Bearings play a pivotal role in piston engines, ensuring that the force applied to the crankshaft by the connecting rods is efficiently converted into rotation rather than potentially dislodging the crankshaft due to frictional forces.
Considering the multitude of engine designs as well as the use cases for them, it’s no surprise there’s a wide range of engine bearing options out there to choose from, and as development techniques and manufacturing processes evolve, so do the offerings available to builders.
Here we’re going to take a closer look at the latest updates in bearing technology and get some expert tips from the folks at Clevite and King Engine Bearings on how to make the right bearing selection for a given application.
Like any internal engine component, accuracy and consistency in manufacturing process of engine bearings is essential to both the performance of the parts they support and the longevity of those components.
A unique feature to all King coatings is there is no added thickness to the bearing wall – our STD coated bearing is the same thickness as an STD uncoated bearing. – Ron Sledge, King Engine Bearings
And when it comes to bearing construction, Clevite offers a unique development of their own. “Our performance engine bearings are a trimetal design consisting of a steel back; a cast, copper-lead intermediate layer and a Babbitt or Lead Indium overlay,” explains Clevite’s Bill McKnight. “We are the only company with a cast intermediate layer, everyone else uses a sintered process. The dendritic structure of the cast copper-lead provides superior load carrying capacity to a sintered material.”
McKnight tells us that the lead indium overlay, often known as Vandervell design, is also exclusive to Clevite. “Since it is a bit softer and more forgiving, it’s a popular option in NASCAR as well as blown alcohol and blown nitro motors.”
The coating of an engine bearing is an important factor to consider when making a selection, particularly in applications that are purpose-built for the upper echelons of high performance and motorsport use. Coatings guard against seizure, enhance wear resistance and protect the bearing surface from oil starvation. Choosing the right coating for a given application ensures that the bearing performs with maximum efficiency.
I’m a strong believer in coated bearings for performance applications, but this is ultimately a personal preference. – Bill McKnight, Clevite
The three coatings currently offered are all geared toward the specific needs of different applications. “pMaxKote is specially made for use over soft substrates like on top of pMaxBlack overlays found in XP bearings,” Sledge tells us. “It is designed to enhance lubrication when oil films are at a minimum.” pMaxKote is also designed to protect bearings during metal-on-metal contact, as well as from the erosive effects of cavitation.
The second coating King offers is specially made for use over hard substrates like bronze or aluminum. The coating is harder and will withstand higher loading than pMaxKote, making it ideal for very high horsepower applications that range from approximately 2,500 to 5,000 hp.
The third coating King offers is a soft sacrificial type of coating that is applied over hard substrates like bronze and aluminum. “It’s formulated to abrade and work in applications where direct friction contact occurs, like in Top Fuel drag racing,” Sledge says.
Clevite provides their own approach when it comes to coatings, too. “Our aftermarket performance coatings are based upon PTFE (Polytetrafluoroethylene), moly and graphite in a blend,” says McKnight.
“We also offer a very tough, durable coating used to great success in the blown alcohol and nitro motors. Additionally, we provide advanced coatings at the OE level based upon PAI (Polyamide-imide) rather than PTFE in which wear extenders are added to the PAI to get OE life expectancy.” Clevite says that a performance bearing which offers this coating should be available by the fall of 2017.
In terms of the break-in method for coated bearings, while there’s nothing especially unique about the procedure, “A little bearing lube during assembly and a good break-in oil is a good idea if a break-in is done,” says McKnight. “But many of our customers go pretty much to full-power racing almost immediately.”
OK, we’ve got a lot of options when it comes to coatings, but what about the base materials used for bearing construction? “Steel is the substrate for most engine bearings, be they trimetal designs or bimetal aluminum designs,” says McKnight.
“It’s also possible to make a solid aluminum bearing but you do not see them in engines very often,” he adds.
However, that doesn’t mean that aluminum is a rarely used material in bearing construction, as King’s latest offering uses a bi-metal construction that is comprised largely of aluminum. “The newest base material that we have introduced is our SM material,” says Sledge.
“This is an aluminum based bi-metal alloy containing manganese and chrome for added strength and fatigue resistance.” Designed for high-load applications while providing solid levels of wear resistance, King’s material guide lists SM as their strongest aluminum-based offering.
Lug vs Lugless Designs
Those familiar with engine bearing design know that the lug on a bearing is there strictly to locate it fore-aft in the housing bore. “Since the lug pockets in connecting rods and blocks need to be machined, OEM have been eliminating lugs for bearings for some time now,” McKnight points out.
“Back about 10-12 years ago we developed an ‘indentless lug’ design for NASCAR. It provided a smooth ID at the parting line and reduced the tendency of the bearing to fracture at the lug indentation on the very narrow bearings used in NASCAR. However, we didn’t see a need for it outside of this application, as our customers continue to prefer and use the traditional lugged bearings that we’ve offered for years.”
When it comes to OEM applications, Sledge’s thoughts on the subject echo McKnight’s. “The OEMs have started using connecting rods and bearings without lug slots and lugs on bearings,” says Sledge. “This is mostly for economic reasons because these days the bearings are machine loaded at the factory so there is no need to have a locating lug. Since the locating lugs have no effect on bearing retention, then the lugs can be eliminated.”
However, this is a challenge for the aftermarket, since bearings are installed by hand. King recently developed the “Smart Lug” which means the lug is present on the OD steel back side but there is no depression on the corresponding ID side. “A benefit of this design is that it helps eliminate oil leak paths,” Sledge explains. The Smart Lug is designed with the locating lug protruding from the back of the bearing without removing any material from the surface side of the bearing.
Choose The Right Bearing For An Application
With the number of different factors to consider when selecting an engine bearing for a specific build, devising a strategy can be a helpful way to figure out exactly what you need. “Engine load and duration capacity requirements are fundamental factors,” says Sledge.
“Builders also need to consider the engine’s use and rebuild cycle, along with the crankshaft material used in the application.” Wear resistance, embedability and conformability are bearing attributes that need to be considered as well.
But beyond bearing attributes, there are some factors that should be taken into account right out of the gate. “Before doing anything, see what is available from your bearing supplier,” says McKnight. “If you have the luxury of starting from scratch, pick a very common bearing like the CB1798 NASCAR rod bearing or a small-block Chevy bearing – this provides advantages like multiple choices in size, coatings and material design, and a good likelihood of it being around in 10 years. I’m a strong believer in coated bearings for performance applications, but this is a personal preference,” he adds.
It’s clear that there’s a few different schools of thought when it comes to both bearing design and how to hone in on exactly what would work best for a particular build. “Develop a relationship with your bearing company of choice,” says McKnight. “They’ve got experience and usually very good knowledge of what works and lots of experience helping you when things are not working so well,” he aptly points out.