

Less traditional engine repair volume means more competition for the engines that are being rebuilt. Consequently, some engine rebuilders are substituting less expensive plain cast iron rings for moly rings and chrome rings to improve their profit margin and/or competitiveness. Likewise, some ring suppliers have felt compelled to add cast iron ring sets for engines that were not originally equipped with these type of rings because their competitors have them and the market is demanding them.

Tod Richards of Dana/Clevite Engine Parts says Dana has been adding new cast iron ring sets to its product line this year to cover applications that never had these kind of rings. "Cast iron ring sets are what many of our customers want," says Richards. Richards notes that the decision to use cast iron rings by some engine builders is being driven by price competition in today’s market."

Cast iron rings obviously won’t last as long as moly faced rings in hard-working late model engine applications, but how long they last often depends more on the quality of the engine build than the type of ring that’s used. Richards says cast iron rings will work well but only if the cylinders are properly cleaned after honing. This means scrubbing the bores with hot soapy water to remove all the honing residue and abrasives from the surface of the metal.

Aftermarket ring manufacturers are also having to add more new ring sets for newer applications, too. "Like other ring manufacturers, we have to follow the OEM lead and keep up with changing ring sizes. That means more new ring sets as rings continue to shrink in size," says Richards.

Rings are also running hotter than ever before. As rings move up higher and higher on the piston to reduce emissions, they are seeing more and more heat. The top ring on many engines today run at close to 600¬? F, while the second ring is seeing temperatures of 300¬? F or less. Ordinary cast iron compression rings that work fine in a stock 350 Chevy V8 can‚Äôt take this kind of heat. So that‚Äôs another reason why many top rings are now steel or ductile iron rather than cast iron.

More Changes Coming?
Scott Gabrielson of Federal-Mogul/Sealed Power says things seemed to have "settled down" for awhile as far as new ring designs and materials are concerned with the domestic engine manufacturers. "Passenger car and light truck engines built for the North American market are mostly using moly faced 1.2 mm top rings, 1.5 mm second rings and 3.0 mm three-piece oil rings. We’re seeing more steel top rings but the second compression rings are still mostly cast iron with a reverse-twist taper face. It’s a combination that is working well so there’s no pressing need to change things – for now."

There are some exceptions. The current Buick 3800 V6 uses a narrow 2.0 mm oil ring. Gabrielson also says some second rings now have a "napier" style face. The napier design has a small notch in the bottom face of the ring to improve oil control and sealing as the ring scrapes against the cylinder wall. The napier design is also used with a positive twist to improve its sealing characteristics.

Though ring designs appear to be stable here for the moment, such is not the case in Japan and Europe. The Japanese are continuing to shrink ring sizes with some late model engines now using 1.0 mm and smaller top compression rings. The Japanese don’t use moly facings but prefer gas nitrided rings for added longevity. North American ring manufacturers say nitriding is too expensive and moly works better because it is porous, holds oil and is more scuff resistant. Even so, nitriding remains popular in Japan.

Jack Bishop of NPR America (Nippon Piston Rings) says the Japanese want to push fuel economy to the max. Their current goal, he says, is to build engines that get 100 kilometers to the gallon (that’s about 62 mpg, which is light years beyond the current U.S. CAFE requirements of 27 mpg for passenger cars). One way they hope to achieve their goal is to reduce internal engine friction by shrinking ring dimensions even more. The Honda Civic that’s currently being sold in the Japanese market has tiny 0.8 mm top compression rings.

"The Japanese are also working on variable tension rings that change tension as engine load and temperature change. Variable tension rings reduce friction when the engine is cold, then stiffen up at higher loads and rpms to maintain a good seal.

"The Japanese are also looking at titanium nitride surface treatments for new production rings. Right now, titanium nitride rings are available for high-end racing engines but they are expensive. However, the rings are super hard and experience almost zero wear. The goal, says Bishop, "is to get manufacturing costs down so they can be used in production engines within the next two or three years."

The Europeans, by comparison, use a mix of ring facings: moly, chrome and nitride. Like the Japanese and domestic OEMs, they, too, are using smaller and smaller rings. But much of the ring development work that’s going on in Europe today is now aimed at small diesel engines. The Europeans are buying more diesel-powered cars than gasoline-powered cars because of the diesel’s higher fuel economy. They don’t have the same emission regulations as we do, so diesels are a popular engine there.

Diesel engines run leaner and hotter than gasoline engines, so hard, durable ring facings are needed to provide good longevity. Moly works well in diesels, but engineers are also working on developing new composite facings that combine ceramics, moly and other ingredients.

One of the big changes that will impact the longevity of diesel rings in the years ahead are new emission regulations that require exhaust gas recirculation (EGR) on heavy-duty trucks. Some engineers say diesel engines that were capable of going a million miles before EGR will be lucky to go half that distance because of the higher combustion temperatures – which is good news for diesel engine rebuilders. Time will tell if such predictions hold true.

Performance Ring Sets
Performance engine builders are always pushing the envelope and are the most demanding of all ring customers. They want rings that can withstand extreme abuse while also providing the best possible seal. Reducing blowby increases horsepower so a tight seal is absolutely critical to winning races.

A lot of the cutting edge ring and piston technology that’s being used in racing today will eventually find its way into production engines. The piston and ring sets that are found in many production engines today were considered racing parts less than a decade ago, so it’s logical to assume such things as "gapless" rings and exotic coatings may be in OEM engines before long.

Keith Jones of Total Seal Piston Rings says eliminating the end gaps in the compression rings can improve horsepower by as much as 10 percent depending on the application. "Our gapless rings have been very popular with racers, but we also have conventional rings, too, and offer both types with various coatings."

"We have steel rings down to 0.6 mm size in both gapless and conventional designs. Our ‘Diamond Finish’ rings are manufactured to within 50 millionths of an inch flatness and parallelism, with a finish that is typically 4 Ra microinches or less. This allows tighter assembly tolerances for better performance."

Jones says Total Seal’s most popular face coating material is "C23," which has a coefficient of friction of 0.1 (three times better than moly) and won’t flake off like plasma moly. It also works well with hard blocks and nickel silicon carbide-lined cylinders. Total Seal also offers a "C72" titanium coating, "C33" chrome nitride coating and conventional moly coatings as well, plus a "D47" side coating for the top and bottom of its steel Diamond Finished rings to reduce groove friction and microwelding.

"We’re the Burger King of piston rings. We’ll do rings anyway a customer wants them," says Jones.

The key to choosing a particular ring design and coating, says Jones, is to identify an engine’s primary function in life. If an engine is a street/strip application, chances are it will spend 90 percent of its time on the street. For this kind of engine, street rings would work better than an all-out racing ring. Of course, it all depends on the compression ratio and whether the engine has a blower, turbo and/or nitrous oxide (in which case racing rings would be better).

"If you don’t know which type of rings to use, call us and we’ll help you figure it out," says Jones.


Vern Schumann of Schumann’s Sales & Service, Blue Grass, IA, says ring selection for performance engines depends on three things: compression ratio, the type of fuel (gasoline or alcohol), and horsepower. Schumann says plain cast iron rings should never be used in an engine that burns alcohol because alcohol cuts lubricity. Coated rings are a must with alcohol.

Gas nitrided steel rings manufactured from coil wire are best for turbocharged and blown engines, says Schumann, and especially those that run nitrous oxide for an extra power boost. He says nitriding penetrates into the surface of the metal and alters its chemical makeup. Because of this it can handle thermal shock much better than any add-on facing material and won’t flake off under load.

"One of the biggest misconceptions that’s out there is that moly faced steel rings are racing rings. Welded moly steel rings work great on the street but won’t hold up like nitrided steel top rings," says Schumann. "Nitrided rings are stronger, provide better heat transfer, and won’t flake from thermal shock. In five years, I think most racing engines as well as many street performance engines will be running nitrided rings instead of moly."

Schumann explains that the different coil steel wire used in rings provides different tensile strengths. "The coil steel wire we use in our rings has a tensile strength of over 200,000 psi with zero porosity. Other alloys commonly used to make moly rings are typically 50,000 to 55,000 psi. Ductile iron, which we recommend for the second ring if the compression ratio is over 11 to 1 or the engine makes more than 400 hp, is rated at 70,000 to 80,000 psi. But ductile is typically two to eight percent porous, which reduces heat transfer and cooling. Ductile iron must be used with a coating, otherwise it smears the cylinder walls."

Schumann says the biggest mistake any engine builder can make is to use cheap rings with racing pistons. The rings should be steel or ductile iron so they don’t fail. Otherwise they are likely to break, and when that happens you can kiss the piston and the motor goodbye.

Cylinder Bore Refinishing
As a rule, engine builders should follow the cylinder bore refinishing guidelines by the ring manufacturer. But like every other aspect of engine building, opinions differ as to what techniques work best in any given situation.

Federal-Mogul’s Gabrielson says a "plateau finish" is the optimum bore finish for today’s moly-faced rings. A plateau bore finish is what all types of rings eventually produce when they are fully seated, so the closer the bore can be prefinished to a plateau-like condition the less the rings and cylinders will wear as the engine breaks in, the better the rings will seal right from the start, and the longer the rings will last.

For moly rings, Gabrielson recommends a two-step honing process: first hone with a conventional #280 grit silicon carbide vitrified abrasive, then finish by briefly touching the bores with a #400 grit stone or giving them several strokes with an abrasive nylon honing tool or brush.

If the cylinders are honed with diamond, Gabrielson says to follow up with finer grit diamond, a fine-grit vitrified abrasive or a brush to finish the bores. Diamond stones are fast and long lived, but they are more aggressive than silicon carbide and create more tear outs and other undesirable residue on the surface. Because of this, a rough diamond honing procedure should always be followed up with another operation afterwards to finish the surface.

Equally important is bore geometry. Gabrielson says engine builders have to be especially careful about oil control on late model engines. He says the block should always be honed with torque plates if the manufacturer recommends doing so to minimize bore distortion that can cause blowby and prevent the rings from sealing properly.

"The bores have to be straight and round. Make sure you keep the Ra finishes within factory specifications, too, which is typically in the 10 to 15 Ra range on many late model engines."

Jeff Welsh with Peterson Machine Tool says #220 grit silicon carbide honing stones are the best choice for plain cast iron and chrome rings, #280 grit is best for moly-faced rings, and #320 to #400 grit is best for moly rings in a racing application. To finish the bores, Welsh recommends using a brush hone or flexible brush in a drill.

"The main advantage of finishing the bores with a flexible brush in a drill is that you can run the drill backwards. The honing stones usually run clockwise so if you brush in the opposite direction (counterclockwise) it will do a much better job of deburring the surface. No more than 15 strokes should be necessary to produce a high quality finish."

Welsh also says crosshatch is important. Some people want 30 degrees and others as much as 45 degrees. "Thirty is probably best. We now offer an inverter with our honing cabinet so the operator can vary the spindle speed as well as stroking speed to achieve as much crosshatch as he wants."

Michael Mohondro of Rottler Manufacturing says most ring manufacturers call for a bore surface finish of 10 to 20 Ra microinches (see sidebar on page 35). "If the bores are honed with #325 to #400 diamond stones, the finish will usually be in the 22 to 24 Ra range. If the bores are then finished with a brush, they usually come down to about 18 Ra which is just about right."

Mohondro says some OEMs are using a much coarser grit of diamond to increase valley depth in the bores for better oil retention and ring break-in. He says International Harvester is using #140 to #170 diamond stones to hone their cylinders, then finishing with #600 stones to plateau the surface. This leaves a surface finish of 10 to 14 Ra but with 60 to 100 Ra of valley depth to retain oil.

"Most racers are also using #600 diamond stones to plateau the cylinders after they have been honed to get a really smooth finish," says Mohondro.

Tim Meara of Sunnen Products Co., says there are a variety of ways to achieve a plateau finish. You can use conventional abrasives, cork bond stones, a plateau honing tool or a two-step diamond honing process.

"Sometimes the cycle time dictates the type of process or stone that’s used. If an engine builder wants a fast cycle time, he may use a coarser grit stone to rough hone, then follow up with a finer stone to plateau finish the bore.

"Typically, most production engine rebuilders are using #320 or #400 grit diamond stones today, followed by brushing using a #180 grit PHT tool."

Meara says Sunnen has recently introduced a new honing head for its CK21 that holds both diamond stones and brushes in the same tool. This allows a user to hone with diamond. The diamond stones then retract and the brushes extend to finish the cylinder without having to change anything.

One change Meara says he’s seen lately among some race engine builders is a desire to increase the "Rvk" numbers (valley depth) in the crosshatch to improve oil retention.

Another issue is how to minimize bore distortion when the engine is running. Torque plates have long been used to simulate the bore distortion that occurs when the cylinder heads are installed on the block. Honing the block with torque plates installed results in rounder holes and better ring sealing. But temperature is also a factor that’s hard to duplicate.

Mart Jeltema of K-Line says the type of plateau finishing procedure he recommends depends on the engine and type of honing equipment an engine builder is using. "What kind of honing machine are they using or are they honing with a drill? What Ra finish are they trying to achieve, and what kind of finish are they getting before they attempt to plateau the cylinders?" he asks

To achieve a plateau finish, Jeltema recommends using a brush: either the rigid style that mounts in the honing head holders or a spaghetti style bristle brush in a hand-hone (K-Line sells both types). He says it usually takes about 10 to 15 strokes in each cylinder to plateau the finish. The improvement is generally about 10 Ra points on the surface finish.

Ed Kiebler, a consultant for Winona Van Norman says he still recommends a 15 to 20 Ra finish for moly rings. Anything less than 12 Ra can result in glazed cylinders and the rings may not seat.

"You can use various methods to get there. Winona Van Norman still uses conventional vitrified abrasives. A #280 grit stone will give you the right finish, but it should be followed with a plateau honing tool that loads into the hone head – not a bottle style brush. The soft honing tool does not exert enough pressure against the surface to change the overall Ra finish but it will do an excellent job of removing all the torn and folded metal you don’t want on the surface. It makes a huge difference in ring seating and oil consumption."

Kiebler says diamonds can produce good results, too, provided they are used in a hone head with at least eight stones and are followed up with a brush for 20 to 30 seconds. A set of #400 grit diamond stones will produce a finish that is similar to #280 vitrified carbide stones.


Analyzing Cylinder Bore Finishes

(from a presentation by Michael Mohondro, Rottler Manufacturing)

For many years, cylinder bore finish has been analyzed by using the roughness average (Ra) parameter as a primary means. This measurement is very effective in determining the "smoothness" of a cylinder wall after it has been finish honed, although it is not enough to fully determine if a cylinder has been finished properly. Monitoring the cylinder finish is very important for many reasons, with the importance being to find such a method that makes rings seat faster and last longer.

One method that can be used to analyze bore finish is fax film. Fax film analysis provides a qualitative determination of torn and folded metal, burnishing, pull outs, and hone crosshatch.

A more detailed method of analysis are the Rk parameters of measurement. The Rk parameters directly analyze the bearing characteristics of a cylinder over a given sampling length. These measurements are graphically illustrated on the Abbott-Firestone Bearing Curve. This type of analysis also provides a qualitative determination of torn and folded metal, burnishing, pull outs, and hone cross hatch angle.

The Ra parameter can have many different forms, while still maintaining the same value. This is simply because Ra is only an average. The same Ra number can represent three very different surface finishes though each has the same average roughness. This being the case, it becomes very important to look at additional parameters when analyzing the surface finish. These include the Rk value, the Rpk and Rpk values, and the Rvk and Rvk values.

The Rk value refers to the bearing area that exists after the rings have seated. Rk is the height of the cylinder wall profile after the highest peaks and lowest valleys have been removed.

Rpk monitors how much material must be removed from the cylinder wall before the rings have seated, providing a good seal (reducing effects such as blow-by). Inconsistent high peaks (Rpk) are filtered out of this equation, and are not as important because they immediately are "knocked off" upon starting the engine.

Rvk refers to the valleys in the cylinder bore finish, filtering out the lowest extremes. This is a very important characteristic, indicating the surface’s oil retention qualities. Typically, a high Rvk value is very acceptable and indicates that the cylinder bore is effective in holding oil across its surface.

The plateau level is commonly described by the ratio of Rk to Rvk. This is a direct comparison of the bearing surface roughness to the valley depths.




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CermiNil® Process vs. Nitrided Steel

The CermiNil® process is both, an OEM process and a repair process. As an OEM process, it is used in new products by many of the world's leading engine manufacturers like Ford, Mercedes, Suzuki, Porsche and others. ECi incorporates the CermiNil process as an option in its line of new Classic Cast cylinders. As a repair, the CermiNil process offers the advantage of restoring the cylinder bore dimensionally allowing the salvage of worn or rusted bores. Either as an OEM or as a repair process, the CermiNil process results in a cylinder bore that is far better than a nitrided bore. The most obvious advantage is in corrosion protection. The natural corrosion resistance of nickel differs greatly from nitrided steel's affinity to corrosion. Additionally, the CermiNil process provides a surface which is uniform throughout as opposed to nitrided steel which is a case-hardened surface that varies in hardness along its depth and can show soft spots. These soft spots lead to uneven and premature wear.

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Ring Finish and Break-in

Break-in of a CermiNil process cylinder is unique and cannot be compared to any other cylinder bore/ring combination. The smooth surface of the CermiNil process bores produces reliable ring break-in, which is especially significant when installing new rings during cylinder mid-life. A normally run CermiNil process cylinder bore surface without any surface roughening will accomplish ring break-in equally as well as a new cylinder. Run-in procedures are specified in the ECi handbook entitled "Break-in Instructions".

Environmental Considerations

ECi GOES GREEN! Laboratory research has shown that the chromium chemical used in the chromium plating process is a carcinogen. While the resultant metal coating poses no hazard while it is in the engine, disposing of waste from the plating process as well as disposing of the grinding debris from the cylinder overhaul process is becoming more difficult and costly. The cost of disposing of chromium waste is expected to rise dramatically in the future. By contrast, waste management costs associated with the CermiNil process are affordable now and are expected to stay at present levels well into the future, thereby insulating the customer from pass-through disposal costs.

Wear Rate vs. Coating Cross Section

CermiNil process excepted, all cylinder bore surface treatments currently approved for use in aircraft piston engines have the common characteristic of exhibiting increasing wear rates as the bore enlarges due to the effects of friction. As the chart indicates, the beneficial features present on the surface of a new cylinder bore begin to diminish as the cross sectional thickness is reduced. Lubrication is reduced during periods of high cylinder temperature as well as high power settings. Therefore, once lubrication between piston ring and cylinder bore deteriorates and friction begins removing metal from the bore, wear rates will irreversibly begin to climb, resulting in an extreme ring step.

The CermiNil process, on the other hand, has a uniform composition throughout its entire cross section, meaning that any short-term increase in wear rate due to reduced lubrication is temporary and wear rate will return to normal when lubrication normalizes.

Chrome vs. Nickel

Chrome and nickel have many similarities but also one important difference. The two metals are similar in the sense that they can be plated on steel with excellent adhesion. The use of chromium for building up worn cylinder barrels has a long and successful history. Both nickel and chromium are very corrosion resistant and can be removed and replated multiple times. An important difference is that nickel is oil wettable and chromium is not.

More Repairable Cylinders

It is not uncommon for used cylinders to have barrels that can not be saved by grinding oversize or by plating back to standard. Excessive corrosion and wear as well as physical damage to the cylinder barrel make some cylinders non-repairable. The historical fix for this condition is to rebarrel with a new forging which may not be cost effective. The proprietary technology incorporated into the CermiNil process includes a certificated method which permits most cylinder barrels and heads to be selectively fitted to mating parts other than the originals. Therefore, a barrel with a non-repairable defect can be discarded and replaced by a used or new barrel. This valuable service can be provided for a small additional cost.

Identification of the CermiNil Process

The coating produced by the CermiNil process can be identified by its color, texture, by performing the copper sulfate test on it or by the silver color painted on the flange of the cylinder. With regard to color of the coating, nickel usually has a yellow tinge when it is finished to a low Ra. However, alloy steel can also have a yellow tinge when highly finished. Polished chrome, on the other hand has a bluish tinge. The copper sulfate test is the most reliable method of differentiating the CermiNil process from a steel bore. Copper sulfate solution applied to a steel cylinder bore will turn the steel to a copper color (nitrided steel reacts slowly, so be patient). Copper sulfate applied either to a chrome bore or a CermiNil process bore produce no change in color. The texture (surface finish) of the CermiNil process is smooth by comparison to a traditional ring finish for steel. Except for loss of cross hatch, there is very little difference in appearance between a new CermiNil process cylinder bore and a cylinder bore with several hundred hours of operating history. Externally, the area of the cylinder which normally receives a color code to indicate the type of cylinder bore material, will be painted with two (2) silver bands. A teal color painted between the bands indicates that the head has been treated with the IFR process.

Head and Barrel Interface

The CermiNil process cannot be performed on a cylinder barrel which is assembled on an aluminum head. Therefore, all cylinders will be non-destructively disassembled before processing by using an FAA approved proprietary process which has many years of successful field experience.

A major benefit resulting from disassembly is the ability to inspect all hidden surfaces including the threads on both the aluminum head and the steel barrel. This procedure fully meets the requirements of FAR 43.2. Using dye penetrant inspection on the aluminum threads and magnetic particle inspection on the steel barrel allows ECi to make a higher level of airworthiness assessment on a used cylinder than anyone else in the industry.

Piston Rings for CermiNil Process Cylinder Bores

The CermiNil process has been FAA approved to operate with a molybdenum faced top compression ring and flake-graphite cast iron rings in the remaining positions. This combination provides optimum results with reliable break-in and increased durability.

The ring sets for CermiNil process bores are designated as "CN" ring sets and are sold exclusively by ECi. To order CN ring sets contact ECi Customer Service at 1-800-ECi-2FLY (800-324-2359) or e-mail us at: sales-service@eci2fly.com.



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What's the difference between "Chrome Plating", "Chromium Plating", "Chrome Dipping", "Chroming", etc.?

Nothing really. Chromium is a metallic element, and chrome is just a slang name for it. Things are not made of solid chrome. Rather, they are made of something else (often steel or plastic) and electroplated with a coating of chrome. Chrome is always applied by electroplating, it is never melted onto parts in the fashion of chocolate on strawberries.

An additional cause of occasional confusion, however, is the fact that people may tend to describe any shiny finish as "chrome" even when it really has nothing to do with chromium. For example, highly polished stainless steel parts, nickel plated parts, parts painted with a highly reflective aluminum paint, and parts coated with vacuum metallized aluminum may be referred to as "chromed" by people who are not familiar with the subject.



So all chrome plating is about the same, then?

No. There are two different general applications for chrome plating: "hard chrome plating " (sometimes called "engineering chrome plating") and "decorative chrome plating" (sometimes called "nickel-chrome plating").



Hard Chrome Plating

Most lay people would not be familiar with hard chrome plating. Hard chromium plating is simply chrome plating applied as a fairly heavy coating (usually measured in thousandths of an inch) for wear resistance, lubricity, oil retention, and other 'wear' purposes. Some examples would be hydraulic cylinder rods, rollers, piston rings, mold surfaces, thread guides, etc. It is called hard chromium because it is thick enough that when a hardness measurement is performed the chrome hardness can actually be measured. It is almost always applied to items that are made of steel. It is metallic in appearance but is not really shiny or decorative.

There are variations even within hard chrome plating, with some of the coatings optimized to be especially porous for oil retention, etc.

Many shops who do hard chromium plating do no other kind of plating at all, because their business is designed to serve only engineered, wear-type, needs.

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