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Easy Fork Oil Change On Baggers

Up on a lift with the fork expanded.

This morning I repeated the process again, on at a time, on both forks.
This time, I additionally compensated for the "hold up" in the system, just so I could measure things as precisely as possible. I added an extra 11 mls to the make it an even 330mls.

When I repeated the process on the left fork (the one that had pressure on it the first time I opened the drain screw), about 15-20 mls were left over. This was a little more than I expected, since I accounted for the hold up. But I am still learning about this.

When I moved to the right side fork, again I start with 330mls. This fork takes all 330mls and I shut the valve. When I take off the assembly, to put the plug back in, I don't even lose a drop because there is still a slight vacuum in the system.

In my previous post, I think I know why the new oil came flying out when I tried to put the plug in: My wife was giving me a hand and I didn't know it until I repeated the process this morning that she was squeezing the bottle ( I am using a restaurant style ketchup bottle for the oil). This slightly pressurized the system, but it also drove the entire volume of oil into the fork.

So to me, there is a difference between the forks. of at least 10mls and maybe as much as 20mls since the left side still had some vacuum on it when I broke the seal. I pulled the same vaccum (26") in both. I still can't explain why the left fork had pressure on it when I first opened the system but it appears that there is less volume in the left fork for some reason. Also, it seems that if I try to physically force the extra 10-20mls into the left fork, it does pressureize the system enough to have it come rushing back out.

Maybe I am making too much of this, simply because I am measureing too accurately for the system.

I feel like an idiot.

Maybe there is something hung up inside the fork (since this is the first fork oil change) that is changing the volume. Mabe after a little riding it will correct itself with the fresh oil helping things slide a bit better.

This is a really great technique for changing the fork oil and I still would recommend it to anyone, but it appears that I may have an issue with one of my forks (or maybe not).
 
About the only thing that comes to mind is a seal that isn't holding the vacuum otherwise they should both hold the same amount of oil.
 
Thanks for your thoughts. Next time I change the oil I will leave the gauge on for a while and check to see if there is a drop. It really is so easy to do, you could change the oil this way every week if you wanted to.

I wish I would have read about the fork oil change information earlier. As you (Mr. Data) commented on another post: When you see what the oil looks like you will want to change it out. That is definitely true!:11:

It seems to me that there was a lot of "sediment" in this oil at 24,000 miles of use. I have nothing to compare it to as this is my first motorcycle and first HD.:33:

I bothers me that the manual suggests service at 50,000 miles. I guess that means a complete rebuild no matter what, since the way the manual instructs changing the oil is to pretty much disassemble the fork. If you have it that far apart, you might as well replace the worn parts.
 
You will find that even with a minimal amount of miles on fresh oil that it will come out looking pretty nasty with the metallic like particles in it.

Also the front forks being a foreign make use a different oil in the factory fill. I believe it's a fish oil and the reason for the nasty smell when you drain it. This is also the reason for the big improvement over the factory fill when you do a service on them.

I like to find easier ways to do a service like the forks and this worked out very well. Nothing has to come apart.
 
So, it was bothering me. When I did the fork oil change a little while back, I could not get "the required amount" of oil in the left fork.

After a recent trip to North Carolina with a full load (my father and gear) on the UC, I put the bike up on the lift yesterday and drained the left fork.

Glider, I confirm that there was much sediment in the new oil. It was impressive after such a short period of time. At least there wasn't the "dead fish" smell.

The left fork took all of the oil this time. Additinonally, as a check, the fork held vaccuum at 26" for 3 minutes before I stopped the test and added the new oil. The only thing I can conclude is that something was bound in the shock on the left side, leaving the spring slightly compressed. This is why oil shot out like a fire hose when I took the left side drain plug out the very first time. It also explains why I could not get the same amount of oil back into the shock. I think after changing the oil and a heavy weight ride, the spring mechanism is back to an extended, uncompressed position.

Since this process is really easy and the fork oil is cheap, I changed the right side as well and now I feel better that I have the same amount in both forks. I don't know if this was just a "one time" event due to having lost some lubricative properties in the old (original) oil, sediment build up or both. Perhaps there is something wearing in the fork prematurely but it appears to be handling well and I haven't noticed any issues.

I figured I would post this in case someone else sees the same issue I did on the first shock oil change.
 
What I found that helps in those stubborn cases with the thicker oil is to draw the vacuum on the leg while the front wheel is still on the ground (assuming you have the bike on a lift) and after pulling the vacuum to the max on the leg you are working on, jack the bike wheel just off the ground just prior to adding the oil. This increases the vacuum in the leg to help pull the heavier oil into the leg.
Stock weights usually don't have a problem, it's just the heavier weights that do.

(added to the top post)
 
Hi Mr. Data, can this method be used on an 04 Road King. When I read the manual, it is a bit ambiguous over the front suspension ie whether it is a cartridge or air suspension. My reading makes me think it's a cartridge (therefore this method is no use).

Is there an easy method to change the oil in the cartridge type?

Either way, I am trying to firm up the front end a bit.

Thanks
 
good tip Mr. Data, i do it that way every time, makes changing the fluid a breeze.....there are a few models out there without the air suspension that even with the fork caps off and a funnel it is still tough to pour fork oil into the top of the fork (assuming you have left the forks on the bike) hear is something i learned that works awesome, go to the dealer and buy another fork cap and a bleader valve (same one that is on your brake calipers) drill a hole through the center of the fork cap and tap it to the same thread pitch as the bleeder valve.....now its the same concept as the air suspension tip the Mr. Data shared. hook your pump to the bleeder (the neumatic brake bleeder work great just turn it on and let it work) and watch it suck up the fluid. Hope that helps someone, i really like to do it that way, takes about 15 minutes to do fork oil. good luck!
 
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