How To Fix A Crankshaft With Minimal Damage?

Initial Inspection and Diagnosis

The first step in fixing a Crankshaft with minimal damage is to inspect and diagnose it properly. This helps assess its condition and identify any problems that need attention.

Visual Inspection for Crankshaft Defects

Check for cracks, fractures, wear, and weakness. Begin by looking at the crankshaft for any visible defects, such as cracks, scoring, discoloration, or signs of overheating. These could point to areas that need further examination.

Non-Destructive Testing (NDT) for Hidden Damage

Ultrasound, magnetic particles, and dye penetrant methods are useful for detecting hidden defects.

• • Dye penetrant inspection: This method uses a dye that seeps into cracks or gaps, making them visible.
  • Magnetic particle inspection: This technique finds surface and subsurface fractures by magnetizing the crankshaft and spraying magnetic powder on areas that might have cracks. The powder collects at crack sites, showing their location and severity.
  • Ultrasonic testing: This method finds deeper issues, like internal cracks or hollows, which are invisible to the eye.

Crankshaft Cleaning

Clean the crankshaft to remove dirt, oil, or contaminants. Proper cleaning is essential for a precise inspection. Techniques like ultrasonic cleaning can remove tough contaminants, while chemical degreasing is needed for heavy oil and dirt buildup.

Measurement of Crankshaft Dimensions

Measure journal diameters, bearing clearances, and web thicknesses using precision tools. Compare these measurements to the manufacturer’s specifications to check for wear or damage.

• • Main journal diameter: Use a micrometer to measure the diameter at the center of each main journal. Make sure these measurements match the engine’s requirements.
  • Rod journal diameter: Measure the rod journals in several places and check for taper or ovality. Ensure they are within the acceptable tolerance range.

Runout Measurement

Measure journal runout using a dial indicator. Support the crankshaft on V-blocks and look for any irregularities. The maximum allowable runout depends on the engine type:

• • For inline engines, the runout should not exceed 0.002 inches.
  • For V-type engines, the runout is usually 0.002 inches for journals near the support points and 0.004 inches for those in the middle.

Thread and Oil Feed Hole Inspection

Inspect threaded holes: Make sure all threaded holes are clean and undamaged. You can use a chaser tap to clean the threads without removing too much material.

Inspect oil feed holes: Ensure the oil feed holes for the main and rod journals are clear of debris. Remove any sharp edges and make sure the oil can flow properly.

By following these steps, you can accurately assess the crankshaft’s condition and identify any necessary repairs, helping to restore its function with minimal damage.

Dismantling the Engine

To dismantle the engine for crankshaft repair with minimal damage, follow these key steps:

• Lock the Engine to a Stable Surface
  Secure the engine on a stable surface to prevent movement. This helps reduce the risk of damaging parts during disassembly and keeps the workspace safe.
• Gather Necessary Tools and Equipment Collect all the required tools and safety Gear before starting. Make sure your working area is clean to prevent dirt or dust from contaminating the engine components.
• Remove the Front Housing and Flywheel Housing
  Follow the disassembly instructions to remove these parts. This step is crucial to access the crankshaft and other internal components.
• Remove the Engine Head, Pistons, and Connecting Rods Carefully disassemble these components to reach the crankshaft. Store all removed parts in a clean, organized way to keep them in good condition for reassembly.
• Remove the Main Bearing Caps
  Remove the main bearing caps carefully. Note their location and orientation. Mark them to ensure they are reinstalled correctly during reassembly.

Key Tools for Dismantling

Lifting Device: You’ll need a lifting device to safely lift the crankshaft (approximately 159 kg or 350 lb) from the cylinder block without causing damage.

Specialized Tooling: Use bearing pullers, step plates, hand hydraulic pumps, push-puller legs, and puller plates to safely remove components.

Contaminant Management: Make sure all parts are free from contaminants to avoid wear. Have containers ready to collect fluids before opening compartments or disassembling parts. Dispose of fluids according to local regulations.

By following these steps, you can minimize damage and prepare the engine for a smooth crankshaft repair.

Removing Damage

To fix a damaged crankshaft, there are a few steps involved, depending on the type and severity of the damage.

Crankshaft Grinding and Polishing

If the crankshaft surface shows wear, cracks, or warping, grinding is the first step. A special machine is used to grind the crankshaft diameter, removing a small layer of metal. This restores the crankshaft’s original shape and size, improving its performance. After grinding, the crankshaft is polished to make the surface smoother and shinier, reducing friction and ensuring better operation.

Straightening Bent Crankshafts

If the crankshaft is bent or misaligned, straightening is necessary. A hydraulic press applies heat and pressure to correct any bending or misalignment. When done properly, this step ensures the crankshaft rotates smoothly in the engine, without causing extra wear or damage.

Peen Straightening to Reduce Stress

Sometimes, stress-induced bends need attention to restore the crankshaft to its original shape. Peen straightening involves striking the crankshaft’s journal with a peening hammer to reduce stress and straighten it. This method helps relieve strain without compromising the crankshaft’s integrity.

Welding for Cracks or Breaks

For severe damage like cracks or breaks, welding is an option. The broken pieces of the crankshaft are welded together using a welding machine. After welding, the crankshaft is re-grounded to ensure it meets the original specifications.

Heat Treatment for Hardness

Heat treatment can sometimes be needed to reduce hardness caused by heat. This process involves controlled heating, soaking, and cooling of the crankshaft, often using ceramic blankets in an annealing process. This treatment ensures the crankshaft is not too brittle and maintains its strength for long-term durability.

Costs Involved

The costs for these procedures can vary: – Crank grinding/polishing: $500 – $1000+ – Straightening bent crank: $300 – $600 – Labor for disassembly/reassembly: 5-20 hours x shop rate

Tools Required

• Superfinishing machine: Ensures flatness of the crankshaft surface using a carborundum stone.
• Specialist machines: Used for grinding and machining the crankshaft diameter.
• Hydraulic press: Used for straightening the crankshaft.
• Peening hammer: Reduces stress-induced bends.
• Welding machine: Repairs cracks or breaks in the crankshaft.

Grinding and Polishing

Grinding and polishing are crucial steps in repairing a crankshaft with minimal damage. These processes need precision to create a smooth surface and prevent further damage.

Grinding Process

Grinding Direction: Grind opposite the engine’s rotation. This technique creates a surface that reduces wear on the bearing surfaces during operation.

Abrasive Tools: Use abrasive wheels to remove material and prepare the crankshaft for polishing.

Polishing Process

Polishing Direction: Always polish in the engine’s rotation direction. This smooths out rough edges from the grinding process.

Polishing Tools: Use abrasive belts or microfinishing tape. The tape method gives a more consistent surface by applying the tape against the rotating crankshaft journal.

Surface Finish

Standard Finish: Aim for surface roughness of 15 microinches Ra or better for typical crankshaft applications.

High-Performance Crankshafts: For high-performance or diesel engine crankshafts, a smoother finish of 10 microinches Ra or better is needed for optimal performance.

Additional Considerations

• Superfinishing Machines: After grinding, use a superfinishing machine with a carborundum stone to refine the surface. The stone’s oscillating motion helps achieve a fine finish.
• Nodular Cast Iron Crankshafts: These need careful polishing due to their graphite structure. Polishing in the right direction removes rough edges.
• Forged Steel Crankshafts: While these don’t require grinding and polishing in opposite directions, it’s still best to polish in the direction of the engine’s rotation for the best result.

Common Issues

Overpolishing: Avoid overpolishing, as it can create a “halo effect” around oil holes. This reduces the bearing area and oil film strength, which can lead to bearing failure.

Incorrect Orientation: Make sure the crankshaft is correctly mounted during grinding and polishing. Incorrect orientation can leave burrs that damage the bearings.

Welding and Journal Restoration

Welding and journal restoration are key steps in repairing a crankshaft with minimal damage, ensuring it performs well again.

Modern Welding Techniques

Modern welding methods, like submerged arc welding, work well for crankshaft repairs. These techniques fill cracks with the right materials, keeping the crankshaft’s power and function intact.

Heat and Stress Management

Welding creates a lot of heat, which can cause internal stresses in the crankshaft. To fix this, post-weld heat treatment or cryo treatment is needed to relieve stress and harden the crankshaft.

Weld Materials

• Small Repairs: For small repairs, materials like bronze or Eutaloy are used.
• Large Repairs: For bigger fractures, ER70-S2 or similar filler materials are recommended, especially for cast steel crankshafts.

Welding and Grinding

After welding, the crankshaft journals must be ground to their original size. Precision grinding ensures the crankshaft meets the exact specifications.

Hard Chrome Plating

Hard chrome plating is another restoration option, but it can cause risks like hydrogen embrittlement, which may lead to cracking. To avoid this, baking the plated crankshaft at 200°C for a few hours is recommended.

Metalizing

Metalizing is an alternative method for journal restoration. It requires specialized knowledge and is less commonly used than other techniques.

Tolerance Requirements

Crankshafts need precise tolerances, typically within +/-0.003 inches. Sticking to these tolerances is crucial for the crankshaft’s function and overall engine performance.

Straightness and Radius Repair

Maintaining the crankshaft’s straightness during the repair is vital. Extra care is taken to repair the radius of each journal to meet the original specifications.

Magnaflux Testing

After welding, a magnaflux test (wet fluorescent) checks for cracks or defects, especially around the journal radius and fillets.

Straightness Check

To check the crankshaft’s straightness, it should be supported by the main journals in narrow V blocks. The crankshaft must have less than 0.0010″ Total Indicator Reading (TIR) across its critical surfaces.

Cost Considerations

Repairing a crankshaft journal can be expensive—around $600 for one journal, or double that for all rod journals. The decision to repair or replace depends on the crankshaft’s value and repair cost.

Heat Treatment and Peen Straightening

Heat treatment and peen straightening are two essential techniques used to restore crankshafts with minimal damage. These processes help improve the durability, alignment, and performance of the crankshaft, avoiding the need for full replacement. Let’s take a deeper look into each method.

Heat Treatment

Heat treatment is an effective method to relieve internal stresses and correct misalignments in crankshafts. It’s particularly useful when dealing with hardness or distortion issues without compromising the part’s mechanical properties.

Process Breakdown:

Material Composition: The type of material used in the crankshaft determines the heat treatment parameters. Common materials such as cast iron or forged steel require specific temperatures, heating rates, soak times, and cooling rates. For example, forged steel crankshafts typically undergo heat treatment at temperatures between 850°C – 950°C.

Process Steps:

1. 1. Pre-Inspection: Before heat treatment, the crankshaft’s hardness and bend are thoroughly checked using hardness testing equipment and a visual inspection for any obvious defects.
   2. Heating: The crankshaft is heated using ceramic blankets or heating mats, which provide uniform heat distribution. Remote heat sensors track the temperature to ensure precision during the process.
   3. Soak & Cooling: The crankshaft is held at the specified soak temperature for a period (usually 1-2 hours) to allow for uniform heating. Afterward, the crankshaft is cooled slowly using a controlled process to prevent rapid thermal contraction.

Key Parameters:

• • Soak Temperature: The crankshaft is typically heated to a temperature slightly lower than its original tempering temperature, usually between 700°C – 800°C, to avoid altering its basic mechanical properties.
  • Hardness Reduction: Heat treatment generally reduces the hardness by approximately 200 HB (Brinell Hardness). This is essential for alleviating stress and improving alignment without making the material too brittle.

Limitations:

• • Heat treatment is not effective for crankshafts with surface cracks below the rated diameter, as these can propagate during the process.
  • Overheating the crankshaft can soften the material, reducing its tensile strength and leading to potential failure.

Benefits:

• • Heat treatment is cost-effective compared to full crankshaft replacement and can restore crankshafts relatively quickly.
  • It can be an efficient method for restoring alignment and stress levels in the crankshaft, enhancing its lifespan.

Example Data:

For example, a typical forged steel crankshaft with a 600 HP engine may experience an initial hardness of around 400 HB. After heat treatment, the hardness could be reduced to 200 – 250 HB, significantly reducing brittleness and improving fatigue resistance.

Peen Straightening

Peen straightening is a non-invasive method that involves applying mechanical force to bend or distort the crankshaft back into alignment. It is particularly useful for crankshafts that have small to moderate bends, and it doesn’t require material removal, thus preserving the crankshaft’s structural integrity.

Process Breakdown:

Method: Peen straightening is done by impacting the crankshaft’s journals with controlled force using a ball peen hammer or a specialized peening tool. The crankshaft is placed on V-blocks, and an indicator is used to detect the lowest point of the bend.

Steps:

1. 1. Find the Low Spot: Use a dial indicator to measure and identify the lowest point of the bend. This ensures that you are working on the exact spot that needs adjustment.
   2. Peening: Slowly and methodically apply peening strikes to both sides of the crankshaft’s journal at the low point, gradually working to straighten the shaft. Typically, this process is done with a ball peen hammer or, in tougher cases, a sledgehammer.
   3. Check Straightness: Continue peening until the shaft is within a tolerance of +0.0005” or -0.0005”. After each pass, re-measure the crankshaft to confirm it has returned to proper alignment.

Tools and Techniques:

• • Ball Peen Hammer: The most commonly used tool, delivering precise strikes to the crankshaft’s surface.
  • Sledgehammer: Used for tougher cases with significant bends or distortion.
  • Wooden Block: Placing the crankshaft on a hardwood block helps distribute the impact force evenly to avoid surface damage.
  • Heating: Applying heat to the area (around 300°F or higher) before peening can improve results, especially when working on tough bends. The crankshaft should be held in the bent position during cooling to reverse the bend.

Practical Case Example: A 1914 Simplex 4-cylinder 600 CI crankshaft with a 0.020″ bend was successfully straightened using the peen straightening technique. After carefully applying peening strikes, the crankshaft was restored to its original alignment, proving the effectiveness of the method for repairing historical or high-performance engine parts.

Effectiveness:

Peen straightening is particularly useful for minor to moderate bends. However, it may not be suitable for severe cracks or extensive distortions. For larger cracks, welding or other repair methods may be required.

Both heat treatment and peen straightening play crucial roles in restoring crankshafts to optimal condition, offering cost-effective solutions to repair crankshafts and avoid the high costs associated with full replacements. However, these processes require significant expertise, and improper handling can lead to deformation, cracking, or additional damage to the crankshaft.

By carefully considering the severity of the damage, selecting the appropriate method, and utilizing the right tools, these methods can help ensure long-term engine performance. Whether you’re dealing with heat treatment to alleviate stress or using peen straightening to restore alignment, these repair techniques offer a way to breathe new life into an otherwise damaged crankshaft, maximizing its functionality and durability for years to come.