Fork Service recommendations?

[4corsa]

Dropping my 2003 Le Mans w/ 20k miles and Marzocchi forks at The Spare Part Co. in Philly (Guzzi specialists) this Saturday to have them change out the fork oil (has not been done in at least 9 years, as neither I nor the previous owner have had it done). There are no leaks, so the seals seem fine, and they recommend leaving them alone.  I'm happy with the way they work for me, so not looking to change cartridges. I saw another post where fork oil weight was discussed (5, 7, 10). I was planning to have them replace it with same. This is not something I know a lot about,  so if anyone has recommendations for anything to discuss with the mechanic, etc., kindly let me know.  Thanks in advance!

[docc]

I learned (from this forum), early on, that lighter oil performs better in our forks, so I chose 5 "wt."

Then, I learned (from this forum) that 5 "weight" can vary widely between manufacturers and even between one manufacturer's different products. After taking in Peter Verdone's discourse, and published tables, I chose BelRay 5W High Performance fork oil based upon its rating in centiStokes. This measure is vastly more accurate than "weight."

http://www.peterverdone.com/archive/lowspeed.htm

http://www.peterverdone.com/archive/images/content/motorcycle/PVD-ISO-Viscosity-Data.gif

Perhaps, most important (and biggest gain) with forks is to be certain your springs and preload reflect your rider weight and riding style. Factory springs are notoriously soft. Springs are also fairly inexpensive and super-easy to change during the oil service. I used Traxxion Dynamics to spec my springs and preload spacers and they are spot-on.

[audiomick]

Not quite on topic, but related: mine has a blown fork seal. Not just a drip, it lost (apparently) the entire contents of the left fork leg on the ground overnight after the last time I rode it. It has, according to the speedo, about 70,000 km on the clock.

I'm still tossing up about what to do. On the one hand, there is a place about 80 km away from here that is a "fork specialist", specifically Öhlins, but I gather he'll do any forks. On the other hand, the workshop that I use as needed has no doubt done forks, and can no doubt do a servicable job.

I was more or less happy with the fork's performance. As far as the "too soft" springs go, I currently weigh 65 kg, so I don't need particualrly hard forks.

So what should I do? Go to the effort to take the forks to the specialist, or just have them done by my "tame" mechanic? I do like to have things perfect, but on the other hand, I'm not going to be racing it or anything demanding like that.

I could have a go at it myself, but I don't think I'll find the time (it's already 6 months since the seal went), and I don't have the experience to evaluate the wear on the internal parts as to whether anything needs replacing.

I'd be interested in a "vote", what is the sensible thing to do, weighing cost and effort against advantages.

Edited March 13 by audiomick

[4corsa]

2 hours ago, docc said:

I learned (from this forum), early on, that lighter oil performs better in our forks, so I chose 5 "wt."

Then, I learned (from this forum) that 5 "weight" can vary widely between manufacturers and even between one manufacturer's different products. After taking in Peter Verdone's discourse, and published tables, I chose BelRay 5W High Performance fork oil based upon its rating in centiStokes. This measure is vastly more accurate than "weight."

http://www.peterverdone.com/archive/lowspeed.htm

http://www.peterverdone.com/archive/images/content/motorcycle/PVD-ISO-Viscosity-Data.gif

Perhaps, most important (and biggest gain) with forks is to be certain your springs and preload reflect your rider weight and riding style. Factory springs are notoriously soft. Springs are also fairly inexpensive and super-easy to change during the oil service. I used Traxxion Dynamics to spec my springs and preload spacers and they are spot-on.

Thank you docc, and how do you feel about the results? Did you notice any difference - are your forks more compliant or firmer?  Will you use the same Belray 5W?  

Just now reading in Guzziology p.572 "Starting in the Piaggio Era" owner's handbook call for either a viscosity of Fork 5W or Fork 20W. I'd recommend you start with 5W and I can't imagine going heavier than 10W unless you're trying to create damping where there isn't any in drum-brake loop-frame forks".

[4corsa]

...also beginning to better understand your choice for Belray 5W. According to Verdone, "most cartridge type forks use a viscosity of 16 cSt@40°C". Not sure what that's based on, but according to Belray's website, the 5W has a viscosity rating of 19.1 cSt@40°C. What's interesting to me is going to just 7W increases the viscosity all the way to 32.4 cSt@40°C, and 10W only slightly more to 34.9.

[docc]

1 hour ago, 4corsa said:

Thank you docc, and how do you feel about the results? Did you notice any difference - are your forks more compliant or firmer?  Will you use the same Belray 5W?  

Just now reading in Guzziology p.572 "Starting in the Piaggio Era" owner's handbook call for either a viscosity of Fork 5W or Fork 20W. I'd recommend you start with 5W and I can't imagine going heavier than 10W unless you're trying to create damping where there isn't any in drum-brake loop-frame forks".

Yes, indeed the more accurate cSt measure varies dramatically with the "weights" of common fork oils.

I am extremely pleased with my suspension set-up (YMMV). Yes, my target cSt is about 19.x while the typical "7wt" pushes into the 30s.

The 19.x gives me much more compliance and responsiveness from these forks. Again, I changed my springs, raised the forks in the triple trees 5mm, adjusted my tire pressures 35psi front/ 40psi rear (with selected tires/sizes for my rim widths), and changed the rear shock/spring rate/preload.

[4corsa]

14 hours ago, audiomick said:

Not quite on topic, but related: mine has a blown fork seal. Not just a drip, it lost (apparently) the entire contents of the left fork leg on the ground overnight after the last time I rode it. It has, according to the speedo, about 70,000 km on the clock.

I'm still tossing up about what to do. On the one hand, there is a place about 80 km away from here that is a "fork specialist", specifically Öhlins, but I gather he'll do any forks. On the other hand, the workshop that I use as needed has no doubt done forks, and can no doubt do a servicable job.

I was more or less happy with the fork's performance. As far as the "too soft" springs go, I currently weigh 65 kg, so I don't need particualrly hard forks.

So what should I do? Go to the effort to take the forks to the specialist, or just have them done by my "tame" mechanic? I do like to have things perfect, but on the other hand, I'm not going to be racing it or anything demanding like that.

I could have a go at it myself, but I don't think I'll find the time (it's already 6 months since the seal went), and I don't have the experience to evaluate the wear on the internal parts as to whether anything needs replacing.

I'd be interested in a "vote", what is the sensible thing to do, weighing cost and effort against advantages.

When you refer to "fork specialist (Ohlins) would you per chance be speaking of Markbilt near NJMP? If so, he is the GOAT, and top Ohlins service center in the northeast. He prepped all my track bike suspensions, and upgraded the valves / cartridges on most. The improvement was always very significant.  If you're planning to keep your bike for a while, its worth going to an Ohlins service center, and yes, they typically work on non-Ohlins suspension. Only issue may be that they are very busy this time of year prepping race bikes for the season.

[audiomick]

41 minutes ago, 4corsa said:

... Markbilt...

No. This place

https://öhlins-gera.de/de

which is here

https://www.openstreetmap.org/way/208123602#map=18/50.880637/12.166849

Not really close to New Jersey...

It's become a bit difficult here. There were two places with a good reputation. I had my rear shock done at one of them, but they have closed down. At the other place, the owner apparently has health issues and can't say when (or if...) he will be back to normal operations.

I turned up Motoradtke myself, but so far haven't had any comments back in the various forums about the quality of the work. I assume, though, if he can stay as official Öhlins partner, then he probably is at least competent.

Edited March 13 by audiomick

[4corsa]

On 3/12/2025 at 10:50 PM, docc said:

Yes, indeed the more accurate cSt measure varies dramatically with the "weights" of common fork oils.

I am extremely pleased with my suspension set-up (YMMV). Yes, my target cSt is about 19.x while the typical "7wt" pushes into the 30s.

The 19.x gives me much more compliance and responsiveness from these forks. Again, I changed my springs, raised the forks in the triple trees 5mm, adjusted my tire pressures 35psi front/ 40psi rear (with selected tires/sizes for my rim widths), and changed the rear shock/spring rate/preload.

Out of curiosity, did you go with firmer or softer springs? 

[docc]

1 hour ago, 4corsa said:

Out of curiosity, did you go with firmer or softer springs? 

Firmer. Also firmer on the shock spring. I have all of those details, but not where I am this weekend.

Traxxion Dynamics spec'd the springs and preload spacer length for my weight and "riding style."  It came out perfectly.

FWIW, I'm about 185-195 pounds in full gear, ride on the sporty side and wanted a 30mm rider sag, about 30%. (My target sag for the rear was 25%).

[audiomick]

28 minutes ago, docc said:

... 185-195 pounds in full gear,...

So about 86 kg in proper units.

I'm around 65 kg without the gear, so maybe 75 kg all kitted up. Do you reckon I'd be right with the standard springs, assuming they are still ok?

I'm inclined to think I would be. The front end felt alright the last time I rode it. I had put the pre-load back to the "default" settings from the user's manual.

[4corsa]

Lol - I was hoping you'd take the hint and supply your weight and save me the awkward task of asking 😅.  Thanks for all the info, docc!

Edited March 14 by 4corsa

[audiomick]

4 minutes ago, audiomick said:

... so maybe 75 kg all kitted up...

A quick check with an armful of gear on the bathroom scales confirms that this is about right. So about 165 pounds with all the gear.

[docc]

18 minutes ago, audiomick said:

So about 86 kg in proper units.

I'm around 65 kg without the gear, so maybe 75 kg all kitted up. Do you reckon I'd be right with the standard springs, assuming they are still ok?

I'm inclined to think I would be. The front end felt alright the last time I rode it. I had put the pre-load back to the "default" settings from the user's manual.

Right, so, about 13 or 14 stone. In proper units. 

12 minutes ago, audiomick said:

A quick check with an armful of gear on the bathroom scales confirms that this is about right. So about 165 pounds with all the gear.

Back in the day, rumor had that the wiry, Italian test riders weighed just that.   Yet, I also know an industry insider that told me the manufacturers set bikes up soft for "showroom feel." Except Ducati.

The only way to assess your spring rate applicability is to check your "sags."   Sags too far? Spring's too soft. Generally speaking (very generally), 35% of the suspension travel is soft (some riders like it that comfy), while 25% sag is considered "sporty." 30% is a common compromise.  

[audiomick]

17 minutes ago, docc said:

...

The only way to assess your spring rate applicability is to check your "sags." ...

Yes. Without getting into "sag" and "over 60 years old", I reckon I can get my garage "flat-mate" to help me have a look at how much the suspension on the bike sags when I sit on it.