How to Change Fork Oil on a Motorcycle
If you have to shrug when the term fork oil pops up, and turn back to the work on your bench, you are probably the guy who has a springer, girder or leaf spring fork in his chop, and generally keeps to Harleys before the 1949 vintage.
1949 is the year when Harley-Davidson introduced the red-hot Panhead "Hydra Glide" motorcycle, which came with a "hydra-ulic" front end. Steel tubes sliding on steel tubes, and deep down inside long springs swimming in oil raised the riding comfort to unheard of levels, reducing back-breaking potholes, back then a daily menace to riders, to minor bumps in the road.
With all this sliding action going on, it’s no wonder the oil eventually becomes worn and saturated with microscopic metal particles caused by abrasion, which makes regular oil changes necessary.
Changing fork oil on your Harley is therefore an important part of front-end maintenance. The viscosity of motorcycle fork oil can also be used to adjust the damping characteristics - and therefore the comfort - of hydraulic forks.
Originally, Harley-Davidson forks were filled with SAE 50 monograde motor oil, since dedicated fork oils did not yet exist at the time. Riders who want to replicate the same relatively firm damping today can use 30W fork oil, which provides a similar feel.
Over the years, Harley-Davidson used its own oil designations such as Type B, D, and E instead of the now-common 10W, 15W, or 20W viscosity ratings. As a rule of thumb:
- 30W fork oil - we recommend this for forks that were originally filled with SAE 50 motor oil (FL models up to 1977)
- 20W fork oil - we recommend this for most other forks or for riders who prefer firmer damping (similar to Harley-Davidson Heavy Performance oil)
- 15W fork oil - we recommend this as a replacement for the former Type E oil
- 10W fork oil - we recommend this as a replacement for the former Type B and D oils
Modern fork oils can also be mixed to achieve a custom viscosity, allowing riders to fine-tune the suspension feel. If you decide to create your own “viscocktail,” make sure you write down the mixing ratio so you can reproduce it at the next service.
Model specific quantities, the maintenance intervals and where to find the drain plugs are best looked up in the maintenance handbook that came with your bike, or in the relevant edition of Clymer’s handbooks. A quick read-through may help to order gaskets, if needed, and possibly replacement plugs, if the old ones look like they’ve had it. It’s not uncommon for drain plugs to be uncooperative, or strip, and generally can be a pain in the youknowwhere.
For a quick overview of model-specific amounts, have a look at our Fork Oil Filling Quantities (per side) tables to check the model-specific Harley fork oil capacity before you start.
Always consider calling our never sleeping service crew, who can take the strain out of the preparations at +499312506116 or send them an e-mail at service@wwag.com.
Let’s get started:
1) Set up your bike on a stand,
eg the Becker minilift, 97-441 and make sure that there’s no weight on your front wheel.
2) Fork oil tends to dribble down
the fork legs, and it’s a good idea to place an oil absorbent mat (81-000) under the front end to avoid a mess in your kitchen. If you want less cleaning up when finished, use the PanAm oil slide to direct the oil to the recipient of your choice.
3) Open the large fork tube plugs
on top of your fork with the correct size wrench, nut or the variable size Knipex plier wrench (very useful). This lets the oil drain much more freely. Open the two (left and right) drain plug screws and let drain the oil. A little patience helps to get out as much of the oil as possible.
4) If necessary clean or replace
the drain screws with new ones, using new gaskets if appropriate. Tighten to torque specs found in the handbook.
5) Now’s the moment for the new oil.
A funnel and a measuring beaker are your minimum equipment, but the PS oil level adjuster 91-891 is just the perfect tool to have round now. Find the correct quantity in your handbook, and fill each leg nice and slow to avoid spills and air bubbles.
6) Tighten those fork tube plugs again
(check your handbook for correct torque).
7) Time for a thorough check
that the oil only got where it was supposed to go, but not on your tires or brake discs.
All clean?
Bingo. You’re ready for the next pot hole filled summer.
From our experience we’d like to point out the possibility to
give us a call, should you encounter snags in the proceedings.
Our dudes have many thousands of two wheeled miles and countless hours spent wrenching under their belts and are ready to help.
Internet forums full of self declared experts may get you answers as well, but don’t bet the farm on them. When you’re wrenching on equipment your life may depend on, like forks, chassis components, brakes etcetera, get advice you can trust.