The importance of the engine’s bearings can’t be over-emphasized. The bearings support the crankshaft and connecting rods, and in pushrod engines also the camshaft. The bearings provide a surface for the friction-reducing oil film that allows the parts to spin without rubbing metal against metal. It’s a tough job because of the high loads created by the forces of combustion and the reciprocating mass of the pistons.
Over time, the constant pounding takes a toll on the rod and main bearings. Metal fatigue can form cracks that eventually lead to flaking, spalling and bearing failure. Dirty oil can score and damage bearings, and loss of oil pressure almost guarantees certain death. A dry bearing is soon a dead (or seized) bearing. Acids in the crankcase can also attack and pit the bearing surfaces.
As bearings wear, oil clearances increase causing a loss of oil pressure. Rod bearings may also become noisy, producing a rhythmic rap, rap, rap that beats in sync with engine speed. The potential here is to also cause computer problems with the knock sensor as well. Any of these symptoms are reason enough to replace a set of bearings.
With high performance engines, the bearings are subjected to even higher loads and rpms. This requires a stronger bearing material and close oil clearances to maintain peak oil film strength thickness.
Almost all late model passenger car and light truck engines in domestic and Asian vehicles are now equipped with aluminum rod and main bearings as original equipment. European vehicle manufacturers still use a lot of copper/lead bearings because they have a high percentage of diesel engines (where cast/copper/lead bearings are preferred because of their load carrying capacity) and consequently, and typically cast their bearings. By comparison, most U.S. bearing manufacturers typically use a sintering process to manufacture their bearings, although there is one U.S. manufacturer with a full line of cast/copper/lead bearings.
The domestic and Asian OEMs have gone to aluminum bearings for several reasons. One is that aluminum alloys contain little or no lead. This reduces the potential for environmental lead pollution when used motor oil is recycled.
An “A-500” aluminum alloy, which has been used in many engine bearings since 1994 and is the most commonly used alloy today, contains 8 percent tin, 3 percent silicon and only 2 percent lead. The next generation “A-590” alloy, which will be used by most North American OEMs in the coming years, contains no lead whatsoever. The A-590 alloy is a harder, more durable alloy with twice as much silicon (6 percent) and half the tin (4 percent) and also contains no lead. The A-590 alloy will be used in high output passenger car engines as well as heavy-duty diesel engines.
The OEMs also like aluminum because of the low cost and the fact that aluminum is a hard material that withstands wear better than copper/lead bearings – provided the oil is kept clean. After 150,000 miles, aluminum bearings in a properly maintained engine typically show minimal wear.
Unfortunately, aluminum has little embedability. Consequently, any hard abrasive particles that find their way between the bearing and journal may become trapped and score the surface. With a softer copper/lead bearing, solid particles become embedded in the bearing surface where they are less likely to cause scoring.
One way aluminum bearing manufacturers address the embedability issue is to bore the inside diameter of the bearings when the bearings are made rather than to broach them. The boring procedure leaves tiny “micro-grooves” in the surface that help flush out contaminants while improving oil retention, seizure resistance and fatigue resistance.
Aluminum also has a higher temperature rating than copper/lead. The melting point of a typical aluminum bearing alloy is over 1,100° 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.
As great a bearing material as aluminum is, it may not be the best choice for every application – particularly for engines that may not be remanufactured to like-new tolerances under the cleanest conditions or for engines that do not see regular oil changes. Because copper/lead bearings are softer, they can typically handle more irregularity in journal surfaces. Copper/lead bearings also provide good embedability, so if dirt or wear particles find their way into the oil it reduces the risk of scoring a journal surface.
Copper/lead bearings are still the number one choice for racing applications. Although aluminum is harder, it doesn’t have the fatigue resistance to loading that copper/lead can provide. Even for a tough aluminum alloy such as A-600, the recommended limit is 100 hp per liter. So for a 500-plus hp V8, a copper/lead performance bearing would be needed to handle the load.
A typical trimetal copper/lead engine bearing has a three-layer construction. The steel backing plate is covered with a layer of copper/lead overlaid with a thin (.0005? to .0008?) coating of babbitt. The bearing may also have a thin flash plating of tin for cosmetic purposes. The three-layer construction provides a good combination of strength, surface action and embedability. Cast/Copper/lead can carry in excess of 14,000 pounds per square inch of load versus about 7,000 to 8,000 psi for an aluminum bearing, and can better resist wiping and scoring under heavy loading say those who make these kind of bearings.
Aluminum Vs. Copper/Lead
The ongoing debate of aluminum versus copper/lead bearings is nothing new, and will likely continue for the foreseeable future, said Hunter Betts of Enginetech Inc., Carrollton, TX. “As far as we’re concerned, there is only one way to go, and that’s with our 780 bearing material. It is a sintered trimetal bearing with a base alloy of copper, lead and tin with a nickel dam and babbit top layer.
“We don’t really care what the OEMs are using because they are building new engines in a clean environment. Our customers are production engine rebuilders who need a material that will hold up in their kind of environment.
“Our 780 alloy has a higher load carrying capacity than aluminum or other commonly used copper/lead alloys. It costs more to manufacture, but we think it is worth it because of its improved durability, conformability and embedability.”
Betts said detonation can sometimes be a problem that leads to premature bearing failure. Often times, an engine rebuilder has no control over how an engine is installed or other conditions that may affect engine operation. So using a premium bearing with a higher load carrying capacity provided added insurance against detonation failure.
A different opinion was voiced by Ed Pavelick of King Engine Bearings, Cedar Grove, NJ. “Our Alecular Si aluminum alloy bearing material outperforms traditional trimetal bearings and provides superb results.” Pavelick said King bearings have a single deep (.012? to .015?) layer of Alecular alloy comprised of aluminum, tin, copper, silicon and other metals over a steel backing. This provides both high fatigue strength and wear resistance. The bimetal bearings are unplated and bored so abrasive particles flush through the bearing rather than stick and score the crankshaft. The unplated surface also allows for closer control of wall thickness (plus or minus .0001?), which allows for precise tolerances and a precision fit. Pavelick also said his Alecular bearings perform well in racing applications, not just stock and light duty engines.
Tim Vehlewald at ACL Bearings, Grand Rapids, MI, explains that his company has introduced a new line of “Aluglide 810” aluminum bearings made of aluminum, silicon and tin. ACL is also makes copper/lead standard and performance bearings. The new line broadens their market coverage and offers customers a broader choice of replacement bearings.
Matt Stites, Clevite 77 bearing product manager says: “As the industry changes, so must we as a supplier. Our philosophy is to provide the best replacement bearing for the application. It may be tri-metal cast/copper/lead/, bimetal-Aluminum or micro-babbit”.
Bob McBroom of Dura-Bond, Carson City NV, says cam bearing materials are still pretty much the same. “Babbit is a very forgiving material and works best in aftermarket applications. Some of the OEMs are going to aluminum cam bearings, but they can bore semi-finished bearings to achieve perfect bore geometry.”
McBroom said Dura-Bond is also offering teflon-coated cam bearings for performance applications. “We have coated bearings for all the aftermarket blocks (including Dart, Brodix and World) plus Chevy and Ford V8s. The teflon coating adds an extra degree of protection. We can also custom make oversized cam bearings for engine builders who are blueprinting the cam bores.”
The latest news in performance bearings is the availability of coated performance bearings from two of the leading bearing manufacturers: Dana/Clevite and Federal Mogul/Speed Pro. Both companies unveiled their new coated bearings at the recent Performance Racing Industry Show in Indianapolis.
Though coated performance bearings have been available for many years from such companies as Swain Coatings, Calico Coatings, Polydyne and others, the entry of Clevite and Speed Pro into this realm has brought coating technology into the main stream.
Various types of coatings have been used to reduce friction, improve wear resistance and heat management. But the primary purpose of today’s bearing coatings is to protect the bearings against dry starts and damage if oil pressure is lost. In other words, it adds an extra layer of protection should the oil film go away.
Barry Rabotnek of Federal Mogul said the “Duroshield” Competition Series coated bearings feature a unique molybdenum disulfide (MoS2) coating in a polymer base that is applied over an H-14 alloy copper/lead bearing. Coated main and rod bearings are currently available for small block and big block Chevy, small block Ford, and for Honda rod journals.
“We will be adding more coverage as we go forward with this new product line,” said Rabotnek.
The coating, which is only .0003? thick, has a “hydrophilic” matrix which bonds to the bearing surface and absorbs oil to improve lubricity and reduce friction. Rabotnek said the new bearing line has been tested and proven under brutal operating conditions, including running in a 3,000 hp twin-turbo drag engine at nearly 240 mph, and a record-setting Camaro at the Bonneville salt flats.
Don Sitter of Dana Corporation said Clevite’s new “TriArmor” high performance coated bearings use a proprietary moly/graphite coating in a PTFE polymer base to reduce friction and provide extra insurance against oil starvation and abuse.
“In a perfect world, you don’t need a coated bearing. But in the real world, a coating provides an extra measure of forgiveness and protection. So we now have coated bearings for those who want this kind of protection and are willing to pay for a premium product.”
The TriArmor coating, which is only .0003? thick, is applied over a standard Clevite 77 H-Series or V-Series bearing. There are no other modifications to the bearings and the bearings can be installed with the same fit as before.
Sitter said the standard rule of thumb for bearing fit is to allow .001? of oil clearance per inch of journal diameter, plus an additional .0005? fudge factor. But with the coated bearings, you don’t need the additional fudge factor. In fact, the coating provides additional conformability.
Sitter cautions against using bearings with coated parting lines because bearing crush is vital to a proper fit and bearing longevity. For this reason, the parting lines on Clevite’s Triarmor bearings are not coated. “In a racing engine, a .0003? coating on the parting line can increase the total crush effect by .0012? (.0003? x 4). Initially, this causes the bore to become distorted. Then, as the coating extrudes from the parting line faces, the bearing loses its tight fit in the housing causing additional problems.”
One of the best stories about the benefits of using coated engine bearings came from Dan Swain of Swain Coatings, Scottsville, NY. “Back in 1993, we started coating engine parts for a number of NASCAR teams. We coated a set of bearings for Alan Kulwicki, who was running in a NASCAR race at Martinsville. Part way through the race, Alan’s motor threw the belt for the oil pump drive and he lost all oil pressure. But he kept going and ran another four or five laps. When a caution flag came out, he went into the pits and had his crew replace the oil pump belt. The engine was still running great and he went on to finish the race. The coating on the bearings saved the engine and helped him win the championship later that year.”
Swain said coated bearings are a great insurance policy against oil starvation and dry starts on any engine application, not just racing engines.
To do tons of coated bearings for heavy-duty diesel engines. Many of these engines are typically rebuilt after 500,000 miles. Uncoated bearings typically develop a timing mark wear pattern at 2 and 10 o’clock that eventually leads to bearing failure. But when we replace these with coated bearings, the bearings will often go a million miles without a problem.”
Swain said coatings are not as easy to develop or apply as one might think. If not done correctly, the coating may flake off. Molybdenum disulfide and tungsten disulfide are both extremely tough coating materials that can withstand pressures of up to 350,000 psi without deforming or galling. They also hold oil rather than repel it to improve lubricity. But either material alone won’t stick to a bearing surface. The active ingredients must be held in a polymer matrix that has a pseudo-metallurgical bond with the bearing.
“We activate the bearing surface so the coating will adhere to it, and spray on the coating with a robot. The coating is heated as it is applied, which crosslinks the matrix and bonds it to the metal. The coating we apply is only .0002? thick, so it isn’t necessary to compensate for the thickness of the coating when select fitting the bearings. You can run tighter tolerances with the coated bearings,” said Swain.
Jerry Ehlert of Calico Coatings, Denver, NC, offers similar advice. “We apply a .00025? to .0003? coating of moly and teflon, which allows a slightly tighter fit than normal. In our experience, the coating extends bearing life anywhere from two times to 10 times over that of an uncoated bearing in racing applications. We’ve heard numerous stories from racers who have lost oil pressure and continued to run several laps without wiping out their engine thanks to coated bearings and pistons. It really can make a difference.”
Ehlert said Calico offers coated bearings for both domestic and import applications, including many sport compact engines such as Honda, Mazda, Mitsubishi, Subaru and Toyota. “We buy bearings from other manufacturers and coat them with our proprietary material. We’ve been doing this for 20 years and have had great results.”
Whether coated bearings are right for you or not depends on the kind of engines you’re building (stock or performance) and how much your customers are willing to spend for the added protection afforded by coated bearings. For most applications, a coating adds less than $100 to the cost of the bearing set. That’s cheap insurance considering what a warranty claim due to a dry start or loss of oil pressure might cost.
For information on suppliers of engine bearings, access the online Engine Builder’s Buyers Guides, exclusively at our Web site, www.engine-builder.com.