All You Ever Wanted To Know About Engine Bearings
Updated October 2, 2013
When it comes to vehicle engines, it’s all about the crankshaft. The shaft is what the pistons spin around, and without a fully functioning crankshaft, the engine will not work.
To keep the crankshaft spinning freely, the crank spins on specially designed bearings that are so fundamentally important they’re called “engine bearings.” To guarantee smooth operation, efficient performance, and durability, engine bearings are carefully designed and manufactured.
Here’s everything you ever wanted to know about engine bearings. When you’re done reading, you’ll be a bearing expert (well, almost an expert).
Engine Bearing Design and Construction
Engine bearings come in light, intermediate, and heavy-duty varieties, depending on the application. Most bearings use bimetal or trimetal construction. Bimetal bearings use a single multipurpose lining with a steel backing for support. The single multipurpose lining on a bimetal bearing is usually a copper-lead or aluminum-based alloy mixed with babbitt, which is a special alloy that features a high percentage of lead or tin. Most bimetal bearings do not have an overlay, which allows for tighter tolerances and a lower friction coefficient.
Trimetal engine bearings feature an overlay of babbitt on top of an intermediate lining of aluminum or copper-lead, with a steel backing providing support. Heavy-duty engine bearings employ babbitt as a thin protective material overlaid on an intermediate layer consisting of cast or sintered copper-lead.
Without lubrication, a bearing will quickly overheat and weld itself to the crankshaft. Therefore, bearings and cranks are designed so that the crank rides on an incredibly thin protective film of oil that separates the crankshaft and the bearing surface from one another. This protective film is only generated while the shaft rotates, as the spinning crankshaft is the mechanism for oil dispersal.
As the oil is circulated throughout the engine via oil pump, it fills in the space between the bearing clearances, allowing the shaft rotation to pull oil in between the shaft and the bearing.
It’s often surprising to find out the survival of the average engine bearing depends on a .0002-inch thick film of oil. What’s worse, when your engine really needs a good layer of oil to protect the crank and bearigns – such as at high operating temperatures and/or under heavy loads – the increased crank rotation speed further reduces the thickness of the oil film.
Bearing Failure Modes
Lack of lubrication is the most common cause of bearing failure. In the event that the protective oil film dissipates, the bearing becomes subject to metal-on-metal contact with the shaft. At high rotation speeds, the bearing can experience a phenomenon known as “wiping,” where the bearing surface is polished by contact with the shaft. Heat from the friction caused by metal-on-metal contact follows shortly, eventually escalating into complete seizure of the bearing, shaft and as a consequence, the engine itself.
Bearings can also fail due to fatigue caused by loads transmitted repeatedly through the oil film. Any metal will eventually experience fatigue if it’s subjected to enough load cycles for an extended period of time. Metal-to-metal contact is not necessarily required to bring about metal fatigue, although wiping can be triggered by periods of extreme loading.
Other ways an engine bearing can fail include:
- improper mounting
- electrical damage that results in pitting or cratering of the metal
- oil contaminants can embed themselves in the surface of the bearing, depending on the overall softness of the metal and the stresses applied to the bearing itself
How To Make Sure Your Engine Bearings Last As Long As Possible
Generally speaking, the best way to ensure that your engine bearings last is to use the oil recommended by your vehicle manufacturer and to follow the recommended service interval. Additionally, it’s important to invest in a good quality oil filter. Wix is a trusted after-market oil filter brand, and most OEM oil filters are top quality too.
Whatever you do, avoid cheap after-market oil filters, as they can provide inadequate protection from oil contaminants. The $2 you save buying a “Brand X” oil filter won’t come close to covering the cost of a damaged engine.
Finally, while most repair shops and auto dealers recommend a 3,000 mile oil change interval, this may be overkill. If you use a good quality oil filter and the recommended oil, most newer vehicles can go 5,000 to 10,000 miles between oil changes, depending on driving conditions.
About the Author: Jason Lancaster is the founder of TundraHeadquarters.com, a website for Toyota Tundra enthusiasts. Jason also helps to promote Olathe Toyota Parts Center, an online retailer or genuine Toyota Parts.
Categories: Gear Grinding