What is a Crankshaft Journal?
A Crankshaft journal is a crucial component that helps transfer the piston’s linear motion into rotational energy. It serves as the contact point between the crankshaft and engine Bearings. There are two main types: main bearing journals and rod journals.
Common Crankshaft Journal Issues
- Excessive Wear: Often caused by poor lubrication or contamination. Symptoms include knocking noises and decreased oil pressure.
- Crankshaft Journal Damage: Surface cracks or scoring on the journals can lead to significant engine failure if left untreated.
Crankshaft Failure Symptoms
- Engine knocking or rattling sounds
- Sudden oil pressure drops
- Vibrations at certain RPMs
- Metal shavings found in oil
Function of Crankshaft Journals
The main job of crankshaft journals is to allow the crankshaft to turn the Pistons‘ up-and-down motion into rotational motion. The connecting rods transfer this motion to the crankshaft.
Lubrication and Protection
Both main and rod journals depend on oil for lubrication, preventing metal-to-metal contact. Oil flows through galleries in the engine block and the crankshaft. For rod journals, oil moves through holes in the main journals and out to the rod journals.
Precision and Durability
Crankshaft journals are carefully machined and polished to strict standards. Their surfaces are hardened to handle the high stresses of engine operation. The distance between the centerlines of the main and rod journals is called the crank throw or crank radius, which affects the engine’s stroke.
Engine Configuration
In inline engines, each rod journal typically serves one cylinder. In V-type engines, two connecting rods often connect to each crankshaft journal, creating an offset between the cylinders. V6 engines often use split-pin or split-journal designs to ensure even firing intervals. Some engines, like V-twin and radial engines, use articulated or forked connecting rods.
| Journal Type | Typical Material | Surface Hardening Method | Expected Service Life |
|---|---|---|---|
| Main Bearing Journal | SAE 4340 Alloy Steel | Nitriding | 200,000+ miles |
| Rod Journal | 38MnVS6 Special Steel | Induction Hardening | 150,000–200,000 miles |
Different Types of Crankshaft Journals
Crankshaft journals are key components that allow the crankshaft to rotate smoothly in an engine. There are different types, each with a specific function and design.
Main Journals
- Function: These journals are the main points where the crankshaft rotates. They are held in place by the main bearing caps and set the axis of rotation.
- Design: Main journals are fixed into the engine block and rotate inside main bearing saddles. These saddles contain replaceable bearings that are softer than the journals and can be replaced when worn.
- Lubrication: Main journals have oil holes that allow engine oil to flow through the crankshaft. This oil prevents metal-to-metal contact between the journals and bearings, keeping the engine running smoothly.
Rod Journals (Crank Pins)
- Function: Rod journals are where the big ends of the connecting rods attach. They are also known as crank pins and connect to the main journals via the crankshaft webs.
- Design: The rod journals have a cylindrical shape that allows them to rotate with the big end of the connecting rod. These are often paired with plain rod bearings, though in some cases, bushings or roller bearings may be used.
- Connection: Rod journals are linked to the main journals by crankshaft webs. The distance from the center of the main journal to the center of the rod journal is called the crank throw, which determines the engine’s stroke.
- Lubrication: Oil travels inside the crankshaft, through the main journal, diagonally through the web, and out the rod journals to lubricate the rod bearings.
Functions and Importance of Crankshaft Journals
Crankshaft journals are important for the smooth operation of an engine. They support the crankshaft and allow it to rotate efficiently. These journals are designed to reduce friction and wear with the help of bearings.
Main Journals
- Rotation and Support: Main journals rotate within the engine block’s main bearings, held in place by main bearing caps. This rotation is crucial for the crankshaft’s function and the engine’s overall performance.
- Axis of Rotation: Main journals define the crankshaft’s axis of rotation, keeping it stable and aligned within the engine block.
- Smooth Rotation: Bearings support the main journals, reducing friction and wear, and allowing the crankshaft to rotate smoothly.
Rod Journals (Crankpins)
- Connecting Crankshaft and Connecting Rods: Rod journals, or crankpins, link the crankshaft to the connecting rods of each cylinder. In a V-engine, one crankpin may serve two cylinders.
- Rotary Motion Conversion: These journals convert the pistons’ linear motion into rotary motion through the connecting rods. The crank throw, or radius, determines the engine’s stroke, which is always twice the crank throw.
- Bearings for Smooth Operation: Rod journals rotate with the “big end” of the connecting rods, assisted by rod bearings. These bearings may be plain bearings, bushings, or roller bearings, depending on the engine’s design.
Key Factors in Crankshaft Journal Function
- Crank Throw: The crank throw is the distance between the centerlines of the main journal and the rod journal. It is important for determining the engine’s stroke.
- Materials and Durability: Crankshafts and their journals are made from forged steel with hardened surfaces and strong cores to handle heavy loads and high torsion.
Crankshaft journals are essential for engine efficiency, performance, and longevity.
Design and Construction
The crankshaft journal is an essential part of the engine’s crankshaft. It must withstand the high forces during engine operation. The design of crankshaft journals emphasizes durability, wear resistance, and high performance.
Materials Used in Crankshaft Journals
Crankshaft journals are made from: – Forged steel – Alloyed heat-treated steel – Nitrided steel
These materials are chosen for their: – Hard surface that resists wear – Tough core for increased strength and durability
Common alloying elements include manganese, chromium, molybdenum, nickel, and silicon. These elements improve hardness, tensile strength, and impact resistance.
Surface Hardening Methods
Crankshaft journals are surface-hardened to improve wear resistance. Common methods are: – Induction Hardening: This process hardens the bearing locations and rounded zones, creating a thick layer for wear resistance without affecting the rest of the crankshaft. – Nitriding: This method exposes the crankshaft to ammonia, forming nitrides on the surface. It enhances rigidity and wear resistance, followed by reheating and quenching to further increase hardness.
Crankshaft Manufacturing Methods
Crankshafts can be made using different manufacturing processes: – Casting: Less common for high-performance crankshafts, casting is used for built-up crankshafts and is efficient for mass production. – Forging: This method results in higher fatigue strength, especially with the RR (TR) forging technique, where critical areas like fillets are reinforced for durability. – CNC Machining: This method offers design flexibility, making it ideal for high-performance applications. CNC machining includes lathe shaping, milling, polishing, and dynamic balance adjustments.
Crankshaft Journal Treatment Process
- Shaping on the lathe: This process shaves the journals, leaving space for finishing.
- Milling the pin and weight: This step coarsely shaves the weight and pin areas.
- Conditioning quality and shot peening: This process removes internal stress, stabilizes the structure, and sets the hardness.
- Polishing the journals and crank pins: Final polishing ensures smooth surfaces.
- Dynamic balance adjustment: This step ensures the crankshaft is balanced to reduce oscillation.
Role in Engine Operation
The crankshaft journal is crucial in engine operation. It converts the pistons’ linear motion into rotational motion, which is necessary to power the vehicle. When fuel burns in the engine’s cylinders, it creates pressure that forces the pistons down, generating linear motion. The connecting rods attached to the pistons pivot as the pistons move, causing the crankshaft to rotate. This rotation drives the wheels and moves the vehicle forward.
Distribution of Loads
Crankshaft journals are designed to handle different loads generated by the engine, like bending and twisting stresses. To manage these forces, counterweights are attached to the crankshaft webs. These counterweights are balanced against each rod journal to ensure smooth engine operation. The counterweight mass is calculated based on the weight of the piston and rod, reducing strain on the main Crankshaft bearing journals.
Lubrication and Oil Flow
Crankshaft journals have oiling holes and passageways to supply lubricant. These passageways run through the crankshaft, from the main journal, through the web, and to the rod journals. The lubrication system creates a fluid-film barrier between the crank journals and the rod and main bearings. The oil layer prevents metal-to-metal contact, reducing wear and increasing engine life. Centrifugal force pushes the oil through the passageways, and the journal’s rotational movement creates a high-pressure oil wedge, keeping the journal and bearing separated.
Key Components Related to Crankshaft Journals
- Main Bearing Journals: These are the main rotating axis of the crankshaft, secured to the engine block. They are machined for precision and usually hardened for durability.
- Connecting Rod Journals: Located at the ends of the connecting rods, these journals need oil passageways for lubrication due to their rotating motion.
- Counterweights: Positioned opposite each rod journal, counterweights balance the piston/rod assembly to maintain smooth rotation.
- Oil Passageways: These channels ensure continuous lubrication by delivering oil to the rod journals, reducing friction and heat buildup.
Additional Components and Features
The crankshaft is made up of more than just journals. It includes several important parts that affect its function and performance in the engine.
Crank Webs
Crank webs link the crank pins (or throws) to the main journals. This gives the crankshaft its strength. They are key to evenly distributing the forces from the pistons and connecting rods across the crankshaft. This helps the crankshaft stay durable and handle high-pressure conditions in the engine.
Counterweights
Counterweights are attached to the crank webs. They help balance the forces and masses created by the piston, piston pin, and Connecting Rod. They reduce the imbalance caused by the pistons’ motion. This helps by: – Reducing engine vibrations – Smoothing engine performance – Extending the lifespan of engine parts by ensuring even force distribution
Flywheel Mounting Flange
The flywheel mounting flange connects the crankshaft to the flywheel. It is usually larger than other parts of the crankshaft to create a strong attachment point for the flywheel. The flywheel helps smooth the power output from the engine by storing rotational energy.
Crankshaft Pulley
At the opposite end of the crankshaft from the flywheel, the crankshaft pulley powers engine accessories such as the alternator, power steering pump, and air conditioning compressor. It also usually has a harmonic balancer to manage engine pulses and vibrations. This ensures that rotational forces are properly distributed to the accessories, improving engine performance.
Crankshaft journals are crucial for an engine’s smooth operation and long life. Their design, lubrication, and durability are essential for any vehicle’s performance. I believe that knowing how they work helps us appreciate the details behind every engine’s power and accuracy. With proper maintenance, these small but powerful parts can ensure a vehicle runs efficiently and reliably for many years.