BEARING MATERIALS

At the original equipment level, the use of aluminum main and rod bearings is growing for a variety of reasons. One is that aluminum bearings are less expensive to manufacturer than bimetal or trimetal copper/lead bearings. Switching to aluminum also gets rid of lead, which is an environmental concern for manufacturers. But there are many other reasons, too.

"Federal-Mogul provides both copper/lead and aluminum bearings. But perceptions are changing with respect to aluminum versus copper/lead," said Federal-Mogul's Ron Thompson. "Most of the original equipment manufacturers are going to aluminum bearings, as are a growing number of rebuilders in the aftermarket. Many people are switching to aluminum because it provides improved durability and better control over tolerances.

"Overplated bearings tend to trap and hold dirt that can score the crankshaft. But aluminum bearings tend to flush out debris rather than hold it. Aluminum bearing alloys also contain silicone which helps resist seizure and actually polishes the crank.

"I can see the day when traditional copper/lead bearings may only be used for racing," said Thompson.

Ed Pavelick at King Engine Bearings, Cedar Grove, NJ, says that 95 percent of his company's aftermarket bearings are now aluminum. "We made the decision to go to aluminum several years ago when we developed our exclusive Alecular bearing material. Itis an aluminum alloy that contains tin, copper and several other elements. We think it provides the kind of longevity that today's market demands."

Pavelick said that traditional trimetal rod and main bearings have a three-layer construction. The steel backing plate is covered with a layer of copper/lead overlayed with a thin (.0005 to .0008 in.) coating of babbitt. King�s aluminum alloy bearings, by comparison, use just two layers, a .012 to .015 inch thick layer of their Alecular alloy over the steel shell. Pavelick says this provides greater conformability as well as better embedability for microparticles larger than .0004 inch in diameter, which are most responsible for scoring cranks and tearing or weakening thin babbitt overlays.

Another plus with aluminum, says Pavelick, is that it has greater temperature resistance than copper/lead. The melting point of their aluminum alloy is over 1,100 degrees F, which is almost three times as high as babbitt. This provides added protection against localized overheating due to detonation, overloading, misalignment and similar conditions.

Bob Anderson, engine bearing team leader at AE Clevite Engine Parts, Ann Arbor, MI says that although many OEMs are using aluminum, trimetal copper/lead bearings are still the preferred bearing material for the aftermarket.

"We have stayed with a traditional trimetal copper/lead bearing because thatis what the aftermarket wants. We believe trimetal copper/lead offers the best combination of strength, surface action and embedability. Copper/lead can carry 12,000 pounds per square inch versus about 7,000 to 8,000 psi for aluminum, it can handle less than perfect conditions, and is a more forgiving material than aluminum in a typical aftermarket application.

Chris Worthington, a bearing engineer at ACL Automotive America Inc., Tucker, GA said that although the Japanese are using a lot of aluminum bearings, Ford and General Motors are still using copper/lead bearings in many of their engines because of the high strength of the material. As for the aftermarket, most of it remains copper/lead for domestic engines and a mix of copper/lead and aluminum bearings for import applications. He said the high performance market is almost all copper/lead bearings.

"Although most rebuilders still prefer copper/lead because it is a more forgiving material, others prefer to use the same bearing material as the original bearings. So we have both aluminum and copper/lead bearings" said Worthington.

Gene Hailey, vice president of technical services at Enginetech, Inc., Carrolton, TX, said his company is looking at aluminum bearings but for now is sticking with copper/lead because that is what everybody wants.

"Our main concerns with aluminum are its load carrying ability and embedability. Oil filters typically only screen out particles that are about seven microns and larger in size, so the bearing material must be able to handle the dirt that gets through."

As for the environmental issues associated with lead, it is mostly a concern for bearing manufacturers not end users. "The government is not concerned about the amount of lead in used engine oil because the amount is usually insignificant."

One change that Hailey said has been made in Enginetech bearings is to reduce the amount of eccentricity and crush relief. Although greater eccentricity increases oil flow to improve bearing cooling and longevity, it also causes a slight drop in oil pressure readings on engine test equipment used by many large rebuilders. So to produce more traditional test results, eccentricity was reduced.