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Getting Your Bearings

Engine bearing suppliers talk about materials, selection and more

By Brendan Baker

Page 1 of 2

Engine bearings have a tough job to do for such a small component. They must support big loads on a thin film of oil (between .0001-.0004˝ thick) between themselves and the crankshaft journals to prevent metal-to-metal contact.

One of the biggest causes of bearing failures is dirt and debris that enters into the oil pan and gets sucked between the bearing surface and the crankshaft, interrupting that thin film of oil, creating a metal-on-metal contact. From that moment, various engine applications and bearing materials may react differently but the end result is usually still the same – a wiped bearing. And no engine builder or bearing manufacturer wants that.

We spoke to bearing manufacturers to find out what direction technology is heading regarding bearing materials and design, as well as how engine builders can better understand which bearings to use in specific applications.

“As engines have developed, ‘design’ and ‘manufacturing’ have become increasingly important terms,” says Mike Scott of ACL Bearings. “This is predominantly driven by the increase in engine efficiencies resulting in higher bearing loads and higher bearing operating temperatures while utilizing lower viscosity lube oils.”

The result, according to Scott, has been generally decreasing oil film thicknesses between journal and bearing. “As minimum oil film thicknesses can be less than .0004˝, the shape (design) and manufacturing precision are key to assisting the generation of stable oil films and ensuring shaft-to-bearing separation under all operating conditions,” he explains.

Although quality bearings have inherent properties that compensate for a degree of misalignment (what bearing engineers refer to as conformability) and provide protection from hard contaminants within the oil (embeddability), engine builders can do a lot to ensure bearing durability by paying close attention to crankshaft preparation and overall cleanliness of the build. In fact, a significant percentage of bearing failures can be traced back directly to the assembly process, so it is a good idea to keep it as clean as possible.

“What is most important for installers is cleanliness in the assembly,” says Federal Mogul’s Bob Sturk. “Everything must be as spotless as possible. Dirt is the number one killer of bearings. When we have failures it’s always, by a vast majority, from debris and embedded dirt.”

Echoing Sturk’s cleanliness comments, MAHLE Clevite’s Brett Dayringer says that thoroughly cleaning the block after machining is the best way to prevent dirt and debris getting into the oil system after a rebuild.

“Using hot soapy water and a good selection of bristle brushes is the best method for cleaning cylinder blocks, crankshafts and other engine parts before reassembling the engine,” says Dayringer. “Remember, any debris remaining after a rebuild will be picked up by the oil system and make its way to the bearings.”

Another important consideration when working with your engine bearings to pay attention to is that the wall sizes are consistent so that you can set the clearances without having to go through and measure several bearings for the right fit.

From a manufacturer's perspective, King’s Ron Sledge says they recognize that bearing sizes and application-matched materials are very important to the installer and end user. “The installer wants very consistent bearing wall sizes to easily zero in on his desired clearance,” says Sledge. “His cranks are supplied with a consistent size, so he wants the bearings to measure consistently also. He can also save time and money not having to measure different bearing shells to get the correct one to achieve his clearance.”

ACL’s Scott says that his company’s solution, similar to King’s, has been to enhance their precision in the manufacturing process. “We have a portfolio of bearing materials with proven robustness across the range of engine applications,” he says.

Scott continues, “This provides the engine builder with the basic confidence of operating capability. The enhanced precision, particularly over bearing wall thickness, provides additional confidence that optimized bearing clearances will be achieved resulting in: optimized high pressure oil film generation for better load support; increased durability; more predictable oil pressure and flow rates to ensure constant supply throughout the engine; and adequate bearing cooling under all operating conditions.”

Materials Matter
The selection of the right bearing material is vital to a trouble free performance with any application. The most commonly used materials in crankshaft bearings are aluminum, copper, lead and tin. Obviously there are others, say experts, but these are the primary elements that are used. And they are all, on a comparative basis, much softer than the iron and steel crankshafts that run against them.

“Bearing materials are called on to satisfy many different conditions in the engine including load, embeddability and seizure resistance, just to name a few obstacles that they must overcome,” says Sledge.

Luckily, say manufacturers, years of research and testing have developed different material solutions for everything from street duty use to ultra high performance to optimize bearing performance in the aftermarket.

As most engine builders know, modern engines (late ’90s and newer) use bi-metal aluminum bearings, but each manufacturer has its own recipe for the construction and characteristics they are looking for. The basic construction is a steel back with a layer of silicone-aluminum facing the crankshaft.

If you are doing a stock rebuild, Federal-Mogul’s Matt Barkhaus says that it is very simple to choose the right bearing from the catalog, which will list all the specs and various sizes available.