Regular cleaning of your dirt bike’s fork seals is vital to prevent dirt and debris from causing fork oil leaks. Oil seeping through the dust seal is a clear indication that it’s time to clean your fork seals.
To clean fork seals, start by placing the bike on a center stand and removing the fork guards. Pull down the dust seals to access the fork oil seals. Next, using a fork cleaner tool, clean the fork oil seal, removing any dirt or debris. Push the dust seals back on and reinstall the fork guards to complete the cleaning.
Leaking fork seals are a common issue, but it’s easy to fix them. In this guide, we will take a closer look at how to clean fork seals on a dirt bike. We also cover typical reasons for leaking dirt bike forks and how to fix leaky fork seals. We will also explore the cost of fork seal replacement in case you need to replace them.
In this article, you will learn:
- Common causes for leaking dirt bike forks
- Fork seal replacement cost on a dirt bike
Let’s get started.
Common Causes for Leaking Dirt Bike Forks
First of all, the fork legs, or sometimes referred as fork tubes, have two seals.
The lower one that you can see is the dust seal. The dust seal keeps dust, water, and other debris away from the oil seal and internal suspension parts.
The upper seal is the actual oil seal that prevents oil from leaking through the dust seal. Once the dirt reaches this oil seal, it begins slowly leaking.
Some oil will spill from the lower fork leg to the sidewalls of the upper fork leg. This oil is resting against the oil seal and pushed back to the reservoir when the fork leg is extended.
We recommend that you clean fork seals once a month or every time you ride in dusty or muddy conditions.
Typical scenarios that cause leaking fork seals are:
- Dirt, dust, water, or other debris inside the oil seal
- Too much oil in the fork
- Tear or incorrect installation of the oil seal
- Bent or damaged fork leg
Dirt in the Fork Oil Seal
This is by far the most common reason to leaking front forks. The front fork oil seals often start leaking when riding in either dusty, muddy, or wet conditions.
These conditions are harsh for the dust seals and they start collecting dirt. The dirt then works its way into the oil seal and, as a result, it starts leaking. This is by far the most common cause for leaky forks. Luckily, in this case you will only need to clean fork seals using a tool. No rebuilding of the dirt bike forks is needed.
Adding Too Much Fork Oil
Adding too much oil into the fork tube will cause issues. The suspension will feel harsh and when bottoming out, oil will leak out through the oil seals. The excessive oil increases pressure inside the fork tube and can cause leaky fork seals.
When adding fork oil, always measure the oil level and adjust to specifications. The service manual will explain the recommended oil amount. However, you can measure the oil level from the top of the fork tube.
Incorrect Fork Seal Installation
Sometimes the front fork seal leaks are caused by an incorrect installation of the oil seals. Another common cause for leaks is damaged oil seals during installation. A small tear usually happens when installing oil seals without a seal bullet. Also, not using lubrication when sliding the seals in place can also cause small tears in the fork oil seal.
Additionally, any spilled oil between the upper and lower fork leg can cause short term oil leaks after suspension maintenance. In small quantities it’s not dangerous but needs to be cleaned off.
Direct Impact to Lower Fork Leg
Hitting a rock hard enough to scrape the fork leg can cause a leak. In this case, you should notice the damage on the fork leg and clean fork seals. Otherwise, replacing them will not help with the leak.
Fork Seal Replacement Cost on a Dirt Bike
Dirt bike fork seals are not expensive. Replacing them though, will take some time. That is why we recommend cleaning them regularly to avoid having to take the fork legs apart.
The typical fork seal replacement cost is around $25 to $55. Typically, they last around 100 hours or so with regular cleaning. If you send the forks for oil service, they usually inspect and replace the seals when necessary.
Below, you will find replacement fork seals for KTM, Yamaha and Beta. Find exact version for your dirt bike here.
How to Clean Fork Seals
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Cleaning fork seals in most motorcycles and dirt bikes is simple. First, we need to access the fork legs. Next, slide out the dust seals and use a fork seal cleaning tool to remove any dirt inside the seals.
In our opinion, the most easiest tool for cleaning the front fork seals is the Fork Seal Doctor by Risk Racing. It cleans the dirt from the fork seals in just few minutes. It is easy to use both in the garage and trail side. You can find these type of tools to common 48mm fork size and for smaller 42mm forks.
Another great front fork seal cleaning tool is Seal Mate. While it may be slightly more difficult to use than the fork seal doctor, it gets the job done.
Other tools you can use include cotton swabs, thin plastic strips, and a cutoff plastic piece from a water bottle. If you use any of these methods, be careful not to tear or scratch the seal with sharp edges.
Step 1: Remove the Fork Guards to Access Leaking Fork Seals
Cleaning fork seals begins by removing the fork guards and then properly cleaning the fork dust seals and fork legs. If you are trail side, using a water bottle and paper towel usually works well.
Removing the fork guards is not necessary but it gives you a better access for cleaning the dust seal area. It also makes is easier to use the seal doctor.
Read also: How to adjust the front fork height and why
Step 2: Slide the Dust Seal Down the Fork Leg to Clean Fork Seals
Next, slide the dust seal down. Use a small flat head screwdriver or something similar to pry the seal down. Be careful not to damage the seal.
Push the edge between the seal and the fork leg metal edge. Wiggle the screwdriver to push the dust seal down about 1/16″. Next, continue around the dust seal prying it down in half an inch intervals until the dust seal is loose.
Step 3: Clean the Dust Seal With Water
Once you have slid the dust seal down, clean it properly with water or soapy water. Wipe off any sand, mud, and dust from the inside of the upper fork leg. Avoid pushing the dirt into the oil seal. Do not use a power washer or spray water upwards into the seals.
Step 4: Use the Fork Seal Doctor
Insert the fork seal doctor on the fork leg. Make sure the oil seal stamp is pointing up on the tool.
Push the fork doctor up so that the thin upper edge will slide under the fork oil seal. Next, start rotating the tool to break free any dirt inside the oil seal. Keep working with the tool until all dirt is cleaned. After each rotation, clean any dirt and debris from the fork as well as the tool. Repeat until no dirt is visible on the tool or around the seal.
Step 5: Reinstall the Dust Seal to Finish Cleaning Fork Seals
Clean the fork leg and the tool one more time and reinstall the dust seal. Be careful when installing the dust seal in place. Slide it all the way up straight and make sure it seats well. Using a small amount of suspension oil will help lubricate and protect the seal during the installation.
Read also: How to align dirt bike forks – aka twisted forks
Fork oil seals typically last around 100 hours of riding and before needing to be replaced. Cleaning fork seals regularly extends both the fork oil life and the fork oil and dust seal life.
We recommend packing the fork seal doctor into your trailside tool pack. Most front fork oil leaks will happen when riding in muddy or dusty conditions. This way, you can clean fork seals quickly trailside and continue riding.
Clean forks, fast trails!
- How to set up dirt bike suspension for trail riding
- Setting up dirt bike handlebars for trail riding
- How to rebuild dirt bike forks: a complete guide
- How to align dirt bike forks – aka twisted forks
- Single track riding tips for beginners
Last updated: February 24, 2023