Marzocchi 41.7 Non-USD Fork Damper Mods

[geodoc]

I've got a special Tonti-framed unit that's been fitted with 1995 Sport 1100 41.7mm dia. non-USD forks and triple clamps. The performance of the forks has been disappointing. Experimenting with different springs, various weight fork oils and the range of damper setting adjustment does not seem to improve its somewhat jarring and generally horrible ride.

Plan 'B' is to look further into adapting Race Tech or similar damper cartridges to hopefully improve things.

Has anyone here already tried this out? Satisfactory? Expensive? Maybe CBR600 dampers adapted?

George

 

[Skeeve]

I've got a special Tonti-framed unit that's been fitted with 1995 Sport 1100 41.7mm dia. non-USD forks and triple clamps. The performance of the forks has been disappointing. Experimenting with different springs, various weight fork oils and the range of damper setting adjustment does not seem to improve its somewhat jarring and generally horrible ride.

Plan 'B' is to look further into adapting Race Tech or similar damper cartridges to hopefully improve things.

Has anyone here already tried this out? Satisfactory? Expensive? Maybe CBR600 dampers adapted?

No experience to answer your questions, but some observations:

Wouldn't "Non-USD" translate to "RSU" ["Right Side Up"?]

Traditional damper-rod forks are largely unsatisfactory: that's why cartridge-emulators from Race-Tech & al came into existence! The nature of damper rod forks is such that almost all the diy performance mods from back in the day focused upon eliminating the compression damping by drilling out the respective orifices and getting the rebound damping correct by soldering up the rebound holes and redrilling them to a size that would work with whatever wt. fork oil was cited in the respective article [typically, something ridiculously light, like 5 wt., to minimize the amount of drilling & soldering involved], coupled with spring rate adjustments & oil ht. adjustments to get the most benefit from the trapped air spring... :geek:

Basically, whatever adjustments you have should begin with backing off the compression damping to zero as a starting point, dialing in the spring rate to get the correct sag, increasing rebound damping to the point where the suspension doesn't bounce, and then only increasing compression damping [if available] to the point where you don't bottom the forks if you jump on the binders hard.

In other words, get the cartridge emulators & don't look back... :side:

 

[GuzziMoto]

Yeah, you may be able to get them to work better with help from RaceTech or another suspension company.
But the stock forks off my Daytona (much like yours) were in need of some attention and I found it was cheaper to replace them with a front end of a GSXR. And now I have better suspension, better brakes, and a lighter front wheel.
Just sayin.....

 

[rocker59]

Moto International installed WP fork springs and 10wt oil in my Sport 1100's 41.7mm Marzocchis last winter.

I was/am really happy with the results. It really improved the bike.

I asked, and was told, that Racetech didn't make anything that would work with those forks.

 

[geodoc]

Hmmm............. I'll have to check with Greg Field down there to see what he has to say. I tried straight-wound 1 kg/mm items and while that rate worked beautifully in my 850T, in this bike weighing only about 5 lb. less, it didn't answer at all.

Maybe WP's are the silver bullit.

GD

Moto International installed WP fork springs and 10wt oil in my Sport 1100's 41.7mm Marzocchis last winter.

I was/am really happy with the results. It really improved the bike.

I asked, and was told, that Racetech didn't make anything that would work with those forks.

 

[guzzigray]

Hi George. Just to re-cap our conversation at PR. Here's a link to Maxton. They do the CBR 600 cartridge conversion. Love mine. They don't deal with US customers due to liability issues but if you decide you'd like to use them I can ship to my parents in the UK. http://www.maxtonsuspension.co.uk/

I have Marzocchi Strada 38mm forks on my street bike and the 38mm forks Maxton did for my racer are WAY better.

Also try here: http://www.cosentinoengineering.com/ind ... age450.htm

Obviously they do Brit stuff but maybe they do specials.

Good luck.

 

[ed]

1kg/mm is pretty stiff for the street. I'd drop that by around 20% to start. Put a zip tie around your fork leg and see just ho much suspension you use on the street. You may be surprised. That may be your problem.


Yes, you can adapt Racetech emulators. It requires machining of a spacer to sit on top of the damper rod. start with LIGHT oil around SAE 5 and tune to suit. M1Rs can be made to work well.



Ed

 

[GuzziMoto]

My Daytona with GSXR forks is running 1.1 Kg/mm springs up front. I am about 200 lbs and they work well.
I do prefer stiffer springs and less compression dampening, but Guzzi's are heavy.
To check your spring rate you need to measure/set your sag with and without rider on board. The zip-tie trick is useful for setting up your suspension but not directly related to spring rate.

 

[Fritzcoinc]

What should the air gap dimension be for the stock forks?

 

[greenman]

It's 170mm with standard springs. And 140mm with the WP progressive springs.
WP recommend 15wt oil, but I've used 10wt.

 

[Fritzcoinc]

It's 170mm with standard springs. And 140mm with the WP progressive springs.
WP recommend 15wt oil, but I've used 10wt.

Thanks! I found the info in the service manual, finially. I had not been putting in enough oil. I was using the owners manual recomendation of 360CC. In a drain and refil that would be close but in a dry fork refill 360cc makes about a 225mm air gap. What a dumb ass. I set 170mm. At least the forks work great now. Big difference.

But, how do you identify the WP springs? I have a 96 model and it has the WP rear.

 

[maru]

As it has been said damper rod forks are always going to be a compromise. This is because of the fixed size of the compression holes. In order to have decent levels of compression damping at low speed fork travel you will end up with too much compression damping when the fork tries to move thru a large portion of its travel in a short time. Imagine a deep sharp bump or a series of sharp bumps. This is because the oil can only move thru those holes so fast before it tries to hydrolock. Despite this a good damper rod fork will work better than a bad cartridge fork in more situations than one my think. You said you tried different springs but you did not say what you tried for spring rates. Generally i prefer stiff spring rates for damper rod forks. Contrary to what you might think it generally does not make the ride more harsh and lighter springs sometimes do. That is because excessive compression damping will make the suspension very hash and on a big hit with quick wheel/fork travel the the high speed compression can ramp up so quickly that it makes the ride very hash. The heavy spring slows fork travel and this reduces high speed compression damping in a damper rod fork because compression damping goes up sharply in these forks during high speed movement. Remember you can only move oil so fast thru a small fixed orifice. Also you have to carefully adjust your air gap with oil volume adjustments. The air gap effectively becomes an air spring. This becomes a supplemental spring towards the end of your travel and it is verrrrrrrrrrrry progressive. If the gap becomes too small you will really make the last bit of your travel stiff. Too much air gap will allow the fork to dive too easily and contrary to what one might think, this can also make the fork seem harsh because agin it aLLOWS the fork to dive too quickly thru its stroke which really amps up the compression damping. Basically these damper rods forks are better than the techies think, if they are set up right. Steve

 

[geodoc]

Heh Steve,

After contemplating the responses to the original posting, I happened to hear of an outfit in Asheville NC that has done (amongst others) a lot of work with late 80's to mid-90's Ducati forks. With they're being variations of the Marzocchi M1R's, as are the ones on the non-USD Sport 1100 forks that I have, I decided to call them up: http://motocd.com/

Rick, the guy who's place it is was most helpful and felt as though the forks were certainly worth having a look at to see what might be done to improve the ride (possible CBR600 cartridges?). To that end, I've sent the off to see what he figures along with the YSS shocks that even after an internal adjustment by the importer, had a similar harsh ride that could not be adjusted out.

So ................. we'll see.

George

As it has been said damper rod forks are always going to be a compromise. This is because of the fixed size of the compression holes. In order to have decent levels of compression damping at low speed fork travel you will end up with too much compression damping when the fork tries to move thru a large portion of its travel in a short time. Imagine a deep sharp bump or a series of sharp bumps. This is because the oil can only move thru those holes so fast before it tries to hydrolock. Despite this a good damper rod fork will work better than a bad cartridge fork in more situations than one my think. You said you tried different springs but you did not say what you tried for spring rates. Generally i prefer stiff spring rates for damper rod forks. Contrary to what you might think it generally does not make the ride more harsh and lighter springs sometimes do. That is because excessive compression damping will make the suspension very hash and on a big hit with quick wheel/fork travel the the high speed compression can ramp up so quickly that it makes the ride very hash. The heavy spring slows fork travel and this reduces high speed compression damping in a damper rod fork because compression damping goes up sharply in these forks during high speed movement. Remember you can only move oil so fast thru a small fixed orifice. Also you have to carefully adjust your air gap with oil volume adjustments. The air gap effectively becomes an air spring. This becomes a supplemental spring towards the end of your travel and it is verrrrrrrrrrrry progressive. If the gap becomes too small you will really make the last bit of your travel stiff. Too much air gap will allow the fork to dive too easily and contrary to what one might think, this can also make the fork seem harsh because agin it aLLOWS the fork to dive too quickly thru its stroke which really amps up the compression damping. Basically these damper rods forks are better than the techies think, if they are set up right. Steve

 

[jbu]

I was curious to hear about the end result. Did you get the forks back from Cogent engineering? What did they end up doing and how are the forks performing for you now?

 

[ghezzi]

Used to have a 2001 Cali Stone, non-adjustable conventional forks.
Riding be side it (swapped with a mate) you could continually see flashes of daylight under the front wheel.
Meaning the front tyre was bouncing off the road continuasly at a very rapid rate. That was conducive to front end slip, slides and twitches when cornering in the wet.

I sent my front end to Pete at Promeca in Melbourne, not sure of the internal mods but I believe he added his own version of an emulator.

Comparing it again with my mates Cali Stone, there was a visible difference in the fork action, as well as avery tangible change in the ride and handling. It was now very sure footed in the wet mountains.

My old 2nd hand MkIII Le Mans, was very harsh in the rear and no amount of suspension softening was improving things. Turned out the PO (aircraft engineer??) had done the swingarm pivot pins up to about 500ft/lbs before tightening the lock nuts to an equivalent pressure. Doh! The ride was good when these were reset properly.