Cleaning fork seals regularly on a dirt bike prevents dirt and debris from creating a leak between the fork seal and the fork leg. If you see oil seeping through the dust seal, it’s time to clean fork seals.
Cleaning fork seals on a dirt bike is simple. Start with placing the dirt bike on a center stand and removing the fork guards. Next, pull down the dust seals to access the fork oil seals. Using a fork cleaner tool, clean the fork oil seal. Finally, push the dust seals back on and reinstall the fork guards to complete the fork seal cleaning.
Let’s take a closer look at how to clean fork seals. More specifically, we cover typical reasons for leaking fork seals and how to fix leaking fork seals. We will also explore fork seal replacement cost in case you need to replace them.
Let’s get started.
Common Causes for Leaking Fork Seals
First of all, the fork legs have two seals.
The lower one that you can see is the dust seal. The dust seal is keeps the dust, water, and other debris away from the oil seal and the 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.
When the fork legs move up and down, some oil will spill from the lower fork leg to the sidewalls of the upper fork leg on the inverted fork. This oil is then resting against the oil seal and pushed back to the reservoir when the fork leg is extended to full length.
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 Will Cause Fork Oil Leaks
Have you noticed that the front fork oil seals often start leaking when riding in either very dry and dusty or muddy and 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, and no rebuilding of the dirt bike forks is needed.
Adding Too Much Fork Oil Will Cause Leaks
Adding too much oil into the fork leg 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 leg and can cause blown fork seals.
When adding fork oil, always measure the oil level and adjust to specifications. The service manual will explain the recommended oil amount but also the oil level measured from the top of the fork leg.
Incorrect Fork Seal Installation Causes Fork Oil Leaks
Sometimes the front fork seal leaks are caused by an incorrect installation of the oil seals or the fact that the oil seals got damaged when they were installed. A small tear usually happens if you are not using a seal bullet or tape over the sharp edges when installing the oil seal to the fork legs. Furthermore, not using proper 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 Can Cause Fork Oil Leaks
Another thing we have experienced to cause a leaking fork seal is hitting a rock so hard that it scraped the fork leg enough to 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.
Fork oil seals and dust seals typically cost around $50 to $85. Typically, they last around 100 hours or so with regular cleaning and should only be replaced if cleaning is not working. If you need to send the forks for service, they usually inspect and replace the seals when necessary as part of the regular maintenance and oil change.
How to Clean Fork Seals
This section contains affiliate links. If you use these links to buy something we may earn a commission at no additional cost to you. As an Amazon Affiliate we earn from qualifying purchases.
Cleaning fork seals in most motorcycles and dirt bikes is simple. We need to access the fork legs, 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. It cleans the dirt from the fork seals in just few minutes so that you don’t need to worry about leaks anymore. 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.
Other front fork seal cleaning tools you can use include cotton swabs, thin plastic strips of the size of a credit card, and a cutoff plastic piece from the side of 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 and 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 and then repeat until no dirt is visible.
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.
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 since most oil leaks will happen when riding in muddy or dusty conditions. This way, you can clean fork seals quickly trailside and continue riding.
So, keep your front fork seals clean and ride on!
Last updated: September 2nd, 2022