Fork oil level and quantity (GEN II)

[Unicycle52]

Fork oil

I've researched the forum and web and found lots of info on Gen 1 but can't seem to confirm Gen II information. My manual for Gen II says 23.5 oz, 92mm from top of fully compressed tube to oil with no spring installed. Upon draining I got about 21 oz out and had a measurement of about 110mm to the top of the tub. Upon refill with 23.5 oz (as per manual) I had a measurement in the 65mm range. One of these numbers can't be right.

I am not the original owner but I'm guessing this is the first time the oil has been changed at 13K miles.

I ended up sucking out about 2.25 oz to end up with a 100mm measurement. I am thinking about shooting for the difference between the original 110 measurement and the spec of 92.

Suited up I top out at about 145 and rarely carry a passenger.

Can anyone confirm the measurement and the quantity.

Bill

 

[Queensland Ken]

You are right, you will find a discrepancy in the service manual between the measured quantity and the air gap.

The air gap plays a part in compression dampening, if 100mm seems too soft, add some oil.

I set mine to 90mm, seems fine.

 

[escapefjrtist]

92mm is the correct oil level for stock GENII forks. IF you have aftermarket valving, then oil level varies depending on what you have.

--G

 

[Fred W]

My guess is that you did not actually get all of the old oil out of the forks, so when you added the correct amount of oil the level was too high. No biggee, sucking some out is/was the correct thing to do. The actual volume of oil is of no consequence to the damping. It is the amount of air you have in the headspace that matters. That air is trapped inside the fork tubes so when you compress them the air also compresses and acts as a progressive helper spring to the main wire spring in the fork leg.

You can adjust the air space (within reason) to increase or decrease the effective spring rate. You do not want the level to be so low that the dampers start sucking air bubbles and screw up the damping, nor so high that you have no air space left in the the fork at full compression as that would blow the seals out on a big bump (what a mess!) The OE spec height is a good starting point and move a little up or down from there.

 

[Unicycle52]

Fred,

I plunged and pumped repeatedly (many times) to drain the forks. I actually flush them out 2 or 3 times with ATF until they drain clean.

My biggest concern was not the quantity that came out originally, but the fact that the original air gap was 110mm instead of the 92mm that the book called for. Then when I filled to spec and had an air gap of around 65mm I knew that one of the spec's must be wrong. (Yes, I plunged both the damping rod and the inner tube a dozen times or more and let them set a bit.)

I set the air gap to 100mm figuring it gives me room for adjustment with the adjusters and I can ad more probably easier than taking some out.

Bill

 

[RaYzerman19]

If you did not remove the cartridges you likely didn't get the entire amount out. In that case, flushing with ATF might mean some residual ATF remained, same net result. Regardless, that shouldn't hurt anything. The correct amount of fill is determined by the air gap you choose. You're in the ballpark, go ride.

 

[NMRoadRunner]

Found the same thing a couple of weeks ago. Measured amount was less than needed to hit the air gap distance after complete rebuild. I filled to hit the air gap dimension. Haven't properly tested yet though, been out of town working. Going to check it out today. I've always used the air gap method of filling forks since back in the flat track days. Good weather and good riding!

As an added note, I found the right side bushings worn badly, left side not so much.. Does that mean anything?