We’ve all seen engine bearings and probably have taken them for granted. These little half shell, simple pieces of metal look so common and inexpensive that they couldn’t possibly be that intricate and instrumental in engine operation. Actually, looks can be deceiving and the simplicity of engine bearings hides the sophistication of decades of research and development invested into these essential engine components.

We wanted to get our intellectual bearing on the technology behind engine bearings by talking with leading experts in the field. Along the way we discovered how to choose the bearings for different engine applications and considerations for sizing bearings for different engine combinations. If you think you know everything there is to know about engine bearings, we challenge you to read on. For a component that is inexpensive when compared to other engine components, the engineering technology behind bearing manufacturing is surprising.

Our Experts

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MAHLE Clevite's Bill McKnight and King Engine Bearing's Dmitri Kopeliovich

 

 

We listened to two highly respected authorities in the field, Dr. Dmitri Kopeliovich, Research and Development Manager of King Engine Bearings and Bill McKnight, Team Leader of Training at MAHLE Clevite, as they educated us on bearing technology. Between Kopeliovich and McKnight, there is over a half century of experience in engine bearing technology. Needless to say, these guys have seen it all.

 

What does an engine bearing do?

According to our experts, engine bearings do more than take up space between the engine block housing and the rotating shaft that it supports. King Engine Bearing’s Dr. Kopeliovich explained the basic functions of the bearings include; “Protecting the housing and shaft from damage and wear with surface qualities that can withstand the harsh engine operating environment.”

McKnight added “The design of engine bearings allow for a layer of oil to form between the rotating shaft and the surface of the bearing so that the shaft does not actually ride on the bearing itself but on a formation of an oil wedge that supports the rotating shaft under normal operation.” By riding on a layer of oil instead of the bearing itself, “the bearing helps dissipate heat,” McKnight said.

Kopeliovich further explained that the bearing face is designed so that; “particles in the oil  are allowed to embed into the bearing to protect the rotating shaft from being damaged.”

Based on what our experts said, engine bearings protect rotating shafts like camshafts and crankshafts by supporting a layer of lubrication, dissipation of heat and keeping small particles from damaging the shaft’s polished journal surfaces.

 

How do engine bearings perform those tasks?

Simply looking at the bearing shell does not tell the whole engineering design story. For example McKnight detailed a couple of design features that are not easily detectable by casual observation;“The split bearing shells are not eccentric or uniform in wall thickness. Each half of a split bearing is made so that it is slightly greater than an exact half. These things are done by design to aid in the formation of the oil wedge and keep the bearing from spinning in the housing.”

McKnight went on to explain why the split bearing halves are slightly larger than an exact half; “ This extension is called crush height. When the split bearings are snapped into place in the housing, as the bolts are tightened the bearings compress like springs. The resulting force holds the bearings tight and prevents them from spinning in the housing bore.”

Through talking with our experts we discovered the crush height designed for each application is critical for the primary functions of the bearings. McKnight clarified by saying, “the crush height sets up radial pressure on the bearing halves so that they are forced tightly into the housing bore. By forcing the bearing into the housing bore the bearing back is snug against the housing bore surface area to support the bearings and help transfer heat away from the bearing.”

Types of Engine bearings

Dr. Kopeliovich outlined the different types of engine bearings, “bearings may be mono-metal, or solid type bearings, a bi-metal, tri-metal or multi-layered. Most engine bearings are either bi-metal or tri-metal.”  McKnight explained that “most of our everyday bearings, other than the late model stuff, is still tri-metal, which is steel-backed, with a cast copper lead intermediate layer and then a babbitt overlay.”

The type of metal used in construction also plays a critical role in aiding the design features mentioned above and still play a significant role in the other functions of engine bearings. The real challenge is making a bearing that is strong enough to support a crankshaft or camshaft spinning thousands of revolutions per minute, yet soft enough to allow particles to embed into the bearing to protect the shaft’s journal surface.

Dr. Kopeliovich agrees that it’s a tough challenge but using a composite of materials can achieve the goal of making a bearing that has soft metal and hard metal characteristics. According to Kopeliovich there are different types of composite manufacturing. Particulate structure, Lamellar structure and a combined Particulate-Lamellar structure.

• A particulate structure consists of a strong matrix with soft particulate distributed throughout to provide the strength and softness combination.
• A lamellar structure is composed of layers of different materials. In this case, engine bearings use a steel back layer with one or two layers of softer metal.
• The combined Particulate-Lamellar structure couples the two methods together.

Kopeliovich explained the popular Lamellar stucture as being two distinct types; “By using a steel back overlaid with different metals you can provide softness and hardness at the same time and they are broken down into two basic families of these types of bearings, bi-metal which has one layer over the steel and tri-metal which has two layers over the steel backing.”

So if you’ve been paying attention, there’s a lot more to an engine bearing than we originally thought. Let’s summarize what we’ve learned so far:

• Engine bearings are designed with an eccentric wall for greater oil flow to flush out particles and carry heat away.
• Each bearing half is made larger than an exact half for a crush zone that helps the bearing fit snugly against the housing.
• Most bearings are manufactured with layers to provide strength to support the crankshaft, connecting rod or camshaft, yet soft enough to allow embedding of particles.
• Most engine bearings are either a two or three layered lamellar structure.

Materials for every application and regulation

Almost every bearing manufacturer would agree that there is not one engine bearing that covers every type of automotive application. Remember, an engine bearing’s primary function is to support the load of the rotating shaft.

To give you an idea of the wide range of loading that crankshafts can be exposed to, McKnight expressed the load potential by cylinder pressure; ”A normal passenger car can have cylinder pressures around 1,200 psi range. An 800-900 horsepower race engine may have cylinder pressure in the 2,200 psi range. A 2,000-3,000 horsepower race engine will have pressures in the 6,000 psi range and a 7,000 horsepower top fuel engine will likely be in the 10,000 psi range.”

It’s clear that a bearing that would operate in a standard passenger car won’t fair as well in a 7,000 horsepower engine. In addition to being able to handle the load created by engine performance, bearings must also be manufactured to handle the increasing legislative demands of the global markets. The Europe Union (EU) has issued a directive to remove lead from automotive engine, transmission, and compressor bearings by July of 2011 (heavy duty applications are exempt) and Asia has started to move toward the lead free engine component trend.

With all the environmental regulations that are under revision world wide, material selection, along with research and development have taken on a wider role in the manufacturing of engine components. Not that any of this is unexpectedly new, both King Engine Bearings and MAHLE Clevite have a wide portfolio of lead free engine bearings for various applications.

“We have had a complete portfolio of lead free aluminum bi-metal materials for bearings, bushings, and washers in production for years. We also have lead free bronze bi-metal bushings and washers and tri-metal bearing offerings in the early stages of roll out and validation at OEM customers,” said McKnight.

Current Materials

Dr. Kopeliovich outlined some of the materials that have been used in different engine bearing applications, “Steel, copper, aluminum, silicon, lead, tin and nickel are used. These can include particles of ceramics and particles of solid lubricants in the composite materials. Along with selection of the materials, adhesion between the layers is not a simple process but is very important.”

Breaking down the material properties into five functions, Kopeliovich explained how different materials are selected based on application:

1. Load carrying capacity: A material that can withstand indefinite max cycle loading.
2. Wear resistance: A material that can retain it’s dimension. Both Load carrying capacity and wear resistance require a stronger material. The stronger the material, the better the characteristic will be.
3. Compatibility: The material must be compatible with the shaft to prevent adhesive wear or seizure.
4. Embedibility: The material must be able to absorb small particles. This requires a softer material.
5. Conformability: Requires a material that can accommodate minor misalignments and irregularities.

According to Kopeliovich, “Most of the time steel is chosen for the backing material for support and a strong contact with the bearing housing. This is overlaid with softer materials that gives makes a strong bearing with soft characteristics on the top layer.”

McKnight says, “most bearing manufacturers use a similar grade of steel for the backing of tri-metal engine bearings. SAE 1008 and SAE 1010 are the most common ones used.”

Years of history and analytical data have went into making these materials the industry standard. McKnight confirmed that MAHLE Clevite has an ongoing research and development program that continuously explores all current technology and materials looking for any advantages in engine bearing manufacturing.

Conventional Wisdom

Dr. Kopeliovich has explained that many of today’s engine bearings “are manufactured by either casting or sintering technology.” In either case, Kopeliovich says “adhesion between the layers is very important.”

According to McKnight, Clevite’s method of manufacturing bearings is “cast the intermediate layer onto the steel in a strip process where an alloy of molten copper and lead is poured onto the steel strip in an atmospheric controlled furnace. Copper in the alloy penetrates the steel forming an indestructible bond. As the strip leaves the furnace, it is quenched and the alloy solidifies.”

King utilizes a process of manufacturing called sintering. Kopeliovich, a prolific writer on engine bearing technology told us, “Properly sintered material has no pores and voids. It is as strong as a properly cast alloy. Additionally, sintered material may be strengthened (if required) by cold rolling and/or varying its chemical composition.”

Engine bearings and oil. How they co-exist.

Regardless of what material the bearing is made of, the lifespan of a bearing in a street or race engine would be about as short as a Mayfly’s without lubrication. The process of reducing wear in moving surfaces in close proximity that allows a smooth continuous operation is a science all to itself.

Lubrication is one of the key factors that affects bearing operation. What makes bearing lubrication unique is that the motion of the contacting surfaces, and the design of the bearing, pumps the lubrication around the bearing creating a layer of lubricating film that  supports the rotating shaft. According to Dr. Kopelivoich, “This is called Hydrodynamic Lubrication and it works best for bearings when the oil film thickness is larger than the surface roughness.”

There are several factors that can cause lubrication changes and the hydrodynamic lubrication regime can turn into a boundary film lubrication regime where metal to metal contact can occur during load cycling. McKnight explains that, “oil starvation, high loads, low rpm speed, roughness of bearing or shaft surfaces can affect bearing lubrication. Because the bearing is designed to create an oil wedge by the shaft’s rotation, when the engine is not rotating, there is no substantial bearing lubrication. During start up, there will be a minor amount of solid to solid contact until the film is built up around the bearing.”

Kopeliovich says, “constant cycle loading is what causes fatigue in the bearing, which is the main cause of bearing failures. If he load was always constant, there would be no fatigue.”

 

What Bearings Tell Us

By now we are getting the idea that there is much more to these consumable engine components. We’ve also detected that manufacturers of engine bearings do not like to use the term “bearing failure” going with a more acceptable “bearing distress” phrasing. Understanding that a bearing does not fail unless it experiences a distress for another reason is important to fixing an engine problem. Our research into bearings has explained the engineering that goes into the component, the materials that are selected in the making of these products and what purpose a bearing actually serves.

Stay tuned for Part 2 where we find out how to diagnose bearing “distress”, probable causes of premature wear and how to properly install engine bearings, including checking for oil clearances. We also be addressing the different coatings that are available for engine bearings, and the controversy that surrounds whether to coat or not.