[primo661]

I'm sure most of you saw my post quoted below in my 4x bike setup thread about my Marzocchi DJ2. In short, the rebound damper locked up and when I opened my fork, I was disappointed with its build quality and lack of substance to it.

The rebound damper was made by SR Suntour and that was the problem, it did what every other 08 Marzocchi DJ fork does and the rebound damper jammed up and only gave 20mm of travel. Apart from that there wasn't the typical circlip at the base of the stantion holding the "top out" rod in place, instead they had crimped the end of the stantion in. It just generally gives me the impression that whoever designed it was thinking about saving money and not selling a quality product. My boxxer and the Psylo I had on my old jump bike were years ahead of my DJ in terms of build quality. Maybe I have just been spoilt, but If thats the case, I'm staying with Rock Shox so I stay spoilt.

I was tinkering on my DH bike last night and it got me thinking. I have an 04(HC2 damped) boxxer world cup and a spare set of internals lying around and I started wondering if it world be possible to fit my hc2 rebound damper into my DJ2 and after a bit of fiddling I figured out how to do it. All it would require is machining 1mm off the OD of the rebound base valve and a bit of creativity. And then I had a thought. Would it be possible to combine the HC2 compression and rebound assemblies to create a cartridge that does both?

My reasoning is this. The lower ports of the rebound damper only do two things. They allow suspension fluid to enter the damper shaft and then a small amount to leave the shaft during rebound(So far as I can tell). And the functional part of the compression assembly only occupies the lower 75mm or so of the compression "shaft". My question is, would it be possible to combine the compression damper and the top half of the rebound assembly to create a damper that handles both duties? I know it would limit my external adjustments to low speed compression only while rebound and high speed compression would be internal. I also realise the damping would not be that of a dirt jump fork but rather that of a DH race fork but ultimately, its going to be used more in a 4x/all mountain capacity than DJ(I just do alot more of the first two than the latter). Im fairly confident that playing with oil weights, I'll be able to achieve something better than the fork was originally. And even If I cant, this is more for the hell of it and an experiment than anything else especially since I'm thinking of doing my thesis(I'm studying mech eng) on hydraulic dampers. If you guys would like pictures to explain what I am saying better, let me know and I'll put them up.

Thanks in advance.
Andrew

 

[LOOnatic]

I like your creativity but you might wanna consult UDI, Socket etc for such a procedure.
And add some fluid resistance discs.....

 

[primo661]

Thanks, I was hoping they'd chip in, but I might just send them a PM just incase.

 

[time-bomb]

Not that I will be embarking on a similar experiment but I would be interested in reading what you come up with. If either PMs w/a response, get their permission to publish here. This thread has the potential to have some good mod info in it and may get referenced in Sandwich's sticky.

Good luck, sounds like a cool idea.

 

[primo661]

Having not got replies from either Socket or Udi, I decided to give it a shot anyways. I did exactly what I explained in my initial post. After machining the bush I need last night, I set about assembling the new damper and my fork today. It ended up working extremely well, suprisingly! The compression damping is almost dead on, first try, although the rebound is a little fast and it still tops out though so I need to adjust that after my exam tomorrow. One major criticism of Marzocchi is that they never designed the fork with a negative air spring which makes running even a remotely fast rebound without the fork topping out impossible but I can deal with the top out until I get my pike as long as the fork continues performing as it does now. Other than that, my HC2 damped DJ2 is a dream to ride. My brother is already trying to find a way to take it off my hands. I'll write up a proper review one I get a chance to really put it through its paces!

 

[DHPeteinSC]

I like your creativity but you might wanna consult UDI, Socket etc for such a procedure.
And add some Moar Shimz.....

Fixed

 

[cjcrashesalot]

The compression damping is almost dead on, first try, although the rebound is a little fast and it still tops out though so I need to adjust that after my exam tomorrow. One major criticism of Marzocchi is that they never designed the fork with a negative air spring which makes running even a remotely fast rebound without the fork topping out impossible but I can deal with the top out until I get my pike as long as the fork continues performing as it does now.

Can't you just find a suitable spring at the hardware store and stuff it in there as a topout spring?

 

[primo661]

There is what appears to be a topout spring in the spring side but really stiff and its still making a noise when it tops out. I can only assume its the sound of the bottom of the topout spring making contact with the bottom of the stantion. Would a longer, softer spring possibly do the trick?

 

[Steve M]

There is what appears to be a topout spring in the spring side but really stiff and its still making a noise when it tops out. I can only assume its the sound of the bottom of the topout spring making contact with the bottom of the stantion. Would a longer, softer spring possibly do the trick?

Sorry for not replying to your PM, glad you got your mod happening cos at first I had no real idea what you were actually trying to do. Sounds cool anyway, though one issue with the HC2 damping (as you may have noticed) is the ported rebound damper - which makes it harder to get much low-speed rebound without having excessive high speed rebound (ie the fork packing up - not really a problem on dirtjump forks).

Anyway - yeah longer/softer spring will help, you could also try putting some kind of soft material in there, like a thick o-ring between the top out spring and the damper seal head.

 

[primo661]

Dont stress Socket. Thanks, I'll give both of those solutions a try. The problem with HC2 as far as a DJ fork goes is you pretty much cant get enough low speed rebound at all, although I've got one or two ideas in mind to try fix it. We'll see how they work out. I have a feeling this is going to take a while slowly tweaking until I get the reound dialed.

 

[Udi]

Yeah I'm slack as, I think Socket covered everything - but for the topout spring, see if you can find something fatter than an o-ring. You can usually pull good conical topout bumpers out of trashed out old forks (RST's, old RS's etc).

Good luck with it, and nice one getting it going.

 

[Steve M]

Just thought of something - don't the rebound and compression check valves (in the bases of the stanchions) in the respective sides of the HC2 damper run in opposite directions? That might be why you're finding the rebound too fast - the oil is able to dump through the check valve during the rebound stroke. You could possibly just remove the check valve altogether and replace it with a solid bush/seal for positive oil displacement in both directions.

My memory is fuzzy though, I haven't worked on a HC2 fork for years.

 

[primo661]

Socket, you're right. I've done that already. I think its just a matter of opening the damper up, closing the rebound damper port and then taking it from there.

 

[primo661]

Oh, Udi, I think you might be onto something there. Even though the rebound is a little fast, its not too fast. And pretty much all the Marz DJ forks seem to make the same top out sound. At the base of the spring side(right) stantion there is a white plastic washer type thing that is below the top out spring and its not fixed so what I'm thinking could be happening is that when the fork tops out, the plastic washer is hitting on the base of the stantion and thats what is causing the noise. I'll try find a top out bumper to replace the plastic washer.

 

[primo661]

Okay, I know its been a while but I got the fork dialed now, the Rock Shox open bath damper I put together in true Frankenstein fashion is working perfectly as a sealed cartridge, with both high and low speed compression doing their jobs extremely well(considering that it was all put together by a first year engineering student). The fork works much better than it ever did stock but its still missing that edge that makes a good fork great, but since I cant actually fault its performance in a logical, constructive manner very much, I have come to convince myself that it has just lost that feeling deep down that I'm happy with the fork. I just dont even want to look at it anymore. Most likely due to the original problem that I had to do all this work to remedy. It is now waiting for its new, extremely happy and excited owner to pick up.

So I started playing with an old, reasonably new Marzocchi drop off 3 and I was suprised at how well it works out of the box compared to the DJ 2 which is both a newer and more "top end" fork. It doesn't top out, it has great build quality(cir-clips holding dampers in place instead of crimped stantions, real dampers and a proper air spring that comes with a functional negative air spring and more), its lighter and when lowered to 120mm, it performs flawlessly as a 4x/dj fork. This leaves me wondering why marzocchi changed a winning formula and subsequently botched a dirt jump fork when they had it right in front of them the whole time? The Drop off 3 is lighter, provides more adjustment, was cheaper and works alot better than a purpose built DJ/4x fork. So I take back all my unhappy mutterings about marzocchi's build quality and because their pre-move-to-taiwan forks seem to be the dogs bollocks