05/03/2010
Your Guide to a Smooth Ride: Changing Fork Oil on a BMW F700GS
The suspension is arguably one of the most crucial components of any motorcycle, directly impacting handling, comfort, and safety. For riders of the popular BMW F700GS, maintaining the fork oil is a key part of ensuring optimal performance. Over time, fork oil degrades, losing its lubricating and damping properties. This can lead to a harsher ride, reduced responsiveness, and potentially uneven wear on your fork internals. Fortunately, with a bit of patience and the right approach, changing the fork oil on your F700GS is a manageable task that can significantly improve your riding experience. This guide will walk you through the process, from gathering your supplies to the final reassembly.
Why Change Your Fork Oil?
Fork oil, also known as suspension fluid, is more than just a lubricant. It's a vital part of the damping system within your motorcycle's front forks. As you ride, the oil is subjected to immense pressure, heat, and shearing forces. This constant stress causes the oil to break down, leading to several undesirable effects:
- Reduced Damping: Degraded oil can't effectively control the compression and rebound of the forks, resulting in a bouncy or uncontrolled feeling.
- Increased Heat: Overworked oil can overheat, further accelerating its breakdown and potentially damaging seals.
- Contamination: Tiny metal particles from wear within the forks can contaminate the oil, acting like an abrasive paste and accelerating wear.
- Inconsistent Performance: The damping characteristics can become unpredictable, making it harder to gauge how the bike will react in different situations.
Regularly changing your fork oil, typically every 15,000 to 20,000 miles or as recommended by BMW, ensures your suspension remains responsive and provides a comfortable, controlled ride.
Gathering Your Tools and Supplies
Before you begin, ensure you have all the necessary items. Having everything ready will make the process smoother and prevent interruptions. You'll need:
- New Fork Oil: Consult your F700GS owner's manual or a reputable service manual for the correct type and viscosity. Many riders opt for a 5W or 10W fork oil, but always verify. Ensure you have enough for both legs – typically around 750ml to 800ml per fork leg, but check your specific model's requirements.
- Socket Set and Wrenches: You'll need various sizes, including sockets for the front axle pinch bolts and possibly the fork caps.
- Torque Wrench: Essential for tightening components to the correct specifications, preventing damage.
- Motorcycle Stands: A front and rear stand will lift the bike securely, allowing for easier wheel removal and fork work.
- Allen Keys: For various bolts and fasteners on the forks.
- Pliers: For cotter pins or circlips if present.
- Drain Pans or Containers: To collect the old fork oil.
- Measuring Jug or Syringe: For accurately measuring the new fork oil. A graduated cylinder is ideal.
- Funnel: To pour the new oil into the fork legs.
- Rags and Shop Towels: For cleaning up spills and parts.
- Gloves: To protect your hands from oil and grime.
- Safety Glasses: To protect your eyes.
- Optional: Seal Driver: If you plan on replacing fork seals simultaneously.
Step-by-Step Fork Oil Change Procedure
This is a detailed breakdown of how to change the fork oil on your BMW F700GS. Remember, safety first; ensure the motorcycle is stable on its stands before commencing work.
1. Prepare the Motorcycle
Begin by lifting the motorcycle securely using your front and rear stands. This will allow the front wheel to hang freely. Loosen the pinch bolts on the front axle and the bolts securing the front wheel. You may also need to loosen the bolts holding the brake calipers to the fork legs. Gently remove the front wheel and set it aside.
2. Access the Fork Caps
With the wheel removed, you can now focus on the forks. Locate the fork caps at the top of each fork leg. These are typically held in place by a spring preload mechanism or are simply threaded on. You may need a specific tool or a large socket to loosen them. It's often easier to loosen the fork caps while the forks are still slightly compressed by the triple clamps, but be careful not to fully remove them yet.
3. Drain the Old Fork Oil
The most straightforward method to drain the old oil is to fully extend the fork leg and then carefully unscrew the fork cap completely. Once the cap and any associated springs or spacers are removed, invert the fork leg over your drain pan. You may need to cycle the fork leg up and down a few times to help push out as much of the old oil as possible. Some forks have a drain screw at the bottom of the fork leg, but the F700GS typically requires removal of the cap and inversion.
Important Note on Air Gaps: The concept of an 'air gap' is crucial for proper suspension function. The air gap is the space left at the top of the fork leg once the oil is drained and the fork is fully compressed (with the spring removed and internal components in their 'at rest' position). This air compresses during the last third of the fork's travel, acting as a pneumatic spring. A common measurement for the air gap is taken from the top of the fork's outer leg down to the surface of the oil. While precise measurements can be complex, a general guideline for many bikes is around 100-150mm. However, the F700GS might have specific requirements. Some riders have found that a larger air gap (meaning less oil) can reduce mid-stroke harshness. If you're unsure, start with the manufacturer's recommended oil level or a measurement derived from the service manual. If your forks came with inconsistent factory air gaps (e.g., 150mm in one leg and 110mm in the other, as reported by some riders), it's generally advisable to aim for consistency between the two legs. A gap of around 130-140mm might be a good starting point before you risk bottoming out too easily.
4. Clean and Inspect
While the oil is draining, take the opportunity to clean the exterior of the fork legs. Inspect the fork seals for any signs of leakage or damage. If you notice any oil weeping from the seals, it would be an opportune time to replace them. Also, check the fork stanchions (the shiny inner tubes) for any nicks, scratches, or pitting, which can damage the seals and lead to leaks.
5. Refill with New Fork Oil
Once the old oil has been thoroughly drained, you can begin refilling the fork legs. Use your measuring jug or syringe to accurately measure the correct amount of new fork oil. Pour the oil slowly into the fork leg using a funnel. It's recommended to add the oil in small increments (e.g., 5ml at a time) and allow it to settle. This helps to prevent air bubbles from being trapped within the oil.
Reassembly Tip: When reassembling, after adding the oil, you can gently pump the fork leg a few times to help distribute the oil. Ensure the damping rod is correctly positioned and that the spring is installed properly. Reattach the fork cap and tighten it to the manufacturer's specified torque. It’s crucial to ensure that both fork legs have the exact same amount of oil and the same air gap for consistent handling.
6. Reassemble the Forks and Wheel
With the new oil in place and the fork caps secured, you can begin reassembling the front end. Carefully slide the forks back into the triple clamps and loosely tighten the pinch bolts. Reinstall the front wheel, ensuring it's properly aligned. Tighten the front axle pinch bolts and the axle itself to the manufacturer's specified torque. Reattach the brake calipers and tighten their bolts. Double-check all fasteners to ensure they are secure.
7. Final Checks
Once everything is reassembled, slowly lower the motorcycle off the stands. Bounce the front end of the bike a few times to allow the suspension to settle. Check for any leaks around the fork seals or caps. Take the bike for a short, slow test ride in a safe area to get a feel for the new suspension performance. Listen for any unusual noises and observe how the bike handles.
Common Pitfalls and Troubleshooting
Even with careful work, issues can arise. Here are some common problems and how to address them:
| Problem | Possible Cause | Solution |
|---|---|---|
| Fork feels too soft or dives excessively | Incorrect oil viscosity (too thin), not enough oil, or worn internal components. | Use the correct oil viscosity. Increase oil level slightly or check air gap. Inspect fork internals for wear. |
| Fork feels too harsh or stiff | Incorrect oil viscosity (too thick), too much oil (small air gap), or air trapped in the system. | Use the correct oil viscosity. Reduce oil level slightly or increase air gap. Ensure oil was added slowly to minimise air. |
| Oil leaks from fork seals | Damaged seals, worn fork stanchions, or improper installation. | Replace fork seals. Inspect stanchions for damage. Ensure correct seal installation. |
| Uneven handling or performance between fork legs | Inconsistent oil levels or air gaps between the two fork legs. | Re-check and ensure both fork legs have precisely the same amount of oil and air gap. |
Frequently Asked Questions (FAQs)
Q1: How often should I change my fork oil on a BMW F700GS?
It's generally recommended to change the fork oil every 15,000 to 20,000 miles, or annually, whichever comes first. However, if you ride in harsh conditions (e.g., dirt roads, heavy rain), you might consider doing it more frequently.
Q2: Can I use a different weight of fork oil?
While some riders experiment with different oil weights to tune suspension feel, it's best to stick to the manufacturer's recommendation for your F700GS unless you have a specific reason and understand the implications. Using an incorrect viscosity can negatively affect damping and potentially damage internal components.
Q3: What is the correct oil level or air gap for my F700GS forks?
Consult your owner's manual or a workshop manual for the precise specification. As mentioned, a typical range is often around 100-150mm, but your model may differ. Consistency between the two legs is paramount.
Q4: Do I need to replace the fork seals while changing the oil?
It's not strictly necessary if your seals are in good condition. However, if you're approaching the recommended service interval for seals, or if you notice any signs of leakage, it's a good idea to replace them at the same time, as much of the labour is the same.
Q5: My forks feel harsh in the mid-stroke. What can I do?
A common cause of mid-stroke harshness is having too much oil, resulting in a smaller air gap. Try reducing the oil level slightly (e.g., by 5-10ml per leg) or increasing the air gap to see if this improves the feel.
Conclusion
Performing a fork oil change on your BMW F700GS is a rewarding maintenance task that can dramatically improve your bike's handling and comfort. By following these steps, using the correct parts, and paying attention to detail, you can ensure your suspension performs at its best, making every ride more enjoyable and safer. Remember, proper maintenance is key to a long and happy life for your motorcycle.
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