Dialing in on Today’s Engine Bearing Trends
When selecting engine bearings, engine builders often focus on getting the proper clearances and maintaining sufficient oil pressure, but other bearing characteristics should also be considered in certain applications.
By Brendan Baker
Durability is less of a concern today because the aftermarket and OEMs demand bearings that can last 150,000 miles even under severe stress from a neglectful vehicle owner. In performance applications there are a number of materials that will do the job well. Each material has its advantages in terms of resistance to corrosion, rate of wear, embedability and fatigue strength.
In light duty passenger car engines aluminum bimetal has been the bearing material of choice for several years. Although each manufacturer has a different compound mix of aluminum and some type of silicon the bearing is made of, bimetal aluminum bearings have proven to last virtually forever in light duty, low to medium load engines.
MAHLE Clevite’s Bill McKnight says the company is going to introduce a whole new line of aluminum bearings for the production engine remanufacturer (PER) market later this year due to demand. “PERs seem to have the most demand for aluminum bearings,” says McKnight.
“That’s where we get most of those requests. But most of our everyday bearings, other than the late model stuff, is still trimetal, which is steel-backed, with a cast copper lead intermediate layer and then a babbitt overlay.”
While trimetal copper lead bearings are available for a wide range of applications, including performance applications, bimetal aluminum is used almost exclusively in today’s light duty passenger car engines. And a more recent trend has seen a move to a lead-free bimetal bearing for environmental reasons.
“When you talk about trends, especially in the aftermarket, we’re really looking at lead-free bearing materials,” says Federal-Mogul’s Matt Barkhaus
. “In a big way, we’ve been pushing our A-Series bearings for the last several years and it’s been an evolutionary product. Today, we have a material called A-590 which is totally lead-free. It’s a very strong bearing, almost equal to our basic trimetal bearing (H24). So that’s the big deal for us right now.”
The real push for lead-free components is coming from Europe, say experts, where the use of lead in new engine designs is being restricted beginning in 2008. So OEMs in the U.S., with hopes and plans to export products to Europe, are designing all of their new engines and transmissions to meet the new directive which has to do with the recyclability of engines and engine parts after they have been scrapped.
Generally, bearing manufacturers say the strategy has been to get away from the lead because of the various environmental issues and to stay competitive with global markets. And some believe it’s just a matter of time before these initiatives come to the U.S.
Currently, there isn’t any legislation on the horizon in the U.S. to restrict the use of lead, however, experts say Europe is setting the tone and most of Asia is following suit; all of Asia’s new engine bearing designs are also lead-free.
Michael Flynn of ACL, an Australian- based bearing manufacturer that operates in the U.S., says his company’s aluminum bearings were developed for their Japanese OE customers, and one of the things that was really critical for them was it had to be lead-free.
Flynn says it’s not a regulation in Japan that the bearings have to be lead free, and the amount of lead in the ones that do contain it is very nominal, but ACL’s aluminum bearings were developed initially for OEs.
“We knew that everyone would use this lead-free bearing. It’s similar to how MLS gaskets have taken over the late model passenger car engine market. They all use it,” says Flynn.
“The domestic passenger car market in the U.S. is practically all bimetal aluminum,” says Federal-Mogul’s Raymond King. “There are some bearings that have lead in them still but we’ve converted almost all of our A-500 applications over to A-590, so some of the older engines that have been out a while with A-500 are now converted to A-590. The amount of lead in that bearing was pretty nominal at about two percent anyway, but I believe after this model year there won’t be any A-500 left: it’ll all be A-590 from us.”
Says King, “We think we’re better off going the lead-free direction and being on the front end of the curve.”
“In a stock production engine, where everything is straight and round, that aluminum bearing will last virtually forever with little signs of wear,” acknowledges MAHLE Clevite’s McKnight. “You can tear the engine down with 150,000 miles on it and the bearings still look like new. Another advantage is that it doesn’t cost as much for aluminum bearings as the trimetal. So for a lot of these reasons we’ve decided to add a line of aluminum bearings this year. We get a number of rebuilders who request them.”
The material makeup of a good bimetal bearing features good sliding properties with very high fatigue strength, says Federal-Mogul’s King. Combing these characteristics in just the right formula is where bearing manufacturers say they have all their attention focused these days. Bearing experts say it’s difficult to come up with a good combination of slipperiness and strength because they’re conflicting properties.
“You need hard, strong materials for fatigue strength and at the same time you need soft material for sliding properties, embedability and conformability characteristics,” says King. While King says the company’s A-590 material does a pretty good job of doing this other formulations are being tweaked to meet expectations.
Not to be left out of the stock replacement discussion are trimetal bearings. While OEs may be moving away from trimetal copper lead bearings for stock applications they are still available for many engine applications in the aftermarket and remain a viable choice for engine builders, particularly in engines that may have been poorly maintained, thanks to trimetal bearings reputation as forgiving of irregularities in surface conditions.
“Trimetal bearings cover probably 85 to 90 percent of our bearing applications. The spots where you find our bi-metal aluminum bearings in the standard line is in late model import and a few domestic engines,” says McKnight.
“The tri-metal bearing is substantially stronger than a bimetal aluminum bearing, by around 30 percent and it’s more forgiving of crankshafts that aren’t perfectly round, smooth and straight,” says McKnight. “Bimetal aluminum works really well if everything is perfectly smooth and true. That’s why the OEs use it with such success because they have the capability to produce the required surface conditions with very precise equipment. But if you have any grooves, ridges or irregularities on a crankshaft then a babbitt overlay that can compensate for that and align itself can be a better choice.”
The major engine bearing manufacturers offer a full line of performance bearings to meet specific engine and component requirements. Some bearings are narrower, for example, so that you can fit them on a crank with a large radius. Others feature super soft materials for extreme embedablity, but at the expense of durability. The majority of performance bearings are trimetal that are modified for higher load applications.
While the standard Chevy rod bearing and a race bearing should have the same clearance, McKnight acknowledges that if you checked 100 of them you should find more uniformity in the race bearings, because they try to keep the tolerance a little tighter. On race bearings, especially on those for the rods, McKnight says MAHLE Clevite offers a bearing called “Xs,” which offer .001" extra clearance. He says it’s also permissible to combine Xs, standard bearings and .001" unders also, allowing builders to mix and match bearings within .001" of each other. They can get costly , however, because you have to buy extra sets to come up with the combination you need.
MAHLE Clevite will introduce a cryogenically treated rod bearing later this year for the Top Fuel class.
“We’ve developed and run them with a couple of teams. They’ll hit the market as soon as we can get them on the shelves,” says McKnight.
Federal-Mogul’s Speed Pro line is the company’s super-duty alloy tri-metal H-14 bearing. “All the global brands have their individual design features but they use basically the same tri-metal material in their performance bearings,” says F-M’s Barkus. “Other bearings may have an enlarged chamfer or some other feature but we actually have a specific tri-metal material for our performance line, which can withstand 15,000 psi of load.”
King Engine Bearings currently offers a performance silicon aluminum bearing for many high horsepower applications. “It’s machined a little differently and there are some dimensions that are changed to increase crush. In addition, the oil holes are opened up a little to improve oiling and eccentricity is a little different,” says King’s Ed Pavelick.
Pavelick says King’s bearings are also chamfered for radius on the crank so there is some narrowing of the bearings. But the material is basically the same material as King’s other Alecular bearings.
Pavelick say King sells performance aluminum bearing for just about everything except NASCAR.
“Our bearings DO cover about 90 percent of the performance market,” says Pavelick. “There are certain applications where we may not recommend it but we cover most everything. In terms of psi we’re probably in the 10,000-11,000 psi rang. Above that, you may start to have trouble in higher horsepower engines. So that is one reason why we don’t use our bearing in NASCAR.”
Pavelick says some of the Top Fuel and drag race applications are also too much load for the Alecular bearings, and marine as well. “We don’t pursue the marine market because they are typically a severe duty application where the engine is run wide open for long periods of time at high rpm and high loads. But there are some people who do use our bearings successfully in these applications.
According to Pavelick, King is planning to launch a new performance bearing in the near future that will be able to handle any type of race engine in the market. He says they are developing a high-end material for this bearing that will be a trimetal bearing. They’ve already done testing on it and are going into production, so Pavelick hopes to launch it soon.
Pavelick says one of the advantages an aluminum bimetal bearing offers to performance engines is that, even when the bearing starts to fail the crank doesn’t get damaged and you get a warning because you can see it in the oil. Normally when a trimetal bearing fails the crank is also ruined. A lot of racers like it for that reason because they can just swap out the bearings and they don’t have to replace the crank, he explains.
ACL Bearings’ Flynn says that ACL covers domestic and imports bearings but its strength is in its import bearing coverage, particularly in the racing market, where it has a broad line of trimetal import race series bearings.
Several bearing manufacturers offer bearing sizes of .001" under or over, and a .009" under or .011" over, for doing some select fitting in performance applications. However, for stock replacement applications, it’s pretty much the usual .010s, .020s, and .030s for most applications, according to experts.
“We do offer quite a range of sizes,” says King Engine Bearings’ Pavelick. “On the performance side we offer a lot of select sizes mostly around .019s and .021s but we don’t do any around the .030s. We do some actual .030s but no .029s or .031s. We also offer a standard .001 and a standard X, which is one below standard. And we offer both sides of the .010s, and .009 and .011. The standard X is for the standard crank that needs more clearance.”
He continues: “Even though relatively few engine builders will need them, we go up to .050 or .060 in a few applications. On the imports we generally stop at .040s. And on the domestic side there’s not that much demand for the .060s anymore so some manufacturers have discontinued it. It’s not typical to go to these sizes; most bearings only go to the .030s.
Engine Pro’s Ron McKey says that its “crank saver” bearing in many different sizes can help prolong crank life.
“The best example would be the first time the crank is serviced, and since many people have a high-dollar racing crank, we make the bearing in a .009" and .011",” McKey explains. “So instead of turning the crank to .010" and then the next time going to .020" or something larger, you can save it by turning to .009". Then the following season if nothing catastrophic happens you can polish it and use the .010" or maybe even .011". What it really does is extend the life of the crank providing there are no catastrophic failures.”
Engine builders are used to select fitting bearings to adjust to a range of journal sizes but McKey says this is a way to get more life out of the crank, and they’ve found that many people aren’t comfortable going to .020" on a racing engine.
“I think a lot of people just turn the crank first and then go look for bearings. We try to tell people to check it and see if you can go to .009" or .011" if you’ve already gone to .010". It can give your crankshaft a new lease on life, which is important considering the investment.” says McKey.
NASCAR is generally split 50/50 with teams that use the coated bearings and teams that don’t. Some swear by the coating and others don’t see the value in it and run it how it is out of the box, says one expert. It’s still a big issue for a lot of performance engine builders, and two major bearing manufacturers offer their own line of coated performance bearings but experts say they’re sold generally to enthusiasts and DIYers. However, Calico Coatings sells mainly to the NASCAR teams and others at that level. Calico and other coating companies buy their bearings from major manufacturers and then add their coating.
Although coating companies have had an excellent following for a number of years, coatings are relatively new for the bearing manufacturers themselves and most only offer it for select performance applications. MAHLE Clevite is in the process of adding more coverage because it’s been popular. Experts say it’s cheap insurance.
Federal-Mogul says its coating consists of a moly tungsten disulfide in a resin base. It’s a solid film lubricant which has that property of absorbing and holding the oil, which prevents metal-to-metal contact from a dry start.
Federal-Mogul’s Barkus says the decision was made to do the coating in house to control it more at the manufacturing level. “You can do some damage if the coating isn’t applied properly,” he says.
For the most part, experts we spoke with are in one of two camps when it comes to coatings: those who use them and like the results and those who don’t see any benefit.
Some bearings feature a groove into the lower bearing called a 3/4 groove, which keeps oil pumping up to the rod bearing for a longer period of time. It helps keep the rod bearing lubricated. This groove gives full load carrying capacity in high stress areas in the lower end. It’s the best of both worlds, say experts: good oil flow to the rod bearing and in the highest loaded area you have more surface to handle it.
The grooves, whether half-groove or full-groove, depends on each specific application but it’s primarily the performance applications in which you’ll find the 3/4 grooves.
On the Horizon
For the future, some bearing manufacturers are looking at product enhancements they can do after the bearing has been manufactured to make it better.
MAHLE Clevite’s McKnight says cryogenic treatments to bearings are one of the options they’re looking into. McKnight says if the process gives 3 or 4 percent more strength it could make a difference.
Another process he says they are looking at is a micro-peening process that will compact the surface and make the molecules a little denser and also stronger. This is a popular option in the sport compact market right now so some manufacturers are looking at adding this process as well.
“Some engine builders may look at it as kind of gimmicky but others swear by it. And if you’re out at the edge, 3 or 4 percent is a big deal,” says McKnight.
Most experts say engine builders are beginning to look at bearings differently because the modern race engine makes a lot more power than in the past. Engine Pro’s McKey says he knows of racers who are making upwards of 2,000 hp with his bearings. So it’s a critical issue because a lot of these applications are supercharged or nitro or turbocharged. And forced induction is really putting a strain on engine components.
Racers tend to get carried away with that kind of power and they can keep wicking the engines up until something breaks. Because it’s a pretty expensive failure when that happens, bearings and everything else in the engine is becoming more critical to understand. Manufacturers are doing their part to help the engine builder.