How Do You Repair A Crankshaft?

Steps in Crankshaft Repair

Crankshaft repair involves several stages to restore its function and prevent further damage. These steps are crucial for making sure the crankshaft works well after the repair.

1. Fault Detection and Failure Assessment

The first step in crankshaft repair is identifying the root cause of the damage. This includes testing to assess the severity and find the faulty parts. A complete inspection helps determine the exact issue, guiding the repair process and ensuring an accurate repair plan.

2. Crankshaft Grinding

Once the issue is identified, the next step is to grind the crankshaft with specialized machinery. This process removes wear or damage, restoring the crankshaft’s size and ensuring smooth performance. Grinding is essential for improving the crankshaft’s function and efficiency.

3. Superfinishing for Surface Flatness

To ensure the crankshaft surface is perfectly flat, a superfinishing machine is used. The machine uses a carborundum stone that moves quickly to smooth the surface. Superfinishing happens after the initial machining and ensures a high-quality surface.

According to the SAE J1086 standard, the surface roughness of a crankshaft should reach 15 micro-inch Ra or better. This ensures that the crankshaft performs efficiently with minimal friction. For high-performance engines, such as those used in racing or heavy-duty applications, the surface finish must reach 10 micro-inch Ra to guarantee optimal operation and extended service life.

Customer Feedback:
“The crankshaft repair service provided by Volgen Power is extremely professional. The repaired crankshaft is as smooth as a new one. The effect is remarkable.”
This feedback highlights the precision and quality of Volgen Power’s crankshaft repair services, ensuring that every repair meets the necessary surface finish standards for enhanced engine performance.

4. Polishing for Precision

Polishing is key for achieving the correct shape and surface finish. This step helps ensure the crankshaft meets the needed precision and smoothness for efficient operation. It’s an important part of the repair process.

5. Heat Treatment (if needed)

If the failure assessment shows heat-related hardness, heat treatment may be necessary. The crankshaft is heated, soaked, and cooled, usually using ceramic blankets in an annealing process. Heat treatment reduces hardness and restores the crankshaft’s strength.

6. Peen Straightening (if needed)

If the crankshaft is bent due to stress, peen straightening may be required. This process involves using a peening hammer to strike the crankshaft’s journal, relieving stress and restoring its original shape.

7. Additional Services

• Grinding: Removes wear and damage from the crankshaft.
• Dressing: Restores the surface quality of the crankshaft.
• Polishing: Achieves the correct shape and surface finish.
• Crankshaft Pulley Repair: Repairs or replaces the crankshaft pulley.
• Canal Cleaning: Cleans the oil passages in the crankshaft.
• Connecting Rod Bearing Replacement: Replace the bearings on the connecting rods.
• Crankshaft Balancing: Balances the crankshaft to prevent vibrations and uneven wear.

Under high load or special application scenarios, the use of laser coating technology to repair the crankshaft surface can effectively improve its wear resistance and extend its service life.

8. Considerations for Crankshaft Repair

Cost of Crankshaft Repair vs. Replacement

The success of the repair depends on several factors: – The extent of the damage, such as cracks or wear on the journals. – The need for specialized equipment and professional expertise. – The cost and difficulty of dismantling the crankshaft for inspection and repair.

• Polishing: A simple polishing of all journals for a four-cylinder engine can cost as low as $100.
• Major Repairs: A comprehensive repair involving welding, grinding, stress relieving, balancing, and testing can range from several hundred dollars to over $1,000, depending on factors such as location and vehicle model.
• Specialized Services: In-situ grinding or onboard annealing may incur additional costs but can be more cost-effective in terms of labor since they reduce downtime by allowing repairs without removing the crankshaft from the engine block.

It’s important to note that the total cost can vary significantly based on:

• The extent of damage (e.g., minor wear vs. major cracks).
• Whether the crankshaft needs to be removed from the engine.
• The specific steel alloy used in the crankshaft, may affect repair viability and cost-effectiveness.

Repair Time Estimates

Timeframes for each step in the crankshaft repair process can also influence decisions, particularly for those concerned about vehicle downtime:

• Crankshaft Grinding: This process typically takes several hours, depending on the severity of wear and the specific machinery used.
• Polishing: Polishing may take an additional few hours after grinding to ensure precision.
• Heat Treatment (Annealing): This could take several hours, including the heating and cooling phases.
• In-Situ Grinding: For large engines, this method can significantly reduce downtime compared to traditional methods, potentially saving several days.

9. Cracks and Failure Modes

If cracks are found, the depth of the crack about the journal diameter is critical. Cracks deeper than a quarter inch may make repair impossible. Visual inspections and Magnaflux testing help assess the cracks. Fatigue failure, often caused by cyclical loads, is common in crankshafts, and accurately predicting its lifespan is key to preventing future failures.

Real-Life Examples of Successful Repairs

1. Goltens Onboard Annealing: Goltens successfully repaired nearly 200 damaged crankshafts globally using onboard annealing techniques. This method allowed them to avoid crankshaft replacements, significantly reducing downtime for vessels. For instance, a large marine engine had its crankshaft restored without removal, showcasing the efficiency of this specialized repair method.
2. MAN PrimeServ In-Situ Repair: MAN PrimeServ utilized in-situ annealing on a 7L58/64CD engine, effectively restoring the crankpin’s hardness while maintaining its original diameter. This not only saved costs but also minimized the time the engine was out of service, demonstrating how in-situ techniques can be advantageous for large industrial engines.
3. Case Study of a Four-Cylinder Diesel Engine: A four-cylinder diesel engine’s crankshaft suffered from premature breakage due to overload. After a thorough assessment and subsequent repair involving grinding and polishing, the crankshaft was restored to operational condition. The manufacturer implemented design changes based on failure analysis, which has since prevented further fractures.

Before-and-After Data

• Crankshaft Tolerance Improvement: After grinding a worn crankshaft, tolerance improved from an initial measurement of 
  0.015

  $0.015$ inches to  0.002

  $0.002$ inches, demonstrating a significant enhancement in precision.

• Surface Roughness Improvement: The surface roughness of a crankshaft journal was measured at 
  32

  $32$ microinches Ra before polishing. After the polishing process, it was improved to  10

  $10$ microinches Ra, indicating a much smoother finish conducive to better lubrication and reduced wear.

• Wear Reduction: A crankshaft that underwent repair showed a reduction in wear from 
  0.020

  $0.020$ inches to  0.005

  $0.005$ inches after the grinding and polishing processes were completed, highlighting the effectiveness of these repairs in extending the lifespan of engine components.

Specialized Techniques

Repairing a crankshaft effectively is crucial for restoring its function while reducing material loss and downtime. One of the best methods is annealing, a heat treatment process that improves the crankshaft’s flexibility and lowers the hardness caused by issues like bearing failures.

Key Steps in the Annealing Process

• Annealing Heat Treatment: The crankshaft is heated to a specific temperature (up to 630°C) using ceramic heating blankets. This helps the steel molecules change and return the metal to its original flexibility, relieving stress.
• Removal of Components: Before heating, essential parts like the main bearings and flywheel are removed to prevent damage during treatment.
• Temperature Monitoring: Ceramic tiles and thermocouples are used to keep track of the temperature, ensuring that heating and cooling are even.

Benefits of Annealing

• Reduced Hardness: Annealing softens the crankshaft, making it less likely to crack or break.
• Minimal Material Removal: The process removes very little material, keeping the crankpin’s original size and avoiding the need for special parts like smaller bearings or connecting rods.
• Cost-Effective: Compared to replacing the crankshaft, annealing is much cheaper. For example, a repair by MAN PrimeServ only took six weeks, while a replacement would have meant longer downtime and higher costs.

Real-World Applications

• Onboard Annealing: Goltens has successfully repaired nearly 200 damaged crankshafts worldwide using onboard annealing. This avoided replacements and greatly cut downtime.
• In-Situ Repair: MAN PrimeServ used in-situ annealing to repair a 7L58/64CD engine. This restored the crankpin’s hardness without reducing its diameter, showing the precision and efficiency of this method.

These techniques are crucial for durable crankshaft repairs while offering major savings in both time and cost.

Inspection and Testing

When repairing a crankshaft, it’s important to inspect and test thoroughly to find any cracks or defects that could affect engine performance. The most common method for this inspection is magnetic particle testing (Magnaflux). This method helps identify flaws on or near the surface.

Preparing the Crankshaft for Inspection

• Cleanliness: Before starting the inspection, make sure the crankshaft is clean and dry. Remove all carbon, oil, and grease to reveal the bare metal. This ensures accurate results.

Magnetization Process

• Magnetization: The crankshaft must be magnetized in two perpendicular directions. This helps detect both longitudinal and transverse flaws. A circular magnetic field identifies longitudinal flaws, while a longitudinal magnetic field detects transverse ones.
• Current Calculation: Use the ASTM formula to calculate the headshot current:
  Head Shot Current = 20 X Diameter(mm)
  (where the diameter is double the lobe’s diameter).

Testing Procedure

• Place the crankshaft on steady rollers and apply a magnetic solution bath.
• Press the ‘Cycle Start’ button to begin the test, then clamp the crankshaft and position the coils.
• Stop the magnetic solution flow and pass the current through the crankshaft in multiple directions.
• Monitor the test with a digital metering unit.
• After the test, inspect the crankshaft under UV light to find cracks or defects. Rotate the crankshaft on the rollers to check it completely.

Detection Mechanism

The magnetic particles in the solution create visible lines over any cracks when the crankshaft is magnetized. These lines, seen under UV light, help pinpoint flaws. Cracks create a north and south pole on either side, attracting fine iron powder and highlighting the problem areas.

Use of Yoke or Coils for Manual Testing

For manual inspections, you can use a yoke (an electric magnet). The yoke generates a strong magnetic field, making the iron powder show cracks. This is an alternative to machine-based testing.

Tools and Equipment

Repairing a crankshaft requires the right tools to ensure accuracy and speed. Here are the essential tools:

Crankshaft Harmonic Damper Pulley Holding Tool

This tool is necessary to keep the crankshaft aligned while removing or installing damper bolts. A good example is the STEELMAN 42021, which is made for Honda and Acura engines. It is built from strong steel to handle the pressure of breaking tough crankshaft bolts.

• Material: Strong steel for durability.
• Drive Size: Works with a 1/2-inch drive breaker bar.
• Design: Made specifically for Honda and Acura engines.
• Dimensions: 4 in. L x 1.95 in. W x 1.95 in. H weighs 1.28 lbs.

Crankshaft Disassembly Tool

This tool is used to quickly break down the crankshaft in a hydraulic press. It’s made from durable billet steel with a corrosion-resistant zinc coating and works with most single and twin-cylinder motorcycle crankshafts.

Crankshaft Turning Socket

This tool is used to turn the crankshaft during assembly or maintenance and. fits various engine types. For example, the Sunex Crankshaft Turning Socket works with a small block Ford, Pontiac, and Buick V8 engines and uses a 1/2-inch drive.

Harmonic Balancer Pullers

These tools are crucial for safely removing the harmonic balancer from the crankshaft. Without the right pullers, it can be a tough job.

Crankshaft Position Sensor Tools

These tools adjust and test the crankshaft position sensor to ensure correct engine timing and performance.

Rotation Adapters

These adapters help rotate the crankshaft during different repair or maintenance stages, keeping everything properly aligned.

FAQs.

Q: How do I know if my crankshaft needs to be replaced?
A: If the crankshaft has deep cracks, significant wear, or deformation that can’t be repaired, it likely needs replacement. Cracks deeper than 0.25 inches or structural damage are key indicators.

Q: What are the signs of a damaged crankshaft?
A: Symptoms include unusual engine vibrations, oil leaks, poor engine performance, and metal debris in the oil filter.

Q: How much does crankshaft repair cost on average?
A: Crankshaft repair typically costs between $500 and $1,500 for basic repairs, and up to $2,000 or more for advanced treatments, depending on the severity.

Q: Can crankshafts be repaired multiple times?
A: Yes, crankshafts can be repaired multiple times, but there’s a limit to how much material can be removed. Extensive repairs may require replacement.