Specs on the non-adjustable Marzocchi forks?

[ducati_steve]

Hey, I'm talking to the guys over at Racetech about upgraded guts for my 2005 M620's forks (it seems that it is not something they currently offer).  I was just wondering if anyone has taken these apart and knows the specifications of the forks and innards (rate, dimensions, etc).  I'm just not sure if anyone has really put a lot of time into these guys, just because the Showas are so much better and not hard to find.

[ducpainter]

Hey, I'm talking to the guys over at Racetech about upgraded guts for my 2005 M620's forks (it seems that it is not something they currently offer).  I was just wondering if anyone has taken these apart and knows the specifications of the forks and innards (rate, dimensions, etc).  I'm just not sure if anyone has really put a lot of time into these guys, just because the Showas are so much better and not hard to find.

Traxxion Dynamics offers innards for them.

[clubhousemotorsports]

It becomes a matter of cost vs benefit.
I am sure that a set of marzzocci forks with a race tech damper unit, or traxxion or ohlins superbike... etc. would be better. but at the end of the day you have a set of marzzocci forks. And a $1000 hole in your wallet.
Would they work well?   you bet!
would they be worth much in resale? doubtful.
Would they look any better?  only if you take them apart.

I would do the simple low cost mods to these forks .
springs
oil height and viscosity changes

Either swap to another fork superbike or something else or bling it out with the ohlins.
At lest with the ohlins ten years later someone would love to buy your forks for decent $$$
good luck

[the_Journeyman]

I have the non-adjustable Marzoochi forks.  All I did was toss some new springs & oil in them.  Nice imrovement for only about $80.

JM

[Dietrich]

+1 Springs and oil go a long way.  There are a few spring oprions out there, I'm surprised Race Tech doesn't yet know which springs to use for these forks.  I'm pretty sure hyperpro has springs.  How much do you wiegh?  If you're under 180 lbs you can help the forks a lot by just getting the preload set correctly and some new oil.  That's what I did, went to lighter 5 wt oil to speed up the forks, and they're 100 times better than stock.

[Serenitynow]

How exactly does different weight oil in forks affect the ride? Thinner oil does what, thicker oil does what? Thanks!!

[clubhousemotorsports]

playing with oil can be chasing your tail because the oil change changes both rebound and compression.
Lighter oil makes your compression softer but also reduces rebound
thicker oil adds rebound but also makes compression harder.

Some times it is all you can do so you make a compromise. It can still be worth doing.

[Sgt_H]

Also see this thread http://ducatimonsterworldwide.org/index.php?topic=1902.msg21797#msg21797

It looks like Racetech has springs for $110 so I think that cost benefit to springs and oil is pretty good.

[Dietrich]

playing with oil can be chasing your tail because the oil change changes both rebound and compression.

On the Sport Classic Marzocchi forks one leg dampens rebound and the other dampens compression, so you actually could tune each leg (stroke) to be optimized. 

[clubhousemotorsports]

Actually
on the sport classic forks (and small damper rod m620/800) forks there is only a bottoming cone in the bottom of one leg.
No damping to speak of.

The first one I came across I thought it was a bad damper unit and had ducati warranty it, It was not broken.
They are all like this if you are lucky enough to have the small damper fork.

I have dissected the damper unit on you can see that by design there is very little damping going to happen there.

[scott_araujo]

Some Monster owners have reported one leg for rebound and one for compression, others have reported both legs doing both.  I think it depends on what was available when your particular Monster went down the assembly line.  The one leg doing both while the other does nothing is new but I certainly can believe it.  If you're lucky enough to have the one and one combo you can tune rebound and compression separately, otherwise they are linked.

To damp the movement oil gets squeezed through small openings in the fork internals.  Lighter oil, less damping, faster movement.  Heavier oil, more damping, slower movement.  You generally want the fork to react as quickly as possible without bouncing like a pogo stick.

Standard tubular forks really do just force the oil through small holes.  Ducatis have the more sophisticated cartridge fork.  In a cartridge fork the hole the oil is flowing through is controlled by a shim stack.  This is a stack of several small metal shims that can bend to move out of the way at different pressures.  Why?

Well, in forcing oil through a hole it takes more than twice the effort to force the oil through twice as fast.  So a standard fork that reacts well to small bumps that move the fork slowly generally is harsh over larger bumps that make the fork move quickly because you're starting to move that oil much faster and it takes a disproportionate effort.  Go with lighter oil and the big bumps are fine but it tends to pogo on smaller bumps because now there is insufficient damping.

Enter the cartridge fork.  The top shim makes a very small opening which is good for small bumps that move the fork slowly.  Along comes a big bump.  The fork moves fast, lots of pressure inside the fork, and the top shim bends back out of the way.  Now the flow of oil is controlled by the next shim down and the hole it creates.  By varying the number of shims, the size of the hole they create, and the pressure they bend back at you can tune the fork to be good at small bumps, big bumps, and everything in between.

The non-adjustable Marzocchi forks have a simple three shim stack that is not tunable.  While people often say this sucks it's still better than a lot of standard non-cartridge forks out there and you can tune it quite a bit with different springs, preload, oil weight, and oil height.  None of this is terribly convenient since you have to disassemble the forks to on degree or another for every adjustment.

On most forks the shim stack just screws into the top of the cartridge.  On Marzocchis the shim stack is dimpled into the inner fork to hold it in place.  I read somewhere a long time ago that if you drill out the dimples you can then remove the whole assembly and replace it with a standard threaded one that is now tunable.  Anyone know any more about this?

Scott

[clubhousemotorsports]

Showas have the cartridges that are dimpled and the marzzocci forks have more of an agressive crimp. Dissasembling a marzzocci damper unit is a one way job. Now if someone made a replacement cartridge tube you could easily rebuild them as well as the showas.

Other factors to think about thinner oils tend to get burnt up faster than thicker oils ( they break down sooner). dampers that are restrictive tend to heat the oil more and coupled with the thinner oil you would need more frequent oil changes.  This is why race bikes often get their suspension freshened each season.
Penske even calls for the valve shims to be replaced yearly. Now on street bikes this is a bit much, but you can see how they want the suspension maintained to be at its best.

The showa comperession valve that most of us have  uses a shim with holes in it and only a couple of other shims. due to its construction it is quite restrictive.  A shim stack set up (like a gold valve ) can have more shims than the stock valve and be much softer.

All of the small damper rod forks are one side only (by small I mean like 6mm small) . I would not be surprised if someone had the same damper unit in their mountain  bike.

[scott_araujo]

Thanks DucVet, I didn't know it was the Showas that could be drilled and disassembled.

Scott

[clubhousemotorsports]

The only way to know is to take everything apart that you get your hands on.

[Ducatiloo]

I have the non-adjustable Marzoochi forks.  All I did was toss some new springs & oil in them.  Nice imrovement for only about $80.

JM

Where did you get your springs from?  I can't find good ones for under $115.