Engine Problems Explained: Spun Bearings

Spun bearings may not sound like a serious issue, but it’s one of the last phrases you want to hear from your mechanic. It refers to when the bearings inside your connecting rods break and start to spin with the crankshaft. This can occur from a variety of factors and the result is usually a complete engine rebuild.

What Does It Mean To Spin A Bearing?

The connecting rod in your engine links the piston to the crankshaft. On the crankshaft end, a pair of shell bearings protect the rod as the crank rotates. If the shell bearings wear thin, they can shift position or rotate with the crank, causing severe engine damage.

Why Would An Engine Spin Bearings?

“This [engine] spun a bearing which is what completely rocketed those connecting rods to pieces and those pieces were rattling around inside the block there for a bit…so this is a very extreme example of what spinning a bearing would look like …some interesting damage!“

• Overrevving when cold
• Very high mileage
• Poor servicing
• Modifying engine components
• Manufacturing defects (PPI corrects all factory defects)
• Overheating
• Bearing design insufficient for the engine

Most engines last for years with no bearing issues. However, if they aren’t maintained properly, are regularly driven hard, or are modified, the bearings can eventually fail.

Sometimes, even a well-maintained engine can spin a bearing due to a factory defect or simply from having accumulated very high mileage.

What Happens When Your Engine Has Spun Its Bearings?

In some cases, spun bearings can be heard as a knock. In many cases, spun bearings cause the connecting rods to snap. In extreme cases, they break through the block. The video above shows what happened to an L99 motor after it spun its bearings.

This engine does not have counterweights in the center of the crank. The resulting vibration at high revs caused the bearings to seize, which in turn threw the rods. Read more about what it means to throw a rod here.

Can You Diagnose Failing Bearings?

Diagnosing spun bearings before they cause major issues is almost impossible without opening the engine up and inspecting it. Sometimes, small metal shavings can end up in the oil as the bearings are failing. But in most cases, the first time you know something is wrong is when the engine loses power and starts making loud knocking noises.

Try to turn the engine off as soon as possible. This can limit the damage and perhaps save the block, connecting rods, and pistons.

What Can You Do To Prevent Spun Bearings?

As with most engine-related issues, regular maintenance and a measured driving style are key. They can greatly extend the life of your vehicle’s mechanical components. Nothing will guarantee that you won’t suffer from spun bearings, but the following suggestions can lower the risk of it happening:

• Follow the manufacturer’s service intervals
• Don’t drive aggressively or over-rev the engine
• Wait until the engine oil is warm before driving enthusiastically
• Stick to good quality fuel and oil
• Avoid modifying your engine

At PPI we don’t just rebuild engines, we also rectify any known factory faults. This can help extend the life of your remanufactured engine. If you plan on modifying your engine, make sure that the internals are up to the extra stress and extra heat. The added heat can often cause cooling issues and eventual engine damage.

Choose Powertrain Products For Quality Remanufactured Engines

Whether your engine knock means you need a replacement motor or just a rebuild, Powertrain Products is ready to help. We stock a huge range of over 3000 rebuilt and used engines.

All our remanufactured engines are fully assembled and updated to correct any factory faults. We offer a 3-year standard warranty on all of our engines. That standard warranty can be upgraded to 5 or 7 years or 1 million miles, whichever comes first.

We’re also the nation’s leading supplier of differentials, transmissions and transfer cases. Call us at 888-842-0023 or contact us online. Our friendly staff will help you find the perfect replacement part in no time.