How To Change Motorcycle Fork Seals (Shock Oil Seal Replacement)

Introduction

This tutorial provides a comprehensive guide on how to replace the fork seals on a Honda NC750X motorcycle, specifically for models from 2013 to 2016. This process is crucial for maintaining the functionality of your motorcycle's suspension system. Follow these steps carefully to ensure a successful seal replacement.

Step 1: Prepare the Motorcycle

• Loosen the 17mm top caps on each fork by half a turn. Do not unscrew them fully yet.
• Using a 5mm Allen key, remove the mud guard.
• Remove the brake hose clamp using an 8mm socket on both sides.
• Carefully lift off the mud guard.

Step 2: Remove the Brake Caliper

• Use a 12mm socket to remove the brake caliper. Rotate the disc to align with the cutout, making it easier to slide the caliper out.
• Secure the brake caliper out of the way to avoid stress on the brake line.

Step 3: Remove the Wheel Spindle

• Remove the spindle pinch bolt with a 12mm socket.
• Using a 17mm hex socket, loosen the wheel spindle.
• Place a block of wood under the sump and use a trolley jack to ease the pressure from the front of the bike. You only need minimal pressure if the bike is on its main stand.
• Remove the spindle bolt and take out both spacers, keeping them safe.

Step 4: Detach the Shock Absorbers

• Loosen the shock pinch bolt with a 14mm socket.
• Loosen the top pinch bolt.
• Carefully slide the shock out on both sides.
• Use a 6mm Allen key to loosen the bolt on the bottom of the shock. Just loosen it half a turn while applying downward pressure.

Step 5: Remove Old Seals and Oil

• Gently remove the upper cap and pour out the old oil. Make sure to do this on a clean surface.
• Clean all parts thoroughly.
• Use a flat screwdriver to gently remove the dust seal and inner oil seal retainer.
• Unscrew the lower Allen key bolt completely to separate the shock.

Step 6: Replace Fork Seals

• Remove the inner spacer and old seal.
• Clean the bushes and use some auto sol on the shock tube—avoid abrasive materials.
• Check the shock tube for cracks or damage.

Step 7: Install New Seals

• Insert the spacer as shown.
• Use a piece of waste pipe and an exhaust clamp as a makeshift tool to install bushings and seals.
• Slide the tool over the seal, clamp it in place, and tap downwards until seated (you’ll notice a change in sound).
• Create a cone from a cut-up milk carton, smear it with grease, and slide the new seal on. Ensure correct seal orientation.
• Use the old seal on top to drive the new seal into place, ensuring it's seated properly.

Step 8: Reassemble the Shock

• Reinstall the seal retainer carefully, avoiding contact with the rubber seal.
• Install the dust cover and insert the fork piston.
• Tighten the old screw back to 20 Nm.
• Fill the shock with 10W oil, leaving a 101mm air gap (approximately 500ml for each shock).
• Work the shock up and down to remove air bubbles and recheck the air gap.

Step 9: Final Assembly

• Slide the spring, spring seat, and collar back on.
• Install the top cap, ensuring it’s flush, and reinstall the shock.
• Tighten the lower pinch bolts to 39 Nm and the top cap to 22 Nm on both sides.
• Tighten the upper pinch bolt to 22 Nm.
• Grease the wheel spindle and reinstall the wheel, tightening the axle to 74 Nm and the pinch bolt to 22 Nm.

Step 10: Complete the Installation

• Carefully reinstall the mud guard.
• Reattach the brake caliper, tightening bolts to 30 Nm.
• Remove the trolley jack and pump the front brake to settle the pads.
• Check the suspension operation and inspect for leaks.
• Clean the brake disc and surrounding areas.

Conclusion

Replacing motorcycle fork seals is a critical maintenance task that enhances performance and safety. By following these steps, you ensure your suspension system is functioning properly, which can significantly improve your riding experience. After completing the process, always check for any issues before hitting the road.