Fork Oil Change
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 gets tired and saturated with microscopic metal particles due to abrasion, which makes regular change a necessity. The viscosity of fork oil can be used to adjust the damping characterisics (and levels of comfort) of hydraulic forks. SAE 30 W was standard on HDs up to 1978 (and up to ’84 on FL models). 30 weight is rather stiffish by today’s standards. It was replaced by 20 W later. If you appreciate a soft ride, go down to 15 W, or concoct your own "viscocktail" by mixing different viscosities. Make sure that you remember the mix ratio for next time.
Model specific quantities, the maintenance intervals and where to find the drain plugs are best looked up in the Let’s get started: