Engine Bearing Supplier Questions & Answers – Engine Builder Magazine


As for the order of importance for the connecting rod and the main bearings, they are at the very top. The work they do is endless and requires a lot of heavy work and multiple repetitions.

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It’s hard to believe that such small shell-like parts can be responsible for so much in the life of an engine, but that’s the way it is. They must withstand high pressures on a thin film of oil (between 0.0001˝ and 0.0004˝ thick) between the crankshaft journals to prevent metal-to-metal contact.

We spoke to a few motor bearing manufacturers to ask them about the latest in bearing technology.

Q: When building a high performance motor, when should you go for a stronger bearing material? Is there a power range for specific bearings?

According to Dan Begle, MAHLE Aftermarket Inc., several factors determine this. “If the customer is using an ‘H’ cover bearing and it indicates cover fatigue, we recommend building it using our ‘V’ cover material. If this is a known high horsepower motor that will be frequently serviced, we recommend starting with the V-stack material. A general guideline for using V-series bearings is around 1 500 hp. If you don’t know which type of performance bearing to start with, the H-series bearing will be your best bet.

Begle further explains that if you are using a V-series bearing, “you have to compensate your clearances for crank flex, more block flex, etc. With the copper-tin-lead bearing, the H-bearing, you don’t produce as much power, so you don’t have as much warping. For example, most drag racers run clearances a bit larger than stock to keep the oil viscosity moving enough oil to cool the bearing. If you don’t cool the bearing, you start to melt the properties of the coating.

Ron Sledge of King Engine Bearings says it’s a good idea to go for a heavier duty performance bearing when you hit 500-600hp and beyond. Depending on how long the load takes, King’s strongest bearing can handle up to 4,000 hp.

Q: Do racing motor bearings need a Babbit coat? If so, what is the Babbit layer for these applications?

Begle says all bearings need a Babbit or coating. “The purpose of having the Babbit or overlay is to create a surface that resists galling, has conformability to crank deformation and cylinder pressures, and incorporation for debris.”

According to Sledge, the Babbitt top layer is the forgiving layer of the bearing. “High performance tri-metal bearings are designed with a thinner than normal Babbitt layer. The Babbitt is also reinforced by adding more copper for increased tensile strength. This is to prevent what is called layering fatigue.

Q: When engine builders install new racing or performance style bearings for the first time, what are your recommendations for installing them correctly?

Begle says, “The two main factors are creating the correct housing bore diameter to allow the bearing to have the correct amount of contact pressure to hold the bearing in place. The second factor is to set the correct oil clearance to allow proper hydrodynamic oil shim for the crankshaft/bearing interface.

Sledge says, “Make sure the bearing clears the crank thread. You must obtain the correct oil clearance for the application and oil viscosity. (See side table below).

Q: What is your position on coatings? Are they a good idea, a personal preference or does it depend?

“I’ve seen great results with coated bearings,” says Begle. “They reduce friction when the oil film is compromised and significantly reduce bearing overlay temperature.”

Sledge says, “Coatings are like buying insurance. They work great when you need them. Coatings help the bearing survive when the lubrication system fails.

Q: If you add a coating to the bearing does it change your clearance or do you have to use the same clearance fit as an uncoated bearing?

“Yes, the clearance will decrease from a coated bearing to an uncoated bearing,” says Begle. “Adjustment play must be done with the bearings that are installed. Our coated bearings will have less play than our uncoated bearings.

Sledge says, “King coated bearings are made with no extra thickness. So a coated bearing has the same oil clearance as the uncoated bearing for the same size. »

Q: What are the most common causes of bearing failure for stock and performance applications?

Begle notes that there are several factors to this, “but normally on stock engines it’s debris and on performance engines it’s loss of the oil film.”

Sledge says the main causes of failure they see are “foreign debris and insufficient oil film strength.”

Q: When do stem bolts need to be upgraded?

Begle says upgrading the connecting rod bolts helps “decrease big end warping of the connecting rods.” The key to any bolt/stud upgrade is to make sure the new clamp load has no not affected the housing bore. Break-in should be done after leveling.

Sledge recommends using upgraded connecting rod bolts whenever the average engine rpm exceeds the stock rpm limit.

Q: During engine break-in, what is the best procedure to ensure the bearings are in good condition afterwards? Do the rods need to be tightened? Do you want to remove a plug and see the condition of the bearing?

Begle says the best procedure is to analyze the oil filter media. “There is no need to tighten the rods because the stretch of the bolt does not change due to metal-to-metal surface contact.”

According to Sledge, “After break-in/break-in, drain the break-in oil and inspect the bearings. If all looks good, replace with new racing oil without break-in and continue to monitor the oil pressure on the dyno.

Q: When it comes to filtration, most failures seem to be related to a contamination issue. Should engine builders break in the engine with a low micron filter, or is a mesh style race/performance filter enough to catch all the debris?

Begle says, “Normally I don’t use a different micron filter for break-in. Using a micron filter that is too small can reduce oil flow and create other problems. A proper micron filter will always let particles through. These particles can normally pass through a bearing with minimal damage.

But Sledge says you should use a low-micron filter to break-in the engine, then switch to a racing filter or whatever you use during normal operation.

Q: What does bearing eccentricity mean and how does it affect stock and performance?

Seldge says, “The eccentricity is the taper in the bearing wall of the crown at approx. 3/8 inch from part line. This reduction in wall thickness is responsible for the formation of the oil film wedge which lifts the trunnion from the bearing surface.

Begle notes that eccentricity is “the amount of runout from just beyond the relief of the bore to the thickest part of the bearing (12:00 – 6:00 position). The purpose of eccentricity is to help generate the hydrodynamic wedge, which keeps the crankshaft off the bearings.

Sledge says the bearing design features motor builders should keep in mind when selecting bearings for your applications is whether to use the tapered or chamfered style. “Most are narrow bearings today,” he says. “But you need consistent bearing thicknesses to keep the desired oil clearances stable.”

Begle adds that their M material, the Babbitt material, is primarily used for the thrust surface. “The thrust surface is actually the substrate, so the substrate doesn’t give enough for the thrust. Most people who run the M-series on a drag application do so because of the thrust. Lots of Pro Mod guys they execute “V” shells and they execute an “M” thrust, it’s because of the thrust flanges.

Begle adds that you can mix and match the bearings depending on your needs for the application. We sell a ‘VM’ kit, which is the V shells and the M thrust. This way you get the durability of the hulls as the V hulls will be better from a load point of view. M thrust is better from a thrust perspective, but especially with converter cars and so on, if the converter swells too much it will fail if you don’t have enough thrust. This adds a margin of safety.

As most readers know by now, not all engine builders agree on the same practices and procedures to achieve the desired result. Veteran builders usually understand what has worked for them in a specific situation in the past and can use it in the future, but that doesn’t mean there aren’t other methods that will achieve the same result. or a better result.

Just like every engine builder, different manufacturers have different philosophies for getting the most out of their products or components. Although there are some differences of opinion, there are also many similarities. It is ultimately up to you to use your best judgment. But if in doubt, don’t hesitate to call your bearing manufacturer for their suggestions and recommendations for your particular application. You can learn something that works better than your way. BE


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