Step-by-Step Rear Shock Oil Change for Bomber CR Trunnion

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The Marzocchi Bomber CR Trunnion [paid link] rear shock is a high-performance suspension component designed for aggressive riding. Keeping it in top condition requires regular maintenance, including an oil change to ensure optimal damping performance and longevity. This step-by-step guide provides detailed instructions for performing an oil change on your Bomber CR Trunnion [paid link] shock. Whether you are an experienced mechanic or a DIY enthusiast, this guide will help you maintain your rear shock with ease.

Tools Required

  • 5mm Allen wrench [paid link]
  • 6mm Allen wrench [paid link]
  • Torque wrench [paid link]
  • Oil seal driver
  • Shock oil (specific to Marzocchi recommendations)
  • Shock pump
  • Towel or clean cloth
  • Small container for oil drainage
  • Suspension grease
  • Syringe for oil refilling
  • O-ring pick
  • Small screwdriver
  • Flat surface for disassembly
  • Safety gloves

Preparing the Bomber CR Trunnion for Maintenance

Before starting the oil change, ensure you have a clean workspace, and gather all the necessary tools. The Bomber CR Trunnion should be removed from the bike to make the maintenance process easier. Start by safely detaching the shock from the frame.

  1. Use a 5mm Allen wrench to remove the shock mounting bolts from the bike frame.
  2. Gently slide the shock out from the frame, keeping it upright to prevent oil spillage.
  3. Place the shock on a clean, flat surface.

It’s essential to handle the shock carefully to avoid damaging any parts, especially the bushings and seals.

Disassembling the Bomber CR Trunnion Rear Shock

Once the shock is removed, you’ll need to carefully disassemble it to access the oil reservoir.

  1. Remove the Trunnion Bolts: Use the appropriate Allen wrench (usually a 6mm) to remove the trunnion bolts that hold the shock body together. Be cautious when separating these parts as there may be tension in the internal components.
  2. Extract the Damper Shaft: Slowly pull the damper shaft out of the shock body. It’s crucial not to damage the shaft or the internal seals during this process. Keep the damper shaft in a safe place for inspection.
  3. Remove the Air Can and Bushings: After the damper is removed, carefully slide off the air can. At this point, you should also remove the internal bushings, as they need to be cleaned and inspected for wear.

At this stage, you should have access to the internal oil chamber of the rear shock.

Draining and Cleaning the Shock Oil

The next step involves draining the old oil and cleaning the components before replacing the oil.

  1. Drain the Old Oil: Place the shock upright over a container to collect the old oil. Gently press on the air can to help expel any residual oil from the oil chamber.
  2. Clean All Components: After draining the oil, clean the shock components thoroughly using a towel or clean cloth. Remove any debris, dirt, or old grease from the seals and the shock body.
  3. Inspect Internal Parts: Before proceeding, inspect the damper shaft and internal bushings for signs of damage or excessive wear. If there are any signs of damage, replace the worn-out parts.

Proper cleaning ensures that the new oil doesn’t mix with contaminants, which could impair performance.

Refilling with Fresh Shock Oil

Once the shock components are cleaned, it’s time to refill the shock with fresh oil.

  1. Prepare the Oil: Use the recommended oil for the Bomber CR Trunnion. Marzocchi typically suggests using high-quality suspension oils, but check the shock’s manual for specific oil recommendations.
  2. Refill the Oil Reservoir: Using a syringe, carefully fill the oil reservoir in the shock body with the appropriate amount of oil. Be mindful not to overfill, as this can cause air bubbles, affecting performance.
  3. Reassemble the Shock Components: Reinstall the damper shaft and air can into the shock body, ensuring that all parts are aligned properly. Lubricate the seals with suspension grease to prevent friction and ensure smooth movement.
  4. Check for Air Bubbles: When reassembling, it’s crucial to remove any trapped air. Gently compress the shock to allow any air pockets to escape [paid link] before sealing it completely.

Ensure that the oil level is consistent with the manufacturer’s recommended specifications.

Reassembling and Reinstalling the Shock

With the oil change complete, you can begin reassembling and reinstalling the shock.

  1. Reinstall the Trunnion Mount: Carefully reassemble the shock’s trunnion mount, making sure all bolts are tightened securely.
  2. Torque Specifications: Use a torque wrench [paid link] to tighten the trunnion bolts according to the manufacturer’s specified torque values. This is essential for the shock to perform at its best and avoid any potential damage.
  3. Reattach the Shock to the Bike Frame: Align the shock with the frame’s mount points and reattach it using the mounting bolts. Tighten them to the proper torque specifications to ensure a secure fit.

After reinstallation, use a shock pump to adjust the air pressure in the shock according to your rider weight and riding preferences.

Troubleshooting Common Issues After Oil Change

After completing the oil change, you may encounter some issues that can affect your shock’s performance. Here are some common problems and how to resolve them:

  • Loss of Damping or Poor Performance: This could be caused by air bubbles in the oil. To fix this, disassemble the shock again, bleed the air, and refill the oil to the correct level.
  • Leaking Oil: If oil is leaking from the shock body or air can, check that all seals are properly installed and there are no visible cracks. If seals are damaged, replace them immediately.
  • Noise During Compression: If you hear any unusual noises when compressing the shock, check the lubrication of the damper shaft and seals. Insufficient grease can lead to friction, which may cause noise.

Regular maintenance can prevent these issues from becoming more serious.

Optimizing the Performance of the Bomber CR Trunnion

To get the best performance from your Bomber CR Trunnion shock, consider the following adjustments and optimizations:

  1. Adjust the Air Pressure: Tailor the shock’s air pressure to your riding style and weight. A proper air pressure setting is key to achieving the best balance between comfort and control.
  2. Tune the Damping: The Bomber CR Trunnion allows for various damping adjustments. Experiment with the rebound and compression settings to find the optimal balance for your riding conditions.
  3. Regular Maintenance: Performing regular oil changes, cleaning, and seal inspections will keep your shock performing at its best and extend its lifespan.

Conclusion

Performing an oil change on the Marzocchi Bomber CR Trunnion rear shock is a relatively straightforward process with the right tools and attention to detail. By following the steps outlined above, you can ensure that your shock remains in top condition, delivering exceptional performance for your rides. Regular maintenance, along with proper oil changes and adjustments, will help you get the most out of your Bomber CR Trunnion for years to come.