2003 Marzocchi Bomber MX comp air service

[hawkhill97]

Just got hold of a 2003 MX comp air set of bombers.

Rebound was totally undamped when I got them, so I took off the air caps and sure enough the oil level in each leg was very low indeed.

I found a manual here detailing how to adjust the rebound damping - it's a bit of a PITA, you need to reach down with a REALLY long allen key down the stanchion. I used a allen key bit gaffa taped to a chopstick, which seems to work!

http://my-sport.spb.ru/manual_1/2003%20bomber.pdf

The manual suggests (page 47) that all the damping takes place in the right hand fork length - is this correct? I ask as there is an identical looking valve present in the left leg. However, while the valve in the right leg stays at the bottom of the stanchion when compressing the fork, the (dummy?) valve in the left leg moves up and down on compressing the fork. Maybe I'm being thick but this seems a bit puzzling!

Assuming the manual is correct and the damping only takes place in the right leg, does this mean it's not necessary to add oil to the left leg as it's just dead weight and won't be doing anything?

Was going to stick in some 7.5wt or 10wt oil (filling up to 30mm below the top of the stanchion) - but like I say I'm unsure whether to do just the right leg, or both legs?

Other than popping up the wiper seals and giving them a clean/grease is there anything else I should do - is it worth removing the lowers to have a look at anything else while I'm at it (assume this is a simple matter of undoing the nuts at the bottom of each fork leg and pulling them off)?

Thanks for the help!

 

[hawkhill97]

The manual is a bit hopeless as covers all the different models of fork at the same time without any exploded diagrams, but another thing that was puzzling me... I can't see any springs anywhere, so assume this fork is entirely air sprung. But both right and left legs are positive springs - is there a negative (coil or air) spring hiding anywhere, or is that somehow not required (would have thought that would make them very reluctant to get moving initially with poor small bump compliance)?

Having had a look online lots of forums reference coil springs with air assisted pre-load, which is a concept I just don't get (I though spring pre-load was handled by screwing down a stop on top of the spring!). Like I say I can't see any springs in this fork and it compresses without resistance with the air pressure released from both sides, so I guess this must be referring to some other model of fork?

I've always wanted a set of bombers so really hoping I can get these working nicely for a new build I'm working on

 

[drcarlos]

You have it right in the first post. The damper is only in one leg, the other leg is the air spring, which is pretty much how 100% of good forks still work. The oil in the left side is lube for the air spring only and they only need about 5ml.
Your forks self equalises the pressure between positive and negative air chambers so only have one air valve. Some have 2 but not your model.
Usually the rebound speed adjuster is on the bottom of the leg on the damper side and not inside the damper leg itself, the manual would also indicate this, you may just be missing the external knob as they can fall off. You can usually adjust them by inserting a 2-3mm allen key into the hole in the bolt at the bottom of the damper leg.

 

[hawkhill97]

That's brilliant, thanks for confirming. I'll service it at the weekend.

Makes sense having +/- air springs that self equalise, didn't think of that.

Out of interest, if the left leg is the air springs and the right leg the damper, why is the right side also pressurised? As far as I understand it the damping happens solely from oil being forced through a small hole (ok posher forks will have blow-off valves etc too).

Is this a case of a second air spring being present as well as the damper in the right leg?

I'm usually quite mechanically minded, but suspension forks do boggle my brain a bit!

 

[hawkhill97]

Re:

Took the fork apart this afternoon - was easier than expected.

Both sides appeared identical, with damper rods and SSV assemblies in each leg, so I'm going to top them both up with ca 130ml of oil.

Unfortunately the rebound top-out springs on both sides had sheared - not sure how that could have happened?!

One option to get around this is to run heavier weight oil (maybe a mix of 10wt & 15wt) for more rebound damping. Another possible solution could be to get some tubular pipe insulation foam and put some around the lower part of the damper rod to act as an elastomer style spring.

I appreciate this is a bit of a bodge, but anyone have any thoughts on whether it's a sensible one?

 

[hawkhill97]

Re:

Think I'm going to give it a go.

The lack of a proper spring means there will be quite a bit of striction initially (almost like a platform feel..?), and it may lower the fork in its travel s touch.

Both of these things are ok with me for the build it's going on, which will be gravel oriented.

Just need to check the foam I've got in mind doesn't dissolve/ massively swell in fork oil or anything like that!

 

[hawkhill97]

Re:

All done now.

The foam pipe insulation makes an excellent top out bumper.

Rebound damping is a touch too much with the heavier oil - unfortunately there is no external adjustment knob on this fork, you need a fiddly long Allen bit to reach the damper inside the fork leg. I'll back it off a smidge and then should all be good!

Thinking of using a bit more foam as spacers to lower the fork, as the front end is still quite high.