When it comes to changing fluids in your chopper, the engine oil and gear oil get all the glory. People spend hours debating what types are better, how often to change, etc, etc, but when was the last time you thought about changing your fork oil? Although not as critical as the others, fork oil is essential to a properly functioning front end and on a chopper, which is usually your only piece of suspension. Since my chopper project isn’t to the point that it even needs fork oil, I’m going to demonstrate changing the fork oil on my old ’64 Panhead. It’s got a huge front end, so it should be easy to follow along with what I am doing… To start out, locate your drain screws which should be on the backside of each fork lower near the bottom.
I recommend spraying the drain screws thoroughly with a good penetrating oil like PB Blaster or Kroil to help loosen up any road grime that has worked its way into the threads.
While the penetrating oil is soaking, go find something to drain the old fluid into. It’s only going to be around 6 or 7 oz per side, so even just the bottom 1/3 of a two-liter soda bottle will work. Personally, I like to use a paint mixing container. That way I can measure exactly how much fluid comes out of each side and determine if I’ve had any leaks since the last fluid change.
Now in a perfect world, you would remove the drain plugs from the fork lowers and the fork oil would just drain out. Unfortunately, in the real world that is not always the case as both of my drain plugs were stripped and wouldn’t turn even after plenty of penetrating oil. I managed to get them removed with a set of vice grips, but the plugs did not survive and I had to order replacements.
While the lowers are draining, remove the top nuts from your fork tubes and compress the front end a few times to help force all the fork oil out.
Once the fork oil has drained, reinstall the drain plugs in your lowers. I like to use a little Teflon paste on the threads just to make sure I have a good seal.
For fork oil, I always recommend using a new bottle of oil from a reputable company like Motul. Like I said in the beginning, your front suspension is probably the only suspension on your chopper, so you want it to work as well as possible. Plus, it will probably be 5 or 6 years before you remember to change it again, so using a good fork oil is going to go a long way to keeping your front suspension operating smoothly as you rack up the miles.
My panhead calls for 6.5 oz of fork oil per leg if you are just doing a fork oil change (it takes 7 oz if you are rebuilding the forks). I’ve found the best tool for adding the correct amount of fork oil without half of it running down the sides of the fork tubes is a syringe. You’ll have to fill it multiple times, but you can be sure you added exactly the correct amount to each fork tube.
After the right amount of fork oil has been added to each fork tube, all that is left is to reinstall the top nuts. Late model front ends use o-ring seals, but since mine does not, I also like to put a little Teflon paste on the top nut threads before installation.
And that’s about it. Now your front end should be ready for 1,000’s of trouble-free miles.
Panhead Jim / @panhead_jim / Riding Vintage