Replacing front fork oil (Marzocchi)

[Bjorn]

There is something about front forks that make me not want to work on them. I dont know what it is, maybe the abundance of delicate parts, seals and o-rings. Anyway, i wanted to replace the fork oil for a long time but took every chance to postpone it

 

I could not find a how-to for this job with pictures, so i shot some:

 

See the manual for details regarding the removal of front wheels etc.

 

1. jack up the bike. I used a mini jack under the front side of the engine. remove the front mudguard and wheel.

 

2. unscrew both the small brass screw and the 22mm nut (fork adjustments). And count the turns in order to restore your setting later on. Don't know if this step is absolutely necessary, but I thought it would relieve tension from the fork.

 

 

3. Measure how much the forks are protruding from the top triple clamp, and write it down somewhere. Next you want to unscrew the top of the fork(s) see the red arrow. On this bike (ballabio) you need to remove the handlebars in order to fit a socket. Don't know how this works for the clip-on versions. One turn is enough, you want to do this now because the forks are held securely.

 

 

4. Loosen both the top- and bottom triple clamp and remove the fork(s). Next you can completely unscrew the top of the fork. I choose not to clamp anything in the vice in order to prevent damage. I did have a extra set of hands helping....

 

5. This is the tricky part. You need to remove the top from the rest of the fork. You need to get a 22mm wrench for the top part (also described at point 2 above) and a 19mm wrench for the bottom nut. This bottom nut is hidden underneath the spring (see red arrow, note that the bottom wrench is not fitted on the described nut). You need to push down the spring in order to access the nut. Just screw off the top bit.

 

6. remove the spring, plastic bushing and dampening rod. Pump out the old oil.

 

I had no history of any fork oil change. I was expecting lots of crap....... but surprisingly the oil did not look half bad. 

 

7. refill the forks with the required amount of oil. and pump several times to get the air bubble out.

 

8. reassemble in reversed order and see the manual for details. Pay attention to the alignment of the forks. Don't forget your settings.

 

The only thing i haven't found is the torque setting for the hollow front wheel axle. I did find 90-100Nm for the solid version. Can anyone point me in the right direction?

[Bjorn]

Almost forgot!

 

While servicing the front forks we inspected the wheel bearings. We where quite shocked about what we found on both sides:

 

 

Bike is 50k km old. Bearings look OEM. Thankfully they did not fail completely during a ride!!!

[docc]

Thanks, Bjorn!  I'll move this over to the "How To  . . ." subforum as the comments settle down.

 

When doing this for the first time, I had to remove the internal cartridge from the bottom of the fork leg and discovered a set screw inserted from the inboard side of the lower fork housing. It does not appear in any of the diagrams we looked at in those days for the early Marzocchi of 1999-2002.

[luhbo]

Thanks for the nice and detailed write up.

 

Let me add that it's better to fill up only one side with the recommended volume, the other side then should be filled up to the same level as the first one. The resulting ammount of oil might be different, but this way the more important resulting air volume will be the same in both legs.

 

Hubert

[Bjorn]

Thats why i made a small how-to, because i could not find pics or diagrams of the late version marzocchi forks.

 

@luhbo, You are right. We used a measuring cup for the volume of oil. Pumping is required for bikes with a prescribed oil Level instead of volume.

[Bjorn]

We bought new bearings for the front wheel and fitted them. The old one were not keen on leaving the wheel haha.

 

 

Anyways i want to reassemble the whole thing and have serious doubts about the write-up in the Guzzi manual. I have posted a picture below of the ''updated version aka post '02'' manual. They quoted parts of the original manual. See the picture below >>

 

Now if you look at the last 4 points, the say:

• tighten the locking nut onto the wheel spindle. (not to the required torque??)
• tighten the 4 clamping screws.
• Then set the wheel spindle to the required torque.

To me this makes no sense. If you tighten the 4 clamping screws before setting the torque on the axle wouldn't you pinch the entire forks??

My commonsense tells me to fully tighten the axle nut to the required torque (90Nm), and then tighten the clamping screws. This way you can never pinch the forks.

 

 

Detail: the axle and wheel are only clamped together to the LHS fork. The RHS of the axle can (in theory) move freely throughout the fork. And is only held in place by the clamping screws.

[Bjorn]

Almost forgot:

 

Best wishes to everybody! May it be a year with lots of (non-mandatory) wrenching and a lot of save miles!

[GuzziMoto]

I would agree it seems a bit odd, but as I read it if you tighten the FOUR clamping screws before setting the axle nut torque it would not pinch the fork at all as the torque would be between the nut and the two pinch bolts (clamping screws) that are next to the axle nut. I don't have the version of forks you have, the wife's is an early red frame model. But my standard practice is to tighten the axle nut, which is normally floating on the other end so it does not pinch the forks, and then tighten the pinch bolts. I typically do not consult the manual for things I already know how to do.

[nobleswood]

Bjorn,

 

I'm hoping to get to service the forks on my bike soon so I was interested to see you dive into this oil change. I have a 2004 V11 Naked and started asking advice from the guys on the forum in

 

http://www.v11lemans.com/forums/index.php?showtopic=18735&hl=%2Bfork+%2Boil&do=findComment&comment=200058

 

And you joined in at some point I see.

 

My manual, which doesn't refer to the Ballabio at all, says 400cc of SAE10. Your manual gives different volumes for the Sport, 435cc and 452cc for yours. What is going to be the effect of the different volumes? And what airgap did you end up with ?

[Bjorn]

I just ''forgot'' what the manual stated and used my common sense (maybe I can slowly start calling it knowledge   ). anyways the whole bike is back together and im a happy camper.

 

@ nobleswood: there is a update manual for the later types. Im sure you can find in on the forum, but here is a different (excellent) source:

 

http://www.thisoldtractor.com/moto_guzzi_misc_workshop_manuals___shop_manuals___service_manuals.html

 

Just scroll down until you see the ''updated'' v11 version of the manual. this version has some updated info about the bikes but often falls back on the original manual.

 

It might be a bit confusing since we mentioned pumping the forks and all. But the manual for this bike does not state a airgap. It only states the required volume per fork. I cannot tell you the effect of different volumes in terms of handling etc. Im not really home in the whole suspension settings stuff anyways. Good luck wrenching!

[Zooter]

My guess is the volume of oil is less important than the volume of air, which is much easier to calibrate by the level of the oil.

 

When you guys say "pinch" the forks, is that causing the tubes to bind? I'm having a hard time visualising floating anything in the front axle.

[GuzziMoto]

Yes, I agree. It is really about the volume of air above the forks. The right amount adds a small bit of botttoming resistance. Too little air volume leads to limited travel and harsh ride, past that it can lead to blown seals. To much air volume above the oil leads to softer forks and more of a chance of bottoming, but as long as there is enough oil to satisfy the needs of the dampening components it will still work.

 

I am pretty sure he was referring to pinch the bottom of the forks together which results in the forks binding and not sliding up and down smoothly.

Normally when you tighten an axle nut on the front wheel the other side of the axle is floating in the other leg of the forks. It does not pull the one fork leg towards the other.

[Zooter]

Is there not a spacer on each side, between fork leg and inner bearing race? That's what I would expect to bear the torque of the axle nut. The fork legs wouldn't go anywhere until the bearing was inside out.

[nobleswood]

Bjorn, thanks for the link.

 

GuzziMoto, what is the 'right' amount ? There was a thread back in 2008 with Rachethead/hack saying 100 mm was the sweet spot for an airgap .

[GuzziMoto]

I don't know what the "right amount" is for your forks. Somewhere in the 100mm range is commonly used, but it depends on the amount of travel the forks have and how much of that air space above the fork oil level is taken up by things other then air. It is not the same number for all forks.

When I change the fork oil I usually measure the air gap before I start or measure the amount of oil I remove and add the same amount back in. That is assuming the forks work as I want them to already.

If I am changing things I usually start with a smaller air gap and I keep removing oil until the forks lose that harshness that comes from too much oil. I find it easier to come from that direction then trying to keep adding oil until it seems right as the changes from removing too much oil are more distinct.

You can certainly try 100mm, or you can go with, say, 90mm and keep removing a small (measured) amount each time until you like the way the forks feel.

My target is to have the air gap getting compressed to where it becomes a noticeable air spring just as the forks are nearing bottoming. That allows the springs and dampening to do their thing for most of the forks travel and the air spring effect only comes into play at the end to help soften any possible bottoming.

Everybody has their own preferences for how their forks/suspension work.