Sort your bike's leaky fork seals

That tell-tale oil trace means it’s time to replace those worn-out seals

Sorting your seals

It’s one of the mysteries of modern motorcycling – how fork seals can leak even though they haven’t done any work! In this week’s How To, I replaced the fork seal on my race bike because it has obviously started to leak, amazingly having done only one meeting in the last year – less than 100 track miles. It’s not alone – I’ve also got a cherished Ducati 999S that’s done 200 miles in the past year, and now also has a leaking fork seal. So that will have to be the next job on the bench! For whatever reason, fork seals don’t like being inactive. So if you’ve got a bike you don’t ride very often, it’s well worth giving the forks a wipe over with a paper towel to check for oil weeps – the tell-tale sign of a blown seal.

One thing I will stress if you’re considering replacing a seal is always check your workshop manual. Although the steps in this How To are fundamentally the same for all forks, there are subtle differences for USD and right-way up forks. Also, while the forks are stripped and being cleaned, why stop at replacing just the seals? If your bike is of a certain age you might as well replace the internal bushes and O-rings, too. You can get model specific service kits that’ll have everything you need.

1 – Make a stand

Bike Stand

A blown fork seal needs to be remedied quickly, as oil can drip down the fork leg and contaminate the braking surfaces. It’s a relatively straightforward task, but make sure you are confident with the strip down and re-build procedure. First, you need to raise the bike on a suitable stand that will allow the front wheel and forks to be removed.

2 – Pop the cap

Pop the cap

Before removing the fork legs, measure the distance the forks stick out above the top yoke, using a vernier or steel ruler. Also, make a note of the position of handlebars if they are the adjustable type. When you have done this it is a good idea to loosen the fork cap by half turn, as it will be easier than doing it later when the fork leg is off the bike.


Loosen the top yoke pinch bolt prior to loosening the fork cap

3 – Secure the calipers


Now undo the brake calipers and secure them using bungees, then remove the front wheel and undo any ancillary items that are attached to the forks, such as the brake hose clamps etc. Make sure any components and their fixings are laid out neatly to one side in an order that makes it logical when it comes to reassembly.

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