Gen 1 fork oil capacity/air gap problem

[robbo]

Helped Flooky to carry out a straightforward fork oil change today. However after filling the leg with the recommended 435cc of 5w and doing the necessary pumping to expel any air, the air gap was nowhere near the prescribed 140mm, more like 80mm, which to attain the correct air gap would have meant removing a high percentage of oil. I checked with a Yamaha dealership who agreed with my capacity/air gap dimensions. We decided to forego attaining the air gap and reassembled the forks. I've never encountered this problem before, as, having the proper air gap tool, you can normally slightly overfill the leg and suck out the excess oil to achieve the necessary gap. All suggestions greatly appreciated. Thanks in advance folks.

[PieEater]

Are the springs / cartridges OEM or replacement? If replacement and more bulky than the OEM ones then they would displace more oil and so you'd need less to achieve the same air gap.

A while back someone posted a mod where they fitted the internals and if I recall correctly the legs or stations of an early R6 to overcome a handling problem they were having. So it's not impossible for the forks not to be stock.

If it were me I would go for the correct air gap over the recommended amount of oil as my understanding is that too much oil can interfere with the effectiveness of the damping.

[robbo]

Hi PieEater,
The bikes only got about 7000 miles on it so this is more than likely the first time the forks have been apart.The air gap is achieved without the springs in the forks so the dimensions of the spring don't figure in the mystery.Thanks for your reply,all theories are welcome.

[Flooky]

I should add that the forks were drained well, upside down for at least three hours, so no left over oil.
Thanks for posting this Robbo.
And thanks for coming over.

[PieEater]

The air gap is achieved without the springs in the forks so the dimensions of the spring don't figure in the mystery.

That'll teach me to post  early on a Sunday morning before I've woken up    I've done two sets of forks this year so do know better 

[robbo]

PieEater,
No worries, all input is welcome,and spring diameter would have a bearing in fluid displacement if say the seals blew after a rebuild. It's a weird scenario as you'd expect the 435cc to be a tad over/under to achieve the correct air gap.It's as though there's a chamber in the slider that oil isn't getting to.Strange.

Flooky,
No worries matey, glad to help but odd how the maths did 't work out though. Hopefully we'll get a satisfactory solution.At the moment it's "leave the tools in the roll cab and keep my hands in my pockets". Very strange.

[teecee90]

More than likely they weren't fully drained. I left mine hanging overnight and still had to pump them several more times in the morning to get all the oil out. Even then they didn't quite take the full specified amount of oil. If I were you I'd take them off again and get the air gap right.

I assume you followed the correct procedure to bleed the air from the forks, particularly step 9

8. After filling the front fork leg, slowly stroke the damper rod up and down (at least ten times) to distribute the fork oil.Be sure to stroke the damper rod slowly because the fork oil may spurt out.
9. Slowly stroke the inner tube up and down to distribute the fork oil once more (1 stroke = about 150 mm). Be careful not to stroke the inner tube over 150 mm as this will cause air to enter. If the inner tube is stroke more than 150 mm, repeat steps (10) and (11).
10. Before checking the fork oil level, wait ten minutes until the oil has settled and the air bubbles have dispersed.

[robbo]

Yep teecee90,  followed all those instructions to the letter. Due to space constraints the bike had to be reassembled in order to be garaged. The only answer will be to take them off again when  we have access to a bigger garage and can spend more time. Never had this problem before and have worked on a few bikes in the past.

[Flooky]

Forgot to say, I measured what came out, 800cc.
so allowing for a bit on the rags etc that's about right.

[Flooky]

More than likely they weren't fully drained. I left mine hanging overnight and still had to pump them several more times in the morning to get all the oil out. Even then they didn't quite take the full specified amount of oil. If I were you I'd take them off again and get the air gap right.

I assume you followed the correct procedure to bleed the air from the forks, particularly step 9

8. After filling the front fork leg, slowly stroke the damper rod up and down (at least ten times) to distribute the fork oil.Be sure to stroke the damper rod slowly because the fork oil may spurt out.
9. Slowly stroke the inner tube up and down to distribute the fork oil once more (1 stroke = about 150 mm). Be careful not to stroke the inner tube over 150 mm as this will cause air to enter. If the inner tube is stroke more than 150 mm, repeat steps (10) and (11).
10. Before checking the fork oil level, wait ten minutes until the oil has settled and the air bubbles have dispersed.

cheers for the reply, so assuming yours were drained , the amount or the air gap is wrong ? I cant see dealers playing about draining and measuring fork oil, they would just drain and fill with the specified amount.

[old son]

What does it ride like?

[Flooky]

To be honest not bad, not been fast fast yet but its ok.but you know when something is on your mind?
Gonna ride Robbos when I get the chance to compare

[teecee90]

"cheers for the reply, so assuming yours were drained , the amount or the air gap is wrong ? I cant see dealers playing about draining and measuring fork oil, they would just drain and fill with the specified amount."



I made sure the air gap was spot on. I assume the slightly less oil was probably due to some residue still in the forks.


I wouldn't trust a dealer to do the job properly.