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Marzocchi Magnum(?) forks compression problem

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I have an 03 HuskyTE610 with Marzocchi Magnum forks, ie the old style, not upside down Shivers. They have a single compression adjuster on the left leg, and single rebound adjuster on the rhs.

I couldn't get any response when adjusting the compression adjuster, didn't make any noticable difference whether fully out or in.

Pulled it apart, and everything looks like it matches the parts fiche, and has standard adjustment shims etc.

Tested both sides with the springs out by pushing and pulling the shaft up and down. On the rebound side, there is a definite difference on the rebound speed depending on whether the adjuster rod is held in (closed) or left open, and it feels the same all the way through the stroke.

On the compression side though, there is very little resistance all the way down to about 2" from the end of the stroke, then the resistance kicks in, and it does differ depending on whether the adjuster is closed or open.

The recommended oil is 7.5. I've tried both 5 and 10 in it and apart from changing the general resistance overall, didn't change how the adjuster worked.

I assume this is not the way it should operate.

Does anyone have experience with these forks, and have any idea what might cause it.

Or should I just send it off to someone who knows what they are doing;-)

Cheers

Peter

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G'Day Pete, did you find out what was wrong? I have pulled apart my forks and I have the exact same problem on reassembly!

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Hi,

Did you have the problem before disassembly?

If you didn't that might tell us it is not a design flaw.

I have 'sort of' fixed mine, but it could all have been unnecessary if there was something wrong with the set up of the fork/shims etc..

The basic problem is that too much oil is escaping out the slot in the side of the cartridge, so the adjuster valve at the bottom never comes into play until the piston has passed the slot, which only happens in the last inch or two of travel.

It basically means that the adjuster is working, but only in that last inch, which is pretty useless.

As far as I can tell it is a basic design flaw. I can't see anything wrong with the internal set up of my fork, but I'm not an expert. I did talk to some of the suspension shops in Sydney and one at least seemed to remember having to close up the slot to get it to work.

I also found a diagram on the net from someone else who blocked the slot completely and redrilled 4 holes in the tube. This is apparently how the pre-97 versions of these forks worked, and he reckoned the slot was put in to cut the cost of construction.

So that's similar to what I did. I have silver soldered a plate over the middle of the slot. It leaves two little half cm slots at either end. This reduces the amount of oil that can get out the side and forces more of it through the adjuster at the bottom. It's not perfect but I am at least getting some compression damping now. I matched it roughly to the amount of rebound damping on the other side.

Cheers

Peter

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Unfortunately Pete, my magnums were working great before I took them apart and they do not have the mod. You can probably tell by now that I too am not a suspension expert!

I suspect the following items;

1. The nut/ cap clamping the floating piston, valve, shims etc is screwed on too tight or not tight enough. I noticed that the tighter I did the cap up, the valve pin and shims "locked" into place, unable to move/ rotate. There is no torque specified in the owners manual.I'll measure the float travel of the floating piston and perhaps we can compare.

2. The plug valve stuck or not operating correctly. It appears to work correctly, I can see a spring through the oil ports and it appears to be sliding a needle valve up and down. I do not have any infromation on how to tear the plug assembly down.

3. The upper nut/cap on the damper rod too tight on rod (the blue cap) or it's installed upside down. I will check on the other fork leg today.

Im in Melbourne ATM so if all else fails, I may get JayDee to have a look at them since he's used them before.

stay tuned - Can a resident expert give us any pointers here?

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I disassembled the compression leg today and noticed a few errors in my last assembly. Neverthless, the fork still does'nt feel correct. When the fork was on the bike, at full + compression clicks (clockwise), I could hardly push the forks down (static). The clicker has little or no effect now.

A few pics of todays work -

1. 08102009387.jpg

The correct way to install the check nut against the plug. Thread on the nut should be at the top of fork. According to the instruction manual, this plug should be tightened against the plug to 30Nm torque.

2. 08102009375.jpg

The floating piston assembly disassembled and assembly follows...

3. 08102009379.jpg

Cap goes first, with the 13mm "shim" facing towards the bottom of the fork - towards the shims.

4. 08102009381.jpg

Three shims installed - from the top of the fork, 15mm, 17mm, 19mm.

5. 08102009383.jpg

08102009384.jpg

Valve Pin next - pretty sure it is facing the right way. Recessed holes are exit holes at the top I believe.

6. 08102009385.jpg

Floating piston and nut installed yet to be tightened. The nut tightens onto the valve pin and stops is from rotating. I dont know if it is meant to do this, but i think it is, in order for the shims to work.

7. 08102009386.jpg

Floating piston assembly tightened. The "float" distance is measured as 2.9mm

All assembled with new Orings but blank... no effect when clickers clicked :busted: !

I wonder why? Is your setup similar Peter?

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I think mine does look different, but it is a couple of months since I looked at it.

I'll try to pull it out tomorrow and have a look. But sounds like we need someone with one working properly to compare to.

Cheers

Peter

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Pulled the fork out, looks very different to yours, so either we have different versions, or one has been upgraded.

This is what it looks like.

IMG_3784_800.jpg

All shims are locked tight, except for the spring loaded one on the far right.

Cheers

Peter

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Try KTMtalk in the bigbore/oldie but goodie section. I think your forks were wrong before. I don't think the compression knob should have any effect until the bottom of the stroke for the reasons mentioned by pete. I have those on my '96 KTM 300.

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