Changing fork oil

[nampus]

I want to replace the oil in the rebound leg of my husky for a thicker grade oil because I have almost no rebound damping regardless of adjustment. 

I've never opened a forkleg up before, but this is what I am planning to do:

Remove front wheel and fender

Release top pinch bolt on rebound leg

Loosen the fork cap. 

Remove fork leg

Open top cap completely. 

Pour out old oil

Pump fork cap to empty the cartridge 

Pour out the remaining oil

Let drip for a while

Pour in new oil

Screw the fork cap back on

Pump it a couple times to bleed the air out of the cartridge. 

Reinstall fork leg but keep top pinch bolt undone 

Torque fork cap 

Torque pinchbolt. 

Is there anything I'm missing? 

What about the adjuster on the top, do I leave it as is, or do I need to put in fully closed or fully open before opening the forkleg?

@Sideshow Pob you seem pretty clued up on suspension, any tips or tricks are greatly appreciated! 

 

[Sideshow Pob]

Firstly, do you have the full range of adjustment (clicks) available as per the service manual? If a fork has been taken apart and the cartridge removed, it’s a frequent fault to rebuild it incorrectly and this results in reducing the amount of rebound adjustment available. Although you would nearly always still have ‘maximum’ when fully wound in, you would just not be able to get to the ‘minimum’ settings.

If you find that you don’t have the full range then it might be worth having the fork professionally serviced.

But what you’ve outlined is an acceptable method to change fork oil, sometimes referred to as ‘quick and dirty’. A full service would clean out any ‘sludge’ build up sitting in the bottom of the fork. 

Its quite amazing how much oil is retained inside the cartridge even after you feel it has been pumped and drained. But just do the best job you can and get as much of the old oil out as you can and of course, measure as accurately as possible what has been removed.  I would recommend leaving it to drain overnight. You won’t be able to set an air gap if you’re not going to be removing the spring so you are relying on the quantity of oil coming out as being correct. So carefully put in the same quantity of new oil as you’ve taken out.

I hope that’s a bit of help for you.

 

[nampus]

7 hours ago, Sideshow Pob said:

Firstly, do you have the full range of adjustment (clicks) available as per the service manual? If a fork has been taken apart and the cartridge removed, it’s a frequent fault to rebuild it incorrectly and this results in reducing the amount of rebound adjustment available. Although you would nearly always still have ‘maximum’ when fully wound in, you would just not be able to get to the ‘minimum’ settings.

If you find that you don’t have the full range then it might be worth having the fork professionally serviced.

But what you’ve outlined is an acceptable method to change fork oil, sometimes referred to as ‘quick and dirty’. A full service would clean out any ‘sludge’ build up sitting in the bottom of the fork. 

Its quite amazing how much oil is retained inside the cartridge even after you feel it has been pumped and drained. But just do the best job you can and get as much of the old oil out as you can and of course, measure as accurately as possible what has been removed.  I would recommend leaving it to drain overnight. You won’t be able to set an air gap if you’re not going to be removing the spring so you are relying on the quantity of oil coming out as being correct. So carefully put in the same quantity of new oil as you’ve taken out.

I hope that’s a bit of help for you.

 

Definitely helpful! Thanks a lot! 

I'm 99,9% sure I have the full adjustment available, I couldn't find the full adjustment in the manual, but I'll check the service manual again tonight when I get home from work. All I could find so far have been suggested settings for sport, standard and comfort with comfort being 19 clicks out and I've got 22 clicks of adjustment if I'm not mistaken, so I'm assuming that is the maximum range. 

I've bought the bike new, and the forks have never been opened, and there is a difference when bouncing the forks up and down between minimum and maximum, it's just hardly noticeable. 

And with the rebound completely closed, it still bounces up and down. 

Plan is to hopefully get the rebound to a somewhat acceptable level. And then hopefully in the not to distant future get the forks done properly and change the shock as well. 

 

[blow_away]

Once you have drained the old oil, fill with brake cleaner, pump the fork a few times, then leave upside down to drain fully. 

It's not as good as a complete strip down, but it will get rid of some of the sludge. 

Prepare yourself for the smell too 🤢

[Sideshow Pob]

49 minutes ago, blow_away said:

Once you have drained the old oil, fill with brake cleaner, pump the fork a few times, then leave upside down to drain fully. 

It's not as good as a complete strip down, but it will get rid of some of the sludge. 

Prepare yourself for the smell too 🤢

Yup, that would help to shift a lot of it.

[nampus]

Thanks guys, I've got plenty of brake cleaner so I'll do that too. 

There's only 3500km on the bike, so I'm hoping the smell is not going to be to bad 🤞🏻🤐

[chris_c]

Don't forget to prepare yourself for the possibility of spring pressure that may be present when you remove the cap.

(you really don't want to have to visit A and E at the moment matey)

Safety Glasses just in case.

[nampus]

Good point! 

[nampus]

We're in business 

A cheap bicycle stand makes for a pretty handy forkleg holder 👌🏻

And the Abba skylift is great for these kind of jobs too. 

 

[HOGG]

I don't know weather to do this on the zx6r or to send them off for a full refurb...

[nampus]

1 hour ago, HOGG said:

I don't know weather to do this on the zx6r or to send them off for a full refurb...

Depends what your plans are with the bike and if you have the tools and ability to do it yourself. 

If you can do it yourself changing just the fork oil will cost you less than 20 pounds. 

I got a liter of fork oil (which is enough for both legs on my bike) for €13,95. 

If you want to do it properly, and want to keep your bike for a considerable time, and considering the age of your bike, get them serviced properly. 

But that will be a tad more expensive. 

 

[nampus]

Since the oil was looking a lot better than expected and it didn't even smell, and the amount that came out was very close to the amount stated in the manual, I decided to skip the dripping overnight and cleaning the leg out with brake cleaner. 

Filled the leg with fresh oil, pumped it a couple times to purge the air from the cartridge and reinstalled the forkleg. 

Bike is back on it's wheels again.

The difference between adjustment fully open en fully closed seems a little more noticeable than before. But with the adjustment fully closed it's still not enough unfortunately. 

Not the difference I had hoped 😒

[blow_away]

Sounds like it's time for a revalve.

http://www.mhracing.com

[nampus]

Yes it probably needs to be looked at by an adult. 

I'll try someone in my own country first though 😉 but thanks for the suggestion. 

In the meantime I've gone and paid for the premium subscription to Dave moss' channel. 

And in his Vitpilen video he sets up two bikes. They both start out more bouncy than mine (one has the adjusters fully open 🤐) but he then sets them to about 6 clicks from fully closed, and the adjusters actually make a massive difference. Whereas mine hardly makes a difference between fully open of fully closed. So I'm starting to think something is faulty internally. 

[TLRS]

Did you talk to your dealer about this, maybe they can help?

[nampus]

No I haven't, but I'd rather just go to an independent suspension specialist. 

[blow_away]

What weight oil did you put in?

Now that you know you can do it easily and cheaply, maybe go for a different weight of oil.

[nampus]

The manual says 4w oil, I've put 7,5w in. 

But it's not just that there is not enough damping. The adjuster hardly makes a difference, which is what worries me the most. 

[David W]

31 minutes ago, nampus said:

The manual says 4w oil, I've put 7,5w in. 

But it's not just that there is not enough damping. The adjuster hardly makes a difference, which is what worries me the most. 

Don’t be surprised that the adjusters do nothing. Standard bike suspension is cheap with no differences between wide open and fully closed.

[nampus]

1 hour ago, David W said:

Don’t be surprised that the adjusters do nothing. Standard bike suspension is cheap with no differences between wide open and fully closed.

I wouldn't normally, but I've seen in the Dave Moss video about the vitpilen I watched, that the adjuster can make a significant difference. 

 

[svboy]

When you reassembled your forks, did you make sure the rebound needle was seated (lightly) into its female with the clicker in the fully closed position and with the clicker positioned on the damper rod so that you have the factory range of clicks available? Controlling rebound speed is very important. Assuming you have set sags and the springs are right for your weight then rebound is next on the list. If the clicker is not having enough effect then rebound can be fine tuned with fluid level/air gap. Less fluid, slower rebound, more fluid faster rebound. Use 10 cc increments to experiment. 

[nampus]

I never took the forks apart, all I did was open the top cap, dump the oil, pour in fresh oil (same quantity as what came out) and close the top cap again. 

The springs are to light for me. That's another reason why I need to see a professional anyway. 

I've got 59mm of sag on the front. And there is no external preload adjustment. 

[nampus]

Did a little over 300km's today. 

Expecting no improvent from the forks, I was pleasantly surprised to find it is a lot less bouncy! Especially noticeable on roundabouts when throwing the bike from left to right. 

Halfway in the ride I visited a suspension shop, they fiddled the adjusters a bit (added a bit of preload on the rear, and added about 6 clicks of damping all around) 

Bike is alot more stable now. 

To get it properly set up I need heavier springs in the front though. 

 

[svboy]

Or increase the length of your internal preload spacers. If you can get free sag of about 10-12 mm and then rider sag of 35 mm at the front doing this, then the springs are not too light for you. However if you have no free sag after compressing the springs using custom spacers, to obtain 35 mm rider sag, then indeed, it is time to try heavier front springs.

[nampus]

That might be an option as well. But that's for later. With the current settings, and the way it rides I'm happy to see out this season, and then get it sorted properly in the winter. 

 

[blow_away]

He shoots, he scores 😀

[Mark/Foggy]

Do not do that, if you need heavier springs, get heavier springs. Agreed that you can change the preload by messing with the spacer, but will never sort the problem out.

 

[Mark/Foggy]

Oh and 35mm is quite a lot for with rider sag,  

all depends on the bike of course, but 25 % of available travel, of front sag with rider, on board will put you in a good place to understand what springs should be in there. I am not thinking about having a pillion...let's face it nobody ever went well with a lunatic moving around on the back of a motorcycle.

Road only and having 35% would probably be ok, but would suggest that you are running progessive weight springs like OEM  or those Progressive after market springs.

Linear springs are the right way to go...you should be able to guess a number...if you can't I can probably guess for you..

[nampus]

Full travel is 135mm, so 25% would be almost 34mm. 35% would be 47mm.

Current sag is 59mm 🤐

Factory fitted springs are 6N/mm according to the manual. 

 

[David W]

6N springs? Are they out of a ballpoint pen?