Fork Oil Change Procedure

[jwit6]

One fork was fully disassembled including removal of the cartridge damper assembly in order to replace a failed seal.

It was then reassembled and filled with 23oz of oil.

The other fork was not disassembled and was simply drained by removing the cap and inverting the fork to drain for a few hours.

Then it was refilled with 23oz of oil.

Did the cartridge/damper assy have to be removed in order for it to fully drain?

Or would it have drained adequately by being inverted?

Is this fork over filled?

 

[SLK50]

I think what's important is that the oil level is at the correct height and are equal in both legs.

Height is measured with caps and springs removed and forks compressed.

Top of oil to top of fork should be 92mm.

BTW, the small amount of oil remaining in the one fork should be inconsequential.

Complete dissassembly usually isn't required for an oil change.

 

[exskibum]

Did the cartridge/damper assy have to be removed in order for it to fully drain? Or would it have drained adequately by being inverted?

Is this fork over filled?

No to the first question, but you do need to pump the inner rod while inverted to get all the oil out, then hang it inverted for a bit. Best procedure is to do this and then put in some clean oil and do it again to flush all the dirty oil with metallic particles out. It doesn't take long to get pretty dirty and when you flush it, sometimes it takes a couple times (not full of oil, but enough to get the junk out) to get clear fluid draining. After that, as suggested above, it is the distance from the top of the fork (100mm, IIRC??) that is important. You measure with the spring out and tube compressed, inner rod pumped a few times upon filling and left to sit a half hour or for any air bubbles to rise -- then get the distance right. Motion Pro makes a great tool to get that distance right -- I might not do it myself without it.

So, I can't tell you if the other tube is overfilled, if oil levels in both forks are equal or if you're going to notice a difference. But if you do one again, you'd be best advised to fully drain, flush and refill the other as well -- and do them both correctly. If it were me and I had to replace one seal, I'd do it on both tubes.

 

[Geezer]

Exskibum has the right answer. Pump the piston on both legs to make sure you get all the air out and measure down from the top of the tube to the top of the oil. I used a thin metal ruler. Ideally you would want to measure before you drained the old oil so you know where you started from, but you don't always have that option.

 

[radman]

I never trust the oil level unless I've pumped the rod which fills the cartridge (pump several times till resistance is felt and you don't feel the "roughness" air imparts to the pumping action), then pump the entire tube a couple times, then I've let sit a couple minutes to wait for bubbles to surface.

 

[wheatonFJR]

I believe there might be a write-up on FJR Tech by Mike Carpenter...

 

[Ignacio]

I believe there might be a write-up on FJR Tech by Mike Carpenter...

Yep. It's here.

 

[exskibum]

Yep, that article is in my notebook, which is in the garage. If there's anyone who doesn't know about or use FJRtech, you're making it unnecessarily hard on yourself. Bin of Facts and all. There isn't any maintenance that I do on my FJR where I don't first see if Bounce or Warchild or Mike Carpenter or one of their contributing gurus wrote up the procedure. Their efforts for our benefit smoke the Yamaha service manual, though that's available for add'l info when I need it.

 

[exskibum]

I never trust the oil level unless I've pumped the rod which fills the cartridge (pump several times till resistance is felt and you don't feel the "roughness" air imparts to the pumping action), then pump the entire tube a couple times, then I've let sit a couple minutes to wait for bubbles to surface.

How the hell did Bust miss this one?!?

Look what he's got to work with: pump the rod, pump several times until you don't feel the roughness, pump the entire tube, and lubrication all over everything while you try to grip the big tube to pump it.

And the author is rad -- one of Bust's favorite targets. I'd think it's just that Bust is slipping, but with the Mizzus smackin' him upside the head recently, maybe there's more to it?

 

[jwit6]

I just removed the caps from both forks and measured the oil levels with the forks fully compressed. (Left the front wheel on but had to remove the bars to gain req'd clearance for the cartridges to rise). Both had 23 oz added the night before. The LH fork that was not disassembled (only hung inverted to drain without cartridge pumping) was 1.75 ounces higher than the RH fork which was fully disassembled. I was going to measure the oil height, but I didn't see where it was possible to remove the springs and be able to reinstall them without having to remove the forks entirely in order to invert them for reassembly. The reason being is that once you remove the 14mm nut on the damper rod and remove the cap, the damper rod will fall into the spacer rod beyond reach, and it appeared to me that gravity was going to be the only way to get it to poke back out for reassembly. (maybe you could compress the spring enough to do it, but that looked like a whole new challenge). Since I wasn't in the mood to yank the front end again I settled for matching the level in the LH fork to that in the RH fork which I knew had the correct amount..

So from my perspective, in order to fully empty a cartridge, you have to either pump then invert and pump and invert until it's empty, or fully remove the cartridge.

Next time I change the fork oil, I'm gonna raise it by the header pipes, leave the forks on the bike, remove only the front axle, loosen the handle bars, impact off the 6mm allens that secure the cartridge to the lower leg, then undo the caps and pull the cartriges right out the top. The aluminum spacer at the bottom of the cartridge may or may not come out with the cartridge. If they stay in I'll need to make sure I lift them once or twice to make sure all the oil drains. I don't believe there is enough room in the lower leg to allow the spacer to change it's basic orientation or get sideways. So I don't think it will make any difference on reassembly. The forks will fully drain right in the triple trees and you can clean up and drain the cartidges fully on the bench. Then reassemble with equal amounts of correctly measured oil in each leg.

Does this sound reasonable? It seems like a potentially quicker way to perform a fork oil change.

 

[Bustanut joker]

Why is everybody always pickin' on me?

Dunno bum, I guess I was awaitin' for somebody else



:jester:

 

[radman]

Invert and pump, and keep pumping until it's dry. I then add pretty much a full can of brake clean, pump that in, let soak a couple minutes, then drain using above again, gets a lot of crud out-and I do it yearly. Early on I added a second can of brake clean, but quit as the second can drained clean, so no need. There ya perve, plenty to work with should you feel the need....................

 

[Bustanut joker]

This is getting tempting.... Hold on I gotta "lube my tube"

When ya say brake clean, I take it it's not the aerosol stuff??

:jester:

 

[FJRBluesman]

One fork was fully disassembled including removal of the cartridge damper assembly in order to replace a failed seal.

One fork seal fails I'd also do the other fork, that's just me but, if one failed the other may not be far behind, and you have everything torn down that far.....

 

[radman]

This is getting tempting.... Hold on I gotta "lube my tube"
When ya say brake clean, I take it it's not the aerosol stuff??

:jester:

Yes, it is. My trusty fav, 3M 08880.