Impact of motor bearings on performance
When you have a slew of heavy, fast parts working in tandem to produce insane amounts of power, there’s going to be quite a bit of stress inside that engine. Half of the cake does everything possible to create a sufficient amount of power. The other half is ensuring that electricity is supported and produced reliably. The motor bearings are a key element in this respect.
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The job of engine bearings is to prevent unsavory metal-to-metal contact and to protect other parts and parts from wear and tear during normal engine operation. Bearings should withstand extreme abuse and work to improve the durability of the motor as a whole.
That being said, there are many considerations an engine builder must take into account when choosing the right set of engine bearings for their particular applications – fatigue resistance, reciprocating set balance, lubrication, rpm limits, heat, incorporation and corrosion resistance. – to name a few.
With performance racing applications and high horsepower engine building constantly pushing the envelope, now more than ever, new issues are arising that need to be accommodated. For example, computers and tuners now play a much bigger role in broadening engine timing curves, injection pulse and turbo boost. There’s nothing wrong with that per se, but overcharging engines and programming them to run at the rev limit for a constant amount of time can eventually cause crankshaft torsional vibration (crank flex). This then poses a problem for the bearings.
These days, a bearing (in a performance frame) has to be both hard and soft. Geometry retention is of the utmost importance, but it must also be malleable and able to adapt to stress and bending. The most important part of minimizing the risk of a slump is selecting the right bearing material.
“For modern motors, there are two basic families of bearing materials – copper-based (called tri-metals) and aluminum-based (called bi-metals),” says Mike Scott of ACL Bearing Company. “The fundamental requirement for bearing alloys is toughness. It is the ability to carry high loads balanced with soft anti-seize properties that allow the bearing to adapt and absorb harsh operating conditions.
Tri-metals are strong alloy coatings based on copper and lead with a thin layer of electrolytic babbitt. These combine high strength with the soft, forgiving properties of the coating. Adjusting the relative thicknesses of the layers and their metallurgy allows a degree of optimization so that for moderate load applications good strength can be provided with excellent anti-seizing properties providing a robust solution for standard rebuilds , especially where OE standards of engineering and cleanliness cannot be guaranteed.
For performance applications, an ultra-high-strength liner layer can be combined with a heavy-duty liner to support extreme loads with shaft-bearing interaction.
Bimetallics are medium-strength aluminum and tin-based alloy coatings, which have such full capabilities that no layering is required. However, balancing strength and anti-seize properties in a single alloy is invariably a compromise. Bimetallics that are solid tend to have significantly reduced anti-seize properties and vice versa. This makes them suitable for applications where operating conditions are moderate and predictable. In addition, these materials also have excellent durability. These reasons make them highly favored by OEMs.
Clearly, tri-metals are the benchmark for all things performance due to their increased anti-seize abilities. That being said, there is a wide range of different options that builders can choose from when it comes to selecting the correct bearings. Many of them have added overlays, a trend that has only grown in recent years.
In extreme performance applications it is basically impossible to control clearances so that there is complete separation of bearing and crankshaft. High load and high speeds mean high energy contact, which in turn causes loss of power and overheating. Bearings today are so well designed that low friction contact is durable, but coatings can further reduce friction levels and power loss.
ACL manufactures its tri-metal bearings with a 0.00025″-0.00030″ Calico coating that provides intermittent dry lubrication. CT-1 coatings reduce friction and drag and increase load capacity. Under normal conditions, performance bearing overlays withstand approximately 12,000 psi. CT-1 coated bearings increase this load capacity to 180,000 psi. Coatings are also beginning to be used on bimetallic bearings found in original stop/start motors.
“King is developing a bimetallic-coated lead-free (PL) bearing to replace many tri-metallic (CP) bearings that contain lead,” says Ron Sledge of King Engine Bearings. “This is in response to many new OE motors coming out with coated bi-metal bearings used in stop/start motors. The different types of coatings impart anti-friction properties to the surface of the bearing, thus preventing damage to the bearing during a possible loss of oil pressure.
King is also one of the few companies to offer lead-free tri-metal bearings, a recent version of their own.
“Engine bearings have to keep up with the higher loads that come with cylinder head development and big turbos,” says Sledge. “King recently launched a new silver matrix tri-metal bearing available in both uncoated (SV) and coated (GPC) variants. These materials have a 30% greater fatigue life advantage over King’s Mainstay Tri-Metal Bearings (XP, XPC). Applications will include diesel performance, racing cars and high horsepower OE engines.
While lead-free motor bearings (and other lead-free metal components) will likely soon gain traction due to environmental regulations and legislation, lead has many desirable bearing material properties. One of them being that lead is “lipophilic” – it has an affinity for certain types of oils – lowering surface tension and making the bearing surface more “wettable”.
This makes lead a good addition in high performance tri-metal bearing setups. When lead alone is not enough, the most efficient motors tend to be equipped with lead-indium bearings. A normal tri-metal bearing consists of a coating of copper, tin, lead, a bronze (copper/lead) substrate, a steel backing and a thin nickel barrier to prevent tin from chemically migrating into the substrate . When indium comes into play, bearing strength and life are affected.
“Our H bearings are made of a copper/tin/lead substrate and are 20-30% stronger,” says Dan Begle of MAHLE. “The H is a harder surface and designed to put on a lot of miles while still being stiff, so it’s good for someone who might be doing bracket racing and won’t be taking their pan off until the end of the season.
“Our v-bearings are something you might see an NHRA racer use where bearing longevity isn’t as important as they frequently remove the oil pan to inspect the bearings. These bearings are lead-indium and are considerably softer and more flexible to allow movement of the liner.When you have a lot of crank flex, this movement is very useful while maintaining its shape.
Ultimately, it’s important that motor builders consult with a bearing manufacturer before jumping into motor bearings. Although they may look like one of the simplest parts of a performance engine, taking the time to research the best possible application ensures a healthier engine and less chance of failure. BE