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Part one of our engine bearing series covered the technical side of how bearings are are engineered and what materials they are made from. In this segment, we get a little more hands on by discussing how bearings wear and how to diagnose problems with engine bearings. Once again, we have enlisted our experts from King Engine Bearings and MAHLE Clevite to give us the straight scoop on the how’s and why’s of bearing replacement.

The Experts

We listened to two highly respected authorities in the field, Dr. Dmitri Kopeliovich, Research and Development Manager of King Engine Bearings and Bill McKnight, Team Leader of Training at MAHLE Clevite, as they educated us on bearing technology. Between Kopeliovich and McKnight, there is over a half century of experience in engine bearing technology. Needless to say, these guys have seen it all.

Engine Bearings Have A Story To Tell.

Rebuilding a blown motor may end up being a habit unless you take the time to diagnose the problem. According to Clevite’s Bill McKnight, “If a mechanic merely replaces a damaged bearing in an engine without determining the cause of it’s failure, over 99% of the time he will be subjecting the replacement bearing to the same cause that was responsible for the original failure or distress.”

Abrasive wear occurs when a harder material is rubbing against a softer material and can take place with or without foreign bodies present.

We take McKnight’s statement to mean that if you are doing the same thing without changing anything other than the consumable parts, don’t expect a different result. If anything, you should always be looking to improve your engine’s performance, so reading the wear on your engine bearing is a necessity in order to make your engine program better.

When a bearing is replaced, it’s important to take a close look at the old bearing and diagnose any problems. Understanding what type of wear the bearing is experiencing cam help a technician solve any future problems before they ever exist to a point where engine damage can occur.

King Engine Bearing’s Dr. Dmitri Kopelivoich explained the most common types of wear associated with engine bearings:

Abrasive wear. This is surface on surface wear. It can also be three body wear when a particle is involved, like when a camshaft lobe is being ground flat and the particles make their way through the oil system.

If there are only two rubbing parts involved in the friction process the wear is called two body wear. In this case the wear of the softer material is caused by the asperities on the harder surface.

If the wear is caused by a hard particle (grit) trapped between the rubbing surfaces it is called three body wear. The particle may be either free or partially embedded into one of the mating materials.

Adhesion wear is a result of micro-junctions caused by welding between the opposing rough surfaces rubbing on the counterbodies. The load applied to the contacting surfaces is so high that they deform and adhere to each other forming micro-joints. The motion of the rubbing counterbodies result in rupture of the micro-joints where some of the material is transferred by its counterbody. This effect is called scuffing or galling. Eventually this will cause the seizure of one of the bodies by the counterbody.

Adhesive wear. This is when the two surfaces begin to fuse together or bond and pieces are torn off of one of the surfaces and bonded to the other.

Fatigue wear. Can be caused by cycle loading, gasous bubbles forming in the oil or particles which attack the bearing material and low oil pressure.

Corrosive wear. Wear that is accelerated by corrosion or oxidation.

Erosive wear. Wear caused by impingement of particles which remove fragments of material from the bearing surface.

McKnight breaks down the wear factors even further by saying that MAHLE Clevite’s analysis have shown “45.4 percent of bearing distress is caused by dirt. 12.8 percent is caused by misassembling the components, 12.6 percent is due to misalignment, 11.4 percent of bearing problems from insufficient lubrication with only 8.1 percent from overloading.”

Bearing Installation issues

Using the data collected over the years from King Engine Bearings and MAHLE Clevite, several issues have been identified relating to installation of the bearings. Knowing these problems exist are valuable in eliminating future problems in your next engine build.

Dirt on either side of the bearing can cause problems.

Dirt. Dirt is an engine’s worse enemy! When it comes to bearings, take every effort to remove any presence of foreign material from the bearing back and the housing. Wipe down the bearing surface after installation.

Reversed position of the upper and lower main bearings. There is a common mistake that should not be made, even by the most rookie of engine builders. According to Dr. Kopelivoich, it happens more than you would think.

When a bearing has failed due to oil starvation, its surface is usually very shiny. In addition, there may be excessive wear of the bearing surface due to the wiping action of the journal. In the most severe cases the bearing surface will be smeared or scratched and torn. The bearing will begin to turn dark blue to black in color. Probable causes for this condition are misassembling main bearings and lubrication system not primed before start up (Dry start)..

Dry start. Using assembly lube and priming the oil system before attempting the first start on a fresh engine solves this problem.

Misalignment and distortion. Remember when the machinist asked if you wanted the main bearings housing line honed and you saved a couple extra bucks by skipping that procedure? One word: DON’T. Have the bearing housings checked and also have the individual components checked to make sure the connecting rods are not twisted, the crankshaft is not distorted and all components are within specifications.

Misalignment and distortion problems can come from bearing cap shift, bent crankshaft, bent connecting rods or bearing housing distortion.

Presence of abrasive particles on shaft surface or in oil passages. If you are replacing your engine bearings, it’s likely that you have taken the extra time to have the block steam cleaned. It pays to have the machinist do a good jet wash and pay attention to the oil passages. When the crankshaft comes back from being ground or balanced, make sure the machinist runs that through the cleaner too.

Crankshaft journals ground out of shape will cause serious problems with bearing failure.

Out of shape grinding of crankshaft. Oy Vey! Use only trusted machinists with a good reputation. Nothing is worse than letting a new machinist try their freshly learned skills out on your crankshaft only to have a hourglass, tapered or barrel shaped journal. If it is not too bad it can be ground undersized but many times the only solution is a new crankshaft.

Installing New Engine Bearings

One of the most frequently asked questions that bearing manufacturers get is: “How much clearance do I need for my connecting rod bearings or main crankshaft bearings?” A very good question but not an easy one to answer. The importance of bearing clearance is almost self evident. Because the rotating shaft rides on a film of lubrication, the greater clearance between the rotating shaft and the bearing means that there will be less oil surface contact. Less clearance means almost certain engine death without the proper amount of lubrication to support the rotating shaft.

Torres starts by measuring all the journals on the crankshaft and recording the measurements.

Engine application, lubricant selection and operating conditions all play a crucial role in clearance. There is no “one size fits all” rule. Checking with the crankshaft, rod or camshaft manufacturer or working with your engine builder is the best practice for determining what your bearing clearance should be.

We checked with our local machine shop, Torres Performance and Machining, and talked with shop owner Joe Torres about measuring bearing clearance. Torres had some handy tech tips that help get accurate and repeatable results when measuring bearing clearances.

Using the measurements from the crankshaft journal, Torres zeros out the bore gauge to measure the bearing in the housing.

According to Torres, climate control is important. “In the inland empire region of Southern California we have large temperature swings from morning to mid day and again from mid day to evening. Different metals expand and contract at different rates in relationship to the temperature, so it’s important to have a climate controlled clean room to perform the assembly and measure clearances,” said Torres.

“It’s also important to have a set procedure. Doing the same thing, the same way, for each cylinder will ensure precise and accurate measurements. This goes for using the same assembly lube on the entire bearing set all the way to using the same torque wrench to tighten the bearing caps,” he added.

Main bearings are installed in the bearing housing and the caps are torqued down. Torres says that the bearings, caps and housing must all be clean of debris and oil free.

Torque wrenches and bore gauges are precession measuring devices that can lose their ability to accurately measure things like torque and distance, especially if they are dropped or abused. Making sure that the equipment that is used for the assembly is in current calibration can go a long way to achieving perfect results.

Torres explained the procedure his crew uses for engine bearing replacement: “We began by tearing down the engine and taking a close look at the parts that we removed. Engine bearings specifically can tell us a lot about the engine. When the block is cleaned and machined, we measure each bearing housing and document the measurements so that we know what we are working with. We don’t even order a set of bearings until we get the crankshaft so that we can measure the journals and order the right set of bearings the first time.”

Torres uses the bore gauge to measure the installed bearing's inside diameter.

When the bearings arrive, Torres says that the crew does a complete dry assembly using plasti-gauge to verify the bearing clearances. According to Torres, “we usually use the bearing manufacturer’s tolerances on bearing clearance because each crankshaft manufacturer has their own way of grinding journals. The bearing manufacturers have a pretty solid set of specs when it comes to clearances for each application.”

Torres rechecks the clearance using plastigage. After laying a piece of the plastigage across the journal, Torres installs the bearing cap and torques it to appropriate torque specs. Removing the cap shows that the plastigage has been smashed to the height of the oil film clearance. Torres uses the gauge supplied with the plastigage to check the dimension for proper clearance.

Problems and Coatings. Can you just “cover it up”?

There has been a lot of information floating around for several years about coatings. The more we find out about coatings, the more we like them. Here’s what our expert’s had to say about the subject:

McKnight: “We find our customers have strong feelings about coatings. They either love coated bearings, or wouldn’t use one if it was given to them free!

Almost all bearing coatings provide an anti-friction layer to the bearing and are intended to increase the bearing life in very marginal oil film conditions by preventing the transfer of the bearing face material (babbitt or aluminum) to the crankshaft. These marginal oil conditions can exist under heavy operation loads seen in racing and performance engines, but also may be present when an engine in a street rod is started for the first time after sitting all winter. Since damage to the face material of a bearing is permanent, this protection is deemed a good thing by coated bearing advocates.

Detractors of coated bearings point out that the coating layer, some .0003″-.0004″ thick, wears away, increasing the bearing to crankshaft clearance. Increased bearing clearance on performance engines concentrates the firing load on a smaller area of the bearing, increasing both the pressure on the oil film and the likelihood of bearing failure.

Both sides are dug in pretty deep, hence our offering of both coated and uncoated performance bearings.”

An uncoated H series bearing on the left and a coated H series bearing on the right.

Dr. Dmitri Kopelivoich: Coatings can help to eliminate or reduce metal-to-metal contact between the bearing and the journal surfaces during start-up and the initial period of bearing operation. Coating promotes conforming of the bearing surface resulting in lower wear of the bearing material.

Components of coating have excellent anti-friction properties (very high seizure resistance, low coefficient of friction, embedability, conformability). However, coatings are a sacrificial layer. They can wear fast under high load (metal-to-metal contact). When the coating is removed by friction, the bearing clearance is increased by the value of the coating thickness. Therefore, coatings should not be too thick (not more than 0.0004”/0.01mm). Coatings have no effect on bearing load capacity.

The Final Word.

Like we explained in the opening, there’s more to engine bearings than meets the eye, and we’ve just scratched the surface of engine bearings. When it comes to checking, buying or installing these half shell bearings, details can mean the difference between a high performance engine that lasts or one that eats itself up in 20 minutes. The bottom line is; a little extra effort, knowledge and attention to detail pays big dividends once the engine is under the hood.