1200Sport front suspension questions

[toma nova]

Noob here, still learning my wonderful 12S.

The left fork seal is leaking so that needs to be replaced. The oil is original, 2008 model with 6k miles, so I would replace the oil as well. I'm about 210lbs. with gear, rarely ride with a passenger and then only locally. Not a lot of twisties in TX so mostly aggressive sweepers (and tons of commuting miles). The big question ($$) is what to do with the internals.

I am mechanically inclined but with limited tools (no vise for clamping fork legs for example). I prefer to do my own work or at a minimum watch / help someone so I can learn and ensure that the work is done to my satisfaction. My least preferred is to drop something off at a shop and pick it up later. I don't mind buying new tools!

Can I replace seals (both?) in my garage? What about oil?

What grade / brand of oil?

What are the spring / preload / cartidge options? I just read Race-Tech's Suspension Bible but am still confused about how to improve these forks.

Thanks for all guidance,
Tom

 

[GTM®]

Tom, suspension is still a black art. Only years of knowledge and know-how will get good results. Reading a book won't get you anywhere quick, nor will trial and error. Best to leave it to the experts as to valving revisions, etc. If you want to invest in all of the proper tools to do something like replacing the fork seals, you'll need a vice with soft jaws to hold the fork legs, a seal puller, a metric allen socket for the bottom of the damper rods (and likely an impact wrench/driver), seal driver, along with a measuring device for the oil level. All of that likely isn't worth investing in for a job you'll do once or twice in the next ten years. As for valving, no one worth anything is going to tell you how to modify the shim stacks, once you figure out how to get everything apart. Knowledge = value. If you want a simple drop in kit like RaceTech or Traxxion, get ready to spend big $$$$, or find someone local willing to work with you (again $$$); There are a rare few that have successfully modified the 12S internals. Stock oil weight is 7.5, 10w is fine.
Best of luck on your journey, and keep us updated on how things go for you, or ping me direct e-mail if you want my help with them. I have successful experience with everything listed above. Minimally I have the seals in stock for far less then a dealer.

 

[PP-1753]

Quantity of oil makes a BIG difference. I think there was 5wt originally in mine. I replaced it with 7.5wt and used the correct amount as listed elsewhere here on GuzziTech (can't remember where exactly, but it's there all the same). Suspension is now firmer and feels firmly planted. I had to back off the compression from where I had it and the exact numbers too a while to dial in on the same piece of road, until I was happy.

 

[ghezzi]

If you have a local suspension guru you can work with, great! You can modify to your hearts content - and your walletts demise. My wallett has anorexia

The next best alternative is the Matris fork kit with new springs and oil. DIY or watch any mechanic.

 

[toma nova]

Uprgraded springs and spacers are in, new seals and dust covers are on, and new 10W oil has been dispensed.

As we all know, the service manual shows Breva 1100 forks and says to measure the air space with spring and spacer out. On our 12S, the spring and spacer must be installed onto the damping rod with he fork cap so the only way to get the right amount of oil in is to measure it by volume then pour it in.

I have the 400cc volume in the service manual for the B11, but I'm certain that I have read somewhere online that the 12S calls for 480cc. Does anyone have a reference for 1200Sport forks specifically?

I took several pictures during complete disassembly and servicing and I'll write everything up shortly - nothing out of the ordinary but may be a good reference for others.

Thanks,
Tom

 

[Rafael]

I took several pictures during complete disassembly and servicing and I'll write everything up shortly - nothing out of the ordinary but may be a good reference for others.

Tom, that would be helpful. I searched for S12 fork instructions a while back but wasn't able to find any. I have relatively new S12 forks on my B11 so I don't need to get into them anytime soon. I plan on getting heavier springs when I do.

 

[ohiorider]

I'm sorry to say this is all I could find. Every now and then, it appears that the tech writers at Guzzi simply do a cut and paste of specs from an older manual. Although the page in the pic came from the 1200 Sport manual, I'm guessing it shows the same volume of fork oil as the Breva 1100 manual. I'll look elsewhere in my notes and see if I can find anything different. I had my fork seals replaced at 18,000 miles, and I know I supplied the shop with volume info.



EDIT: The above came from the US Manual. The G Britain manual shows the same volume, as does the Owners' Manual that I found online.

 

[PP-1753]

I think I used 360cc of 7.5wt oil in mine. Long ride on the weekend and had to back off compression 4 clicks and rebound 2. Might be better with 5wt oil?

 

[toma nova]

I'm sorry to say this is all I could find. Every now and then, it appears that the tech writers at Guzzi simply do a cut and paste of specs from an older manual. Although the page in the pic came from the 1200 Sport manual, I'm guessing it shows the same volume of fork oil as the Breva 1100 manual. I'll look elsewhere in my notes and see if I can find anything different. I had my fork seals replaced at 18,000 miles, and I know I supplied the shop with volume info.



EDIT: The above came from the US Manual. The G Britain manual shows the same volume, as does the Owners' Manual that I found online.

Bob,

I used the same reference but I'm pretty sure I read 480cc somewhere. It's entirely possible I misread the service manual on the iPad in the garage, even though I have a pair of "cheaters" out there. BTW, 480cc comes up within sight of the top of the slider tube when it is compressed all the way in; this is not even close to the 120mm of airspace called for with the B11 forks - more like 20mm (plus the amount displaced by the spacer and spring, not a whole lot IMHO).

Since everything is back together (wheel, etc.), I'll try a gentle ride in the neighborhood - at the first sign of hydro-lock, I'll take the forks back off and remeasure to 400cc +/- a couple.

Tom

 

[kiwi dave]

I may be mistaken and offering myself up as a complete idiot, but doesn't the 1200 Sport have a cartridge for dampening? If this is the case, I would have thought that the quantity of oil, and to a large extent the viscosity is not critical, as it is there for lubrication only.

My $0.02c. Tell me I'm wrong, I love to learn about these things too.

 

[ohiorider]

If this were a BMW with Telelever instead of a Guzzi with telescopic shocks, yes. The oil would be for lube purposes only, since an automotive-type shock is used for spring, compression and rebound damping control.

However, whether a particular Guzzi comes with damper rod OR cartridge forks, both types depend on hydraulic oil passing through an opening (openings) to control compression and rebound damping. A hole in the damper rod controls the rate at which fluid can pass through it as the fork compresses and rebounds. A cartridge fork uses valving which opens at a specific pressure allowing fluid to pass. (I'm not good at explaining all that goes on in a cartridge fork.) There are devices (emulators) that contain a valve pack which can be inserted into damper rod type forks. These permit an inexpensive damper rod system to mimic a more expensive cartridge fork system. One brand requires drilling out the damper rod hole so that in effect, the damper rod is disabled. Another brand leaves the damper rod hole untouched, but requires using very light weight fork oil, so that it easily passes through the existing damper rod hole, effective removing the damper rod from the damping function.

Regardless of the damping mechanism used, the forks will react differently based on fluid level. Not because it changes how the fluid passes through the openings in the damping mechanism, but because the fork oil level determines how much of an air damper resides in the top of the fork. More air space (less fluid) cushier ride ... less air space (more fluid) not so cushy. Air compresses .... oil doesn't.

Go back to the 1980s. Recall, some of the Japanese bikes had Schrader valves on top of each fork leg. These were used to adjust air pressure in the top of the fork leg, which in turn affected ride firmness and fork dive.

So now I've probably really confused the issue!

 

[kiwi dave]

However, whether a particular Guzzi comes with damper rod OR cartridge forks, both types depend on hydraulic oil passing through an opening (openings) to control compression and rebound damping. A hole in the damper rod controls the rate at which fluid can pass through it as the fork compresses and rebounds. A cartridge fork uses valving which opens at a specific pressure allowing fluid to pass. (I'm not good at explaining all that goes on in a cartridge fork.) There are devices (emulators) that contain a valve pack which can be inserted into damper rod type forks. These permit an inexpensive damper rod system to mimic a more expensive cartridge fork system. One brand requires drilling out the damper rod hole so that in effect, the damper rod is disabled. Another brand leaves the damper rod hole untouched, but requires using very light weight fork oil, so that it easily passes through the existing damper rod hole, effective removing the damper rod from the damping function.!

Interesting. I thought a cartridge was self contained i,e, sealed. So in effect the actions are similar, and the advantage of the cartridge is that it offers more versatility?

Regardless of the damping mechanism used, the forks will react differently based on fluid level. Not because it changes how the fluid passes through the openings in the damping mechanism, but because the fork oil level determines how much of an air damper resides in the top of the fork. More air space (less fluid) cushier ride ... less air space (more fluid) not so cushy. Air compresses .... oil doesn't.

Go back to the 1980s. Recall, some of the Japanese bikes had Schrader valves on top of each fork leg. These were used to adjust air pressure in the top of the fork leg, which in turn affected ride firmness and fork dive.

I'm surprised that the air is allowed to compress to any great amount, i.e. it relies on air pressure to provide firmness and control fork dive. Would this not encourage oil to be forced out past the fork seal, or increase stiction, both undesirable side effects?

My California in the late 90's had Schrader valves on the top of each fork leg, and I believe I could add about 10 lbs/sq in air pressure. But later I learnt that this was to stop the oil frothing, and had nothing to do with firmness and fork dive. Certainly, I couldn't notice any difference. The rear shocks had a similar feature. But if this is such a good idea, why aren't these features present on modern bikes?

I'm learning as this discussion proceeds. Keep 'em coming!

 

[toma nova]

I have The Suspension Bible by Race Tech and recommend it - lots of schematics and easy-to-understand explanations. You won't become a tuning expert but I understand some of the changes I've made and what some other options are.

(I actually think that Norge and B11 owners are better suited for upgrades to their "primitive" damping rod forks than we are with cartridge forks that cannot be easily modified.)

Here are a couple of excerpts:

Damping Rod forks

Cartridge forks

Tom

 

[kiwi dave]

I have The Suspension Bible by Race Tech and recommend it - lots of schematics and easy-to-understand explanations. You won't become a tuning expert but I understand some of the changes I've made and what some other options are.

(I actually think that Norge and B11 owners are better suited for upgrades to their "primitive" damping rod forks than we are with cartridge forks that cannot be easily modified.)

Here are a couple of excerpts:

Damping Rod forks

Cartridge forks

Tom

Links didn't work, Tom. Can you check and resend, pls?

 

[ohiorider]

Kiwi Dave - you've exhausted the little I know (or think I know) off the top of my head about suspension. Maybe when we're able to open the links Tom referenced, we'll both be able to learn more. As far as I know:

- A fork described as a cartridge fork depends on valves (valve pack) to regulate the flow of hydraulic oil to control compression and rebound damping. It isn't actually an enclosed cartridge containing its own oil supply. EDIT: Thanks Todd - it's a 'shim stack', not a 'valve pack.'

- Re air in fork top end as a means to regulate fork action: I'm thinking back to my Yamaha Virago days (1983 750). My recollection is that Yamaha provided psi information for solo riding, and increased psi for riding with a passenger. Both the front forks and rear monoshock had this feature. I'm inclined to believe this was used instead of a spring preload adjustment, but, wow, that was 30 years ago! So, not certain about that.

More recently, I owned a Triumph Bonneville with inexpensive Kayaba damper rod front forks. There were no compression, rebound, or preload adjustments, and the forks were way soft as it came from the factory. We beefed them up typically with progressive springs, and heavier and more fork oil (measured in height from top of tube/with fork compressed and spring removed)

Some of us installed the Ricor Intiminators in combination with stock fork springs, to further improve the forks. I personally didn't get the results I wanted, so removed the Ricor units and returned to using progressive springs and heavier/more fork oil. Others were quite happy with them.

 

[GTM®]

Always best/smart to measure the oil drained as a general basis for refill, but note that some residual will be left behind (up to 10ml). The 12S cartridge forks are self contained with a shim stack, so it is not a sealed cartridge system, and does require a substantial oil level as noted above (Dave). :silly:

 

[toma nova]

Links updated.

 

[ohiorider]

Here's an inexpensive way I documented to set the fork oil level. I'm not certain how to dismantle 1200 Sport forks (cartridge with adjusters on the top caps), but on the Bonneville with simple damping rods and no adjusters on the caps, this worked fine. The reference to 'baster' means a turkey baster, like one would use while doing the Thanksgiving bird. Available at any decent grocery store.

On the Bonnie, I went from approx 140mm below the top to 120mm to firm things up a bit.

 

[GTM®]

Here's an inexpensive way I documented to set the fork oil level. I'm not certain how to dismantle 1200 Sport forks (cartridge with adjusters on the top caps)

This method is impossible on the 1200 forks because the cartridge/spring is one unit, bolted to the very bottom of the fork, and seals the fork assembly. It will certainly work for all other damper rod forks though.

 

[toma nova]

I have the 400cc volume in the service manual for the B11, but I'm certain that I have read somewhere online that the 12S calls for 480cc. Does anyone have a reference for 1200Sport forks specifically?

I'm not going (totally) crazy!

I found the reference to 480cc in the 1200 Sport 4V service manual.

However, that version of the SM still shows the B11 forks and calls for measuring the airspace - not an option on 12S forks since they're all bolted together before adding the oil.

So, I'd still like any guidance on which volume I should use. Trial and error is not a great option since removing the forks is time consuming.

Thanks for any wisdom,
Tom