How to Polish Crankshaft Journals

To polish crankshaft journals, start by cleaning the journals thoroughly and inspecting them for damage. Use a crankshaft polishing tool with abrasive belts, beginning with a coarser grit to remove imperfections, and progressively switch to finer grits for a smooth finish. Ensure to apply even pressure and check the progress frequently to avoid over-polishing.

Polishing crankshaft journals is a crucial process in engine maintenance and repair that ensures smooth operation, reduces friction, and prolongs the engine’s life. The crankshaft journals, which connect with engine bearings, must be smooth and free of imperfections to prevent wear and maintain performance. Polishing is essential whenever you notice scratches, grooves, or minor damage on the crankshaft journals, or during an engine rebuild.

Why Polishing Crankshaft Journals is Important

A well-polished crankshaft not only enhances oil flow and reduces heat buildup but also helps protect engine components, ultimately improving overall performance and reliability.

1. Reduces Friction and Wear: A polished crankshaft journal provides a smooth surface that minimizes friction between the crankshaft and the engine bearings, reducing wear on both components.
2. Prevents Bearing Damage: A smooth journal surface prevents excessive heat buildup and wear, protecting the bearings from damage and extending their lifespan.
3. Improves Oil Flow: Polished journals help maintain a consistent oil film between the journal and the bearing, ensuring proper lubrication and cooling during engine operation.
4. Enhances Engine Performance: Reducing friction and wear leads to a more efficient engine, with better fuel economy, smoother operation, and potentially increased power output.

How to Polish Crankshaft Journals

Before you start polishing crankshaft journals, you’ll need to gather the following tools and materials:

1. Crankshaft Polishing Tool: A handheld or machine-driven tool specifically designed for polishing crankshaft journals. This tool is fitted with abrasive belts or strips.
2. Abrasive Belts or Strips: Polishing belts of various grits (typically ranging from 120 to 600 grit) are used to remove material from the journal surface progressively.
3. Degreaser or Solvent: To clean the crankshaft journals thoroughly before polishing.
4. Clean Rags or Cloths: For wiping down the crankshaft and removing debris or oil.
5. Micrometer or Dial Gauge: To measure journal dimensions and check for roundness and taper.
6. Protective Gear: Safety glasses, gloves, and a dust mask to protect against metal particles and debris.
7. Polishing Lubricant (Optional): Some polishing processes may require a light lubricant to reduce friction and heat during polishing.

Polishing Crankshaft Journals – Step-by-Step

Follow the step by step guide below to polish crankshaft journal easily and successfully –

1. Inspect the Crankshaft

Before starting the polishing process, carefully inspect the crankshaft for any visible signs of damage, such as deep grooves, cracks, or heavy scoring. Check the journals for roundness and taper using a micrometer or dial gauge. If there is significant damage or out-of-roundness, the crankshaft may need to be machined or replaced rather than polished.

2. Clean the Journals

Thoroughly clean the crankshaft journals using a degreaser or solvent to remove any oil, grease, dirt, or debris. Ensure that the journals are completely dry before starting the polishing process. Cleaning is crucial because any contaminants left on the surface can interfere with the polishing and cause additional damage.

3. Choose the Right Abrasive Belt or Strip

Select an appropriate abrasive belt or strip based on the condition of the journal surface. For heavily scratched or damaged surfaces, start with a coarser grit (such as 120 or 180) to remove imperfections. Gradually move to finer grits (such as 400 or 600) to achieve a smooth, polished finish.

4. Set Up the Polishing Tool

Depending on the type of polishing tool you are using, install the abrasive belt or strip onto the tool as per the manufacturer’s instructions. For machine-driven tools, secure the crankshaft in the polishing machine, ensuring that it is properly aligned and balanced. Adjust the speed settings and tension of the abrasive belt to ensure a consistent and even polish.

5. Begin Polishing the Journals

• Manual Polishing: If using a handheld tool, wrap the abrasive strip around the journal and apply even pressure while moving the tool back and forth along the length of the journal. Keep the crankshaft rotating slowly to ensure an even finish on all sides.
• Machine-Driven Polishing: For machine-driven polishing, start the machine at a low speed and gradually increase to the recommended speed. Gently apply the abrasive belt to the journal surface with consistent pressure. Let the crankshaft rotate while the belt polishes the journal, moving the tool back and forth to ensure an even finish.

6. Check the Progress Frequently

Stop periodically to inspect the journal surface and check the progress of the polishing. Look for a uniform, smooth finish without visible scratches or marks. Use a micrometer to check for any changes in diameter and ensure the journal remains within specification. Adjust the pressure and speed settings as needed to achieve the desired finish.

7. Change to Finer Grit Abrasives

Once the major imperfections have been removed, switch to a finer grit abrasive belt or strip. Continue polishing to remove any remaining scratches or marks and achieve a smoother finish. Repeat the process as needed, using progressively finer grits until the journals have a mirror-like finish.

8. Final Inspection and Cleaning

After polishing, conduct a final inspection to ensure the crankshaft journals are free of imperfections and meet the required specifications. Measure the journal diameter and roundness to confirm accuracy. Clean the crankshaft thoroughly with a solvent or degreaser to remove any abrasive particles or debris.

9. Protect the Journals

Once polishing is complete, apply a light coat of protective oil to the crankshaft journals to prevent rust and corrosion. Store the crankshaft in a clean, dry environment until it is ready for reassembly.

Tips for Effective Crankshaft Journal Polishing

Here are some effective tips for the polishing –

• Use Proper Safety Equipment: Always wear safety glasses, gloves, and a dust mask to protect against metal particles and abrasive debris.
• Avoid Over-Polishing: Excessive polishing can remove too much material, resulting in improper journal diameter and bearing clearance. Polish only until the surface is smooth and free of imperfections.
• Maintain Consistent Pressure: Apply even pressure throughout the polishing process to avoid creating low spots or uneven surfaces on the journal.
• Check Abrasive Condition Regularly: Replace abrasive belts or strips as needed to maintain their effectiveness and prevent damage to the crankshaft.
• Ensure Proper Alignment: When using a machine-driven tool, make sure the crankshaft is correctly aligned and balanced to prevent vibration or damage during polishing.

Frequently Asked Questions

Here are some FAQs about the polishing crankshaft journals –

1. What is the best grit for polishing crankshaft journals?
   Start with a coarser grit, such as 120 or 180, to remove deep scratches or imperfections. Progress to finer grits, like 400 or 600, for a smooth, mirror-like finish. The choice of grit depends on the condition of the journal surface.
2. Can I polish crankshaft journals by hand?
   Yes, you can polish crankshaft journals by hand using a handheld polishing tool and abrasive strips. However, machine-driven polishing tools provide more consistent results, especially for larger crankshafts or when precision is critical.
3. How often should I polish crankshaft journals?
   Polishing should be done whenever there are visible signs of wear or damage on the crankshaft journals or during an engine rebuild. Routine inspection can help determine when polishing is necessary.
4. Is polishing the crankshaft journals always necessary?
   Polishing is necessary when journals have minor scratches, wear marks, or imperfections that can affect engine performance. If the journals are in good condition with no visible damage, polishing may not be required.
5. Can polishing fix all crankshaft journal issues?
   Polishing can remove minor wear, scratches, and surface imperfections, but it cannot repair deep cracks, severe scoring, or structural damage. Significant defects may require machining or replacing the crankshaft.

Conclusion

Polishing crankshaft journals is a vital step in engine maintenance and repair that helps ensure smooth operation, reduces friction, and extends the life of both the crankshaft and bearings. By following the correct steps and using the appropriate tools and abrasives, you can achieve a polished finish that enhances engine performance and reliability. Regular inspection and proper polishing techniques will keep your engine running smoothly and efficiently for years to come.