Connecting rod bearings are an essential component of internal combustion engines, helping to transfer the power from the piston to the crankshaft. However, these small but vital components often go unnoticed until they fail, causing catastrophic damage to the engine. In this blog post, we’ll take a closer look at connecting rod bearings, how they work, common causes of failure, and tips on how to maintain them to keep your engine running smoothly. Whether you’re a car enthusiast or just curious about how engines work, read on to learn more about this crucial engine part.
Table of Contents
What are connecting rod bearing?
Connecting rod bearings are small cylindrical components that connect the connecting rod to the crankshaft in an internal combustion engine. They are typically made of a high-strength alloy and are designed to withstand the tremendous forces generated by the engine’s operation. The bearings act as a buffer between the connecting rod and the crankshaft, providing a smooth and durable surface for the two parts to move against each other.
The bearings work by reducing friction between the moving parts, allowing them to move more efficiently and with less wear. They also help to distribute the load from the piston evenly across the crankshaft, ensuring that the engine runs smoothly and without vibration. Proper lubrication is crucial to the performance and lifespan of connecting rod bearings, as they must be constantly lubricated to prevent excessive heat buildup and wear.
What is the function of connecting rod bearings?
The primary function of connecting rod bearings is to provide a smooth and durable surface for the connecting rod to move against the crankshaft in an internal combustion engine. This allows the engine to transfer the power generated by the combustion process to the crankshaft, which then turns the wheels and propels the vehicle.
The bearings also help to distribute the load from the piston evenly across the crankshaft, which is important for ensuring that the engine runs smoothly and without vibration. Additionally, the bearings reduce friction between the moving parts, which helps to increase efficiency and reduce wear.
Types of Connecting rod Bearings
There are several types of connecting rod bearings, including:
- Bi-metallic bearings: These bearings consist of a steel backing with a layer of soft metal, such as copper or aluminum, on the bearing surface. They are commonly used in modern engines due to their durability and resistance to wear.
- Tri-metallic bearings: These bearings consist of a steel backing with a layer of copper or aluminum, and a thin layer of lead or tin on the bearing surface. They offer excellent load-carrying capacity and resistance to fatigue and wear.
- Polymer-based bearings: These bearings are made of a plastic or composite material and are designed for low-load applications. They are lightweight, durable, and have a low coefficient of friction.
- Copper-lead bearings: These bearings consist of a copper-lead alloy on the bearing surface and are commonly used in older engines. They offer good wear resistance but may require more frequent replacement than other types of bearings.
- Aluminum bearings: These bearings consist of an aluminum alloy and are used in some high-performance engines. They offer good wear resistance and are lightweight, but may not be as durable as other types of bearings.
The type of connecting rod bearing used in an engine will depend on the specific application, load requirements, and manufacturer’s specifications.
CAUSES OF BEARING FAILURES
Contamination often leads to premature bearing failure. If dirt or other abrasives get between the crankshaft journal and the bearings, they can become buried in the soft bearing material. The softer the bearing material, the better the embeddability. This may or may not be good, depending on the size of the abrasive particles and the thickness of the bearing material.
If the particles are small and deeply embedded in the relatively soft bearing material, they will not damage the crankshaft journal. However, displacing the surrounding bearing material or protruding from the bearing surface can damage the crankshaft. Heat is another factor that accelerates bearing wear and can lead to failure if the bearings get hot enough.
Bearings are cooled primarily by oil flow between the bearing and the journal. Restricting or reducing oil flow not only increases bearing temperatures, but also increases the risk of scratching or scuffing the bearings. Conditions that can reduce oil flow and cause bearings to overheat include worn oil pumps, clogged oil pickup screens, internal oil leaks, low crankcase oil level, aeration oil (oil level too high), Excessive dilution by fuel Blow-by of oil. Or coolant contaminated oil due to internal coolant leak.
Temperatures above 620 degrees can melt copper/lead and lead in Babbitt plated bearings. Copper only melts at 1,980 degrees, so fired copper/lead bearings usually have a copper look instead of the usual dull gray look.
Misalignment is another condition that accelerates bearing wear. If the center main bearing is wearing more than the ends of the crankshaft, you may have a bent crankshaft or misaligned main bore.
Crankshaft straightness can be checked by placing the crank in a V-block, placing a dial indicator on the center journal, and observing the reading while rotating the crank one full revolution. If the runout exceeds the limit (the larger the shaft diameter, the greater the maximum allowable runout), the crank should be straightened or replaced.
When installing and tightening the main cap, you can check the alignment of the main bore by inserting a rod approximately 0.001 inch smaller in diameter than the main bore into the block. If the rod doesn’t turn easily, you’ll need to drill the block in a straight line. You can also check alignment with a straight edge and feeler gauge. Deviation greater than 0.0015 inches. Each hole should be aligned. Line drilling is also required when replacing the main cap.
Concentricity of the main holes is also important and should be within 0.0015 inches. Otherwise, re-boring is required to install a bearing with an oversized outer diameter.
Connecting rods with slotted holes in the big ends can cause similar problems. Oblique or uneven wear patterns on rod bearings usually indicate twisted rods. An extended crankpin bore or twisted rod should be rebuilt or replaced. On some newer engines with powdered metal rods and “cracked” caps, such as the Ford 4.6L V8, the caps do not have machined mating surfaces, so rods with elongated bores require the caps to be ground. It cannot be reworked. So the connecting rod bearing bore should be cut to accommodate the oversized he OD bearing if the bore is not stretched or rounded.
Uneven bearing wear due to misalignment can also occur if the crankshaft journal is not round. To check crankpin roundness, measure the diameter of each pin at either bottom dead center or top dead center, then measure again at 90 degrees in both directions. Rod journals usually wear the most at top dead center. Comparing the diameters at two different locations should reveal the roundness. The conventional rule of thumb says 0.001 inch max. Journal deviation is acceptable, but many of today’s engines cannot tolerate run-out greater than 0.0002 to 0.0005 inches.
Check journals for taper wear (one end is worn more than the other), barrel wear (ends are worn more than the center), or hourglass wear (the center is worn more than the center) To do so, measure the diameter of the journal at the center and ends. Again, the generally accepted wear limit for cones used to be 0.001 inch, but today ranges from 0.0003 to 0.0005 inch for cones 2 inch diameter and larger.
The journal diameter itself should be within 0.001 inch of the original dimension, or within 0.001 inch of the standard reground dimension to ensure proper oil clearance for the replacement bearing. If the magazine has been previously reground, it will usually have the machinist’s mark stamped on it. A 10, 20, or 30 means that the crank has already been ground to an undersize and does not need further resharpening as the crank wears.
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What is Connecting Rod Bearing Siezure?
Connecting rod bearing seizure is a condition where the bearing becomes stuck or welded to the crankshaft journal in an internal combustion engine. This can happen due to a lack of lubrication, excessive heat buildup, or prolonged wear of the bearing. When the bearing seizes, it prevents the crankshaft from rotating freely, which can cause significant damage to the engine.
The metal-to-metal contact between the bearing and the crankshaft journal can cause the bearing to heat up and expand, ultimately causing it to seize. This can result in the engine making unusual noises, decreased power output, or even complete engine failure. In some cases, the seized bearing can also cause damage to other engine components, such as the connecting rod or crankshaft.
Connecting Rod Bearings Siezures
Connecting rod bearings can seize for several reasons, including insufficient lubrication, excessive heat buildup, and wear from prolonged use. When a connecting rod bearing seizes, it means that the bearing has become stuck to the crankshaft journal, preventing it from rotating freely. This can cause significant damage to the engine and result in costly repairs.
Insufficient lubrication is one of the most common causes of connecting rod bearing seizures. When the bearing is not properly lubricated, the metal-to-metal contact between the bearing and the crankshaft can cause excessive heat buildup, which can lead to the bearing seizing.
Excessive heat buildup can also occur if the engine is running at high speeds for prolonged periods, or if the engine is overloaded beyond its design capacity. The increased friction and heat can cause the bearing to expand and become stuck to the crankshaft journal.
Wear from prolonged use can also contribute to connecting rod bearing seizures. Over time, the bearing can become worn down, which can cause it to lose its ability to properly distribute the load from the piston and crankshaft. This can lead to increased friction and heat buildup, which can ultimately result in the bearing seizing.
To prevent connecting rod bearing seizure, it is essential to maintain proper lubrication levels and perform regular oil changes. It is also crucial to avoid overloading the engine and to address any unusual noises or vibrations as soon as they are noticed. If a connecting rod bearing seizure is suspected, it is important to immediately shut off the engine and have it inspected by a qualified mechanic. Continued operation of the engine with a seized bearing can result in severe damage and costly repairs.
How to Change the Connecting Rod Bearing?
Changing connecting rod bearings in an internal combustion engine is a complex procedure that should only be performed by experienced mechanics. Here is a general overview of the steps involved in changing connecting rod bearings:
- Disconnect the battery and drain the engine oil.
- Remove the oil pan and the connecting rod caps. The caps are usually marked with an identification number, and it is important to keep them in order for reassembly.
- Use a plasti-gage or micrometer to measure the clearance between the connecting rod and the crankshaft. This will help determine the correct size of replacement bearings needed.
- Remove the old bearings and clean the bearing surfaces on the connecting rod and crankshaft with a soft, lint-free cloth.
- Install the new bearings, ensuring that they are properly aligned and seated in the connecting rod and crankshaft.
- Lubricate the bearings with engine oil and torque the connecting rod bolts to the manufacturer’s specifications.
- Repeat this process for all the connecting rods in the engine.
- Reinstall the connecting rod caps and torque them to the manufacturer’s specifications.
- Install the oil pan and refill the engine with oil.
- Start the engine and check for proper oil pressure and unusual noises or vibrations.
It is important to follow the manufacturer’s specifications and procedures when changing connecting rod bearings, as improper installation can result in engine damage and failure. If you are not experienced in engine repair, it is best to have a qualified mechanic perform this procedure.
How to check Connecting Rod Bearing Clearance?
Checking connecting rod bearing clearance is an important step in engine maintenance and repair. Here is a general procedure for checking connecting rod bearing clearance:
- Remove the oil pan and the connecting rod caps from the engine.
- Clean the bearing surfaces on the connecting rod and the crankshaft with a soft, lint-free cloth.
- Place a strip of plastic gauge or a micrometer on the bearing surface of the crankshaft.
- Replace the connecting rod cap and torque it to the manufacturer’s specifications.
- Remove the connecting rod cap again and carefully inspect the plastic gauge or micrometer. The plastic gauge will have flattened out to a specific width, while the micrometer will give a specific measurement.
- Compare the width or measurement to the manufacturer’s specifications. If the clearance is within the specified range, the bearings are properly seated. If the clearance is too tight or too loose, the bearings may need to be replaced.
- Repeat this process for all the connecting rods in the engine.
It is important to use the proper size of plastic gauge or micrometer and to follow the manufacturer’s specifications when checking connecting rod bearing clearance. If the clearance is not within the specified range, it can result in engine damage and failure. If you are not experienced in engine repair, it is best to have a qualified mechanic perform this procedure.
Connecting Rod bearing material
Connecting rod bearings can be made from various materials, but the most common ones are:
- Babbitt – a soft, white metal alloy of tin, copper, and antimony that is easy to pour and machine. Babbitt bearings provide a good balance of strength, durability, and resistance to wear.
- Aluminum – aluminum bearings are lightweight and have good thermal conductivity. They are often used in high-performance engines where weight reduction is critical.
- Steel-backed – steel-backed bearings have a steel shell with a layer of bearing material, such as copper or lead, bonded to the inside surface. They are commonly used in diesel engines and other heavy-duty applications.
- Polymer – polymer bearings are made from materials such as polyamide, polyester, or PTFE. They offer low friction, high wear resistance, and resistance to chemicals and corrosion.
The choice of connecting rod bearing material depends on various factors, including the engine’s operating conditions, the manufacturer’s specifications, and the performance requirements.
Blog Conclusion on Connecting Rod Bearing
In conclusion, connecting rod bearings are an essential component of an engine’s internal system. They play a crucial role in the smooth operation of the engine and help to transfer the force generated by the combustion process to the crankshaft. Regular maintenance of the connecting rod bearings is necessary to ensure the longevity and reliability of the engine.
One should keep a close eye on warning signs such as abnormal engine noise, reduced engine performance, or increased oil consumption, which could indicate a problem with the connecting rod bearings. It is recommended to replace the bearings whenever necessary, use high-quality bearings and lubricants, and follow the manufacturer’s guidelines for maintenance and inspection.
Failure to address issues with connecting rod bearings can lead to severe engine damage, expensive repairs, or even complete engine failure. Therefore, it is important to understand the role of connecting rod bearings and ensure their proper maintenance to keep the engine running smoothly and reliably.
FAQ on on Connecting Rod Bearing
Connecting rod bearings play a crucial role in the performance and longevity of an internal combustion engine. Without properly functioning bearings, the engine may suffer from decreased power output, increased fuel consumption, and even catastrophic failure due to excessive wear and overheating. Therefore, it is important to maintain and replace the bearings as needed to keep the engine running smoothly.
