Auto Service World
Feature   October 1, 2008   by Jim Anderton Technical Editor

canadian automotive technician (October 01, 2008)

Bearing the Load; Engines are smaller, but the stress on engine bearings is higher than ever

As modern engines are expected to generate more power at higher RPMs with good economy, internal stresses are higher than ever. Add cooling systems with little reserve capacity and lower oil capacity, plus thinner oils and the main and rod bearings are ripe for failure, especially in poorly maintained engines. A surprising number of techs, however, will chase a low oil pressure issue with a pan drop and quick replacement, especially of connecting rod bearings. There are important questions about maintenance and troubleshooting when bearings are at issue … for the answers, SSGM consulted Raymond King, director, engine parts marketing, Aftermarket Products and Services for the Federal-Mogul Corporation:

Q Do extended oil drain intervals have implications for premature bearing wear?

A This is primarily a concern only in severe-service applications where the engine is exposed to increased operating temperatures and dirty conditions. Today’s engine oils certainly enable longer replacement intervals, in that the chemical properties won’t break down. But the chief concern from a bearing perspective is the presence of particulate contaminants in the oil. In dirty, dusty conditions, you’re more likely to introduce this particulate matter into the engine, which can cause premature bearing wear. The key is to make sure your filtration system -oil and air filters -is in good shape and that the engine is adequately sealed.

Q Is the use of a wrong oil grade a potential cause of bearing wear/failure?

A Absolutely. Today’s light-vehicle engines are very durable, but they do have fixed operational limits and very tight internal tolerances. The vehicle owner and technician should always follow the engine manufacturer’s lubrication specs. In regard to bearing life specifically, the failure to follow the OEM’s specification could impact the oil film separating the bearings and crankshaft, potentially causing direct contact between the mating surfaces.

In some cases, the engine manufacturer will recommend a petroleum-based oil and a synthetic alternative. A reputable synthetic oil will maintain its molecular structure over a longer period than a conventional oil. Synthetics also offer enhanced anti-friction properties that can help increase engine efficiency and longevity. Of course, they are significantly more expensive than conventional oils, so the consumer needs to weigh the cost versus the likely benefit, given his or her driving situation.

Q Can indiscriminate use of aftermarket oil additives cause early wear/failure of engine bearings?

A They key word is “indiscriminate.” There are some very good additive products on the market, and there are others that make highly implausible claims. In general, it’s best to stick with a brand and manufacturer you know and trust. If a product carries a claim that doesn’t seem realistic, I’d avoid it. In terms of bearing wear, there are some additives that feature a cleaning agent that can increase friction. There are others that claim to reduce smoke, but which can affect oil pressure due to build-up in some locations within the engine. These products could conceivably have an impact on the service life of the bearings.

Q Modern running clearances are much tighter today. Is Plastigage still appropriate for these engines or should techs “mike” the journals?

A Plastigage is a great product for a lot of engines, but as tolerances get tighter I would always “mike” the journals to prevent a potential comeback.

A It is more difficult to eyeball aluminum bearings – primarily because you won’t see material that’s been removed from the overlay -but you can spot damage if you know what you’re looking for. A heat issue will normally blacken the bearing face. You might also see a smear pattern on the face, which means there’s been unwanted contact between the bearing and crank.

Q Wear in aluminum bearings is thought to be harder to spot compared to babbit/copper underlay designs. Can technicians tell anything by eyeball today?

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