Forkupgrade: FAC + progressive springs = bottom out ?

[StubkierDK]

Hey

I need some help from the experts - and normally there more than one online here  :bike

As the subject indicates I have "upgraded" the suspension on my T3. There where some small specks of rust on the front fork-tubes and the seal was leaking so I saw it as a good time to renovate/upgrade the forks.

I ordered the following items:
FAC dampers
http://www.hmb-guzzi.de/shop/Chassis-and-Frame/Front-Fork-55/Shock-absorbers-56/Fork-Damper-set-FAC-T3--LM-2--LM-3-etc-.html
WIRTH4040 progressive springs
http://www.hmb-guzzi.de/shop/Chassis-and-Frame/Front-Fork-55/Fork-Springs-158/
And some new fork tubes
http://www.hmb-guzzi.de/shop/Chassis-and-Frame/Front-Fork-55/Upper-Fork-Tubes-163/Fork-Tube-35mm-T3--SP--LM-2--LM-3-etc-.html

The old springs where clearly shorter than the new ones - and since they had the same model number they where up for at change. I addition the damper units also had rust specks and the pistonrod did not move smoothly.

However, now, if I brake hard or push really hard down on the handle bars the forks bottom out with a rather uncomfortable clonk sound. Under normal riding conditions there is no problems and it holds the line through corners (near) perfect. I never had that problem before - so currently i does not seem to be much of an upgrade.

When installing the new dampers I reused the damper rods (item 27 on page 110 in the Haynes manual). Left the locknut in the same position = threaded all the way down towards the actual damper.

Filled the forks with 200ml of fork oil and added 0.2 bar the dampers -> as instructed by my local Guzzi Workshop.

What have done wrong? Or do I simply need to add spacers to add pre-load to account for my 100kg (220punds or 15 stones for the non metric riders)

Hoping that you have some inputs

BR Simon

[Antietam Classic Cycle]

Filled the forks with 200ml of fork oil and added 0.2 bar the dampers -> as instructed by my local Guzzi Workshop.

Each fork leg should only have 60 cc of oil (atf) in them. General consensus is no air pressure. 

[charlie b]

Yes, they will bottom out  :(  Pic are from my T5 after hitting a pothole.  The one bushing bottomed hard enough to jam in place.  FAC dampers and Wirth progressives.  Note that the bottoming out is when the spring is fully compressed.  Also, the spring is almost fully compressed at that point so adding preload won't help a whole lot.

FWIW, I can bottom mine out over a speed bump or into many parking lot 'ramps'.

[Antietam Classic Cycle]

Yes, they will bottom out  :(  Pic are from my T5 after hitting a pothole.  The one bushing bottomed hard enough to jam in place.  FAC dampers and Wirth progressives.  Note that the bottoming out is when the spring is fully compressed.  Also, the spring is almost fully compressed at that point so adding preload won't help a whole lot.

FWIW, I can bottom mine out over a speed bump or into many parking lot 'ramps'.

What's the bushing between the spring and damper? Not an original Guzzi piece AFAIK, never seen one in any Guzzi fork I've had apart. Looks like it's jammed onto the locknut? Easy enough to fix - don't install that bushing.

I also reuse the original lock nut which is 11 mm hex vs. 13 mm for the one supplied with the FAC dampers. The smaller nut is much easier for the springs to slide over.

[StubkierDK]

Each fork leg should only have 60 cc of oil (atf) in them. General consensus is no air pressure. 

Thanks for the feedback - but should'nt more oil and higher pressure make the forks harder and not softer?

Yes, they will bottom out...  :
FWIW, I can bottom mine out over a speed bump or into many parking lot 'ramps'.

So it is a feature and not a bug ? Hmm guess I should have read some more information before I placed the order ;)

[StubkierDK]

What's the bushing between the spring and damper? Not an original Guzzi piece AFAIK, never seen one in any Guzzi fork I've had apart. Looks like it's jammed onto the locknut? Easy enough to fix - don't install that bushing.

I also reuse the original lock nut which is 11 mm hex vs. 13 mm for the one supplied with the FAC dampers. The smaller nut is much easier for the springs to slide over.

Just to advoid any misunderstandings - the pictures are not of mine dampers. The ones I have installed does not have the spacer on the locknot.

[yackee]

I did this upgrade to my T3 and have not had any issues.

[Moto]

I did this upgrade to my T3 and have not had any issues.

:+1
and  :+1 on 15 stone, too!

[charlie b]

The bushings came with the bike.  I reinstalled when I put in the FAC's.  Seemed to fit like it belonged there.  I just figured it came with the springs.

Next time I have them out will remove them.

PS after looking at the parts diagrams it looks like the PO kept the spacer between the two original springs and put it between the springs and shock body.

PPS Charlie, that G5 brake master cylinder I got from you is working great.  Thanks again.

[StubkierDK]

:+1
and  :+1 on 15 stone, too!

Hmm it sounds like i need to inspect/disasamble the forks.

[Stevex]

I've recently rebuilt my forks; I'd also decided to go down the FAC route but after advice, decided to re oil my original dampers as they were still oil tight. The black 'water' that came out, I replaced with quality 5w oil. I've also replaced my original LM2 fairing with an Airtech repo and it's saved a shed load of weight over the forks, so I stayed with the original springs. The springs were found to be about 15mm shorter than standard, which I put down to 35 years of use, so I just made up 15mm spacers to put them back to original (they are the 2 piece springs).
There should be a thin plastic spacer between the bottom of the damper and the top of the spring; otherwise the spring will just wear through the damper. The oil (ATF), is purely used as a lubricant, as the damping is carried out by the FAC cartridges.
Surprising to hear that the Wirth's compress so easily, especially as they're progressive.
Are the FACs re-fillable, is it possible they've not got enough oil in them?

That picture of Charlie b's FAC dampers looks as if it's the springs that have caught on the joining nut; that spacer doesn't look far enough down the damper rod to be caught on the nut.

[charlie b]

It was the Al spacer that was hung up, and not on the threads (there was some smooth space above where it was jammed).  It was just jammed cockeyed.

My old ones were pretty bad.  One had no oil in it at all and the other was really nasty stuff.  I considered the price of the FAC's cheap compared to the work of rebuilding the old ones.

I also have the added weight of most of an SPIII fairing on the front.  A few pounds heavier than stock.  But, it used to bottom out even before I put that or the FAC's on the bike.

I am just more careful now when going over bumps  ;)

PS and yes, when it bottoms out it sounds like the oil pan hits something.  Not a pleasant sound.

[blackcat]

I had FAC's in my CX and I probably ruined them from too much air. Anyway, when I went to order another pair, MG Cycle had an old set of Bitubo's which people seem to dislike but I took the chance with a set of Wirth springs. There is no way I can bottom those things out. Maybe I acquired the only good pair made by Bitubo, but I have no complaints.

[StubkierDK]

....
Are the FACs re-fillable, is it possible they've not got enough oil in them?
....

So you are thinking that a pair of brand new dampers needs to refilled with oil ? I migth be worth a shot. No mater what the forks will be taken apart this weekend.

[Antietam Classic Cycle]

Are the FACs re-fillable, is it possible they've not got enough oil in them?

So you are thinking that a pair of brand new dampers needs to refilled with oil ? I migth be worth a shot. No mater what the forks will be taken apart this weekend.

If the FACs have damping for the entire stroke (easy to check by hand), no "dead" spots anywhere, then they have enough oil in them. I've installed six sets of them with Wirth springs (just did a Le Mans III last week) and have had zero issues.

[Stevex]

So you are thinking that a pair of brand new dampers needs to refilled with oil ?

Just throwing it out there after re filling mine and noticing what they were like before they'd been properly filled.
Still not sure they are even re fillable, if so, it might be worth trying a heavier weight oil.
I couldn't ride with front suspension that regularly bottomed out unless treated with kid gloves; I'd have to find the problem or another solution.
Can't say I've ever heard of FAC units / Wirth springs doing this before this reading this thread; in fact some owners have reported that the Wirth springs were so hard after installation, they took a couple of thousand miles to 'bed in'.

[StubkierDK]

Update

Thanks for all of your feedback. I have now dismantle the front forks and in the process I have taken a lot of pictures. Lets get started  :pop

The first picture is of the left fork leg - it has just been removed from the triple tree clamps.



The next ones show the maximal travel of the fork tube

The measurement is roughly 50 mm from the dust cap. The range is the same on the right leg.

Next the oil is drained from the leg - this is with 1 week of riding = 350KM

I smells like new oil - but looks rather dirty.

Next the spring, damper and upper tubes are removed.

The photo shows the length of the spring which is protruding from the upper tube (ca 85 mm). The spring is mounted with the large winding at the bottom.

The spring is removed and the location of the bolt on the damper rods. At this stage I tested the function of the dampers and both of them operates 100% smoothly in both directions.



Draining the oil from the other legs did not when as smoothly as one could hope  ???:

It seemed like there was a small plug of dirt which had to pushed out before the oil could be drained.  Besides the oil removal process the main (only) difference between the two fork legs where the missing/added plastic bushing in the right leg:

I am guessing that the bushing is missing on the left leg. So I will add one when assembling the shocks again.

The pictures shows the resemble of the right leg - if you see anything which is out of order please let me know.







The final pictures shows the travel of the newly assembled shock 90 mm.

There is more travel - but I am still able to compress the shock fully just by leaning my body and adding weight.

Hope that some manged to get through all of the pictures and can see if everything is done right ?

As a side note the pressure of both the legs where still 0.2 bar and when the drain screw where removed a clear hissing sound could be heard.

[redrider90]

I rebuilt my 90 Mille with new Bitubos and wirth progressives.
I had to preload the springs considerably when I installed them. It was a bitch to say the least because I choose the lazy route and did it on the bike. Never again but that said I had to compress the springs and 1" or more to get the clip in place to hold the spring in place. Mille uses ATF only for lube. 
I find even 2 up and loaded and I have to really come to a hard stop to compress the front end. Even then I am not sure I am bottomed out. I forgot what it looks like in there cause its been awhile.  But if you did not have to preload the spring before putting on the retaining clip then I gotta wonder if you have the correct springs.

[redrider90]

You said   " but I am still able to compress the shock fully just by leaning my body and adding weight.


Something is wrong. I can stand still and use the full force of my 6'5" frame with my front brake locked and cannot fully compress the front end.

[redrider90]

url]

The old springs where clearly shorter than the new ones - and since they had the same model number they where up for at change. I addition the damper units also had rust specks and the pistonrod did not move smoothly.

BR Simon

Why would they have the same model number? Wirth is an aftermarket product. Would it not have a different number on it not being a  Guzzi product?

[StubkierDK]

....I had to preload the springs considerably when I installed them. It was a bitch to say the least because I choose the lazy route and did it on the bike. Never again but that said I had to compress the springs and 1" or more to get the clip in place to hold the spring in place. Mille uses ATF only for lube.  ...

There is only a very small amount of pre-load in the springs. However it is more than the with the old springs.

You said   " but I am still able to compress the shock fully just by leaning my body and adding weight.
Something is wrong. I can stand still and use the full force of my 6'5" frame with my front brake locked and cannot fully compress the front end.

This is only with one fork leg. I have not assembled the left yet. But I am guessing that two forks will provide double the force.

Why would they have the same model number? Wirth is an aftermarket product. Would it not have a different number on it not being a  Guzzi product?

It is a bike from 1978 - i am guessing that the springs have been change more than once? It is the new spring on the top. If you look really close you can see that the springs have the same number.

[StubkierDK]

Both the legs are back on the bike - however the travel is now again reduced to 50mm  >:(. Both of legs had around 90mm of travel when tested alone.

Any clues to what is wrong?

BR Simon

[charlie b]

Is the front jacked up off the ground?

When on the center stand mine compress almost an inch.  Doesn't take much to do that.

[StubkierDK]

Is the front jacked up off the ground?

When on the center stand mine compress almost an inch.  Doesn't take much to do that.

In the words of Homer Simpson DO´H ! If it put up on the front jack the travel is 90mm :) So we are back to the start.

[charlie b]

When my fork collapsed I discovered how little weight it takes compress the front springs.  With only one spring working  I could easily lift the front wheel to almost fully compress the second spring.  Just the weight of the bike on one spring fully compressed it.

[Dick]

A few links and article for you. More out there. Hope it helps and good luck.

http://www.gostar-racing.com/club/motorcycle_suspension_set-up.htm
http://www.sportrider.com/suspension-setup-guide
http://www.strappe.com/suspension.html
 Suspension and Springs - Sag
What's all this ruckus about suspension these days? It seems everyone is clued in that suspension setup can be a key to riding fast and safely, but how do you do it? No matter what shock or fork you have, they all require proper adjustment to work to their maximum potential. Suspension tuning isn't rocket science, and if you follow step-by-step procedures you can make remarkable improvements in your bike's handling characteristics.

The first step to setting up any bike is to set the spring sag and determine if you have the correct-rate springs. Spring sag is the amount the springs compress between fully topped out and fully loaded with the rider on board in riding position. It is also referred to as static ride height or static sag. My company, Race Tech, 951.279.6655 has an advanced method of checking spring sag that I'll describe.

If you've ever measured sag before, you may have noticed that if you check it three or four times, you can get three or four times, you can get three or four different numbers without changed anything. We'll tell you why this occurs and how to handle it.

REAR END
Step 1: Extend the suspension completely by getting the wheel off the ground. It helps to have a few friends around. On bikes with sidestands the bike can usually be carefully rocked up on the stand to unload the suspension. Most race stands will not work because the suspension will still be loaded by resting on the swingarm rather than the wheel. Measure the distance from the axle vertically to some point on the chassis (metric figures are easiest and more precise; Figure 1). Mark this reference point because you'll need to refer to it again. This measurement is L1. If the measurement is not exactly vertical the sag numbers will be inaccurate (too low).

Step 2: Take the bike off the stand and put the rider on board in riding position. Have a third person balance the bike from the front. If accuracy is important to you, you must take friction of the linkage into account. This is where our procedure is different: We take two additional measurements. First, push down on the rear end about 25mm (1") and let it extend very slowly.

Where it stops, measure the distance between the axle and the mark on chassis again. If there were no drag in the linkage the bike would come up a little further. It's important that you do not bounce! This measurement is L2.

Step 3: Have your assistant lift up on the rear of the bike about 25mm and let it down very slowly. Where it stops, measure it. If there were no drag it would drop a little further. Remember, don't bounce! This measurement it L3.

Step 4: The spring sag is in the middle of these two measurements. In fact, if there were no drag in the linkage, L2 and L3 would be the same. To get the actual sag figure you find the midpoint by averaging the two numbers and subtracting them from the fully extended measurement L1: static spring sag = L1 -[(L2 + L3) / 2].

Step 5: Adjust the preload with whatever method applies to your bike. Spring collars are common, and some benefit from the use of special tools. In a pinch you can use a blunt chisel to unlock the collars and turn the main adjusting collar. If you have too much sag you need more preload; if you have too little sag you need less preload. For road race bikes, rear sag is typically 25 to 30mm. Street riders usually use 30 to 35mm. Bikes set up for the track are compromise when ridden on the street. The firmer settings commonly used on the tract are generally not recommended (or desirable) for road work.

You might notice the Sag Master measuring tool (available from Race Tech) in the pictures. It's a special tool made to assist you in measuring sag by allowing you to read sag directly without subtracting. It can also be used as a standard tape measure.

Measuring front-end sag is very similar to the rear. However, it' much more critical to take seal drag into account on the front end because it is more pronounced.

FRONT END
Step 1: Extend the fork completely and measure from the wiper (the dust seal atop the slider) to the bottom of the triple clamp (or lower fork casting on inverted forks; Figure 2). This measurement is L1.

Step 2: Take the bike off the sidestand, and put the rider on board in riding position. Get and assistant to balance the bike from the rear, then push down on the front end and let it extend very slowly.

Picture

Where it stops, measure the distance between the wiper and the bottom of the triple clamp again. Do not bounce. This measurement is L2.

Step 3: Lift up on the front end and let it drop very slowly. Where it stops, measure again. Don't bounce. This measurement is L3. Once again, L2 and L3 are different due to stiction or drag in the seals and bushings, which is particularly high for telescopic front ends.

Step 4: Just as with the front, halfway between L2 and L3 is where the sag would be with no drag or stiction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true spring sag: static spring sag = L1 - [l2 + l3) / 2].

Step 5: To adjust sag use the preload adjusters, if available, or vary the length of the preload spaces inside the fork.

Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm.

This method of checking sag and taking stiction into account also allows you to check the drag of the linkage and seals. It follows that the greater the difference between the measurements (pushing down and pulling up), the worse the stiction. A good linkage (rear sag) has less than 3mm (0.12") difference, and a bad one has more than 10mm (0.39"). Good forks have less than 15mm difference, and we've seen forks with more than 50mm. (Gee, I wonder why they're harsh?)

It's important to stress that there is no magic number. If you like the feel of the bike with less or more sag than these guidelines, great. Your personal sag and front-to-rear sag bias will depend on chassis geometry, track or road conditions, tire selection and rider weight and riding preference.

Using different sag front and rear will have huge effect on steering characteristics. More sag on the front or less sag on the rear will make the bike turn more slowly. Increasing sag will also decrease bottoming resistance, though spring rate has a bigger effect than sag. Racers often use less sag to keep the bike clearance, and since roadraces work greater than we see on the street, they require a stiffer setup. Of course, setting spring sag is only first step of dialing in your suspension, so stay tuned for future articles on spring rates and damping.

-Paul Thede

Magazine: Sport Rider
Issue : August 1995

[redrider90]

I am curious as to how the bike feels on one of those sections on the super slab where you have an lots of expansion joints  that seem to appear every 20 or 30 feet.
With my progressive springs on these areas are bothersome and jolt me as there is no compression in the front end. So it is like getting hit every time. At 70 mph it can be uncomfortable. On the stock springs I never felt those joints as the springs were so weak they absorbed even the slightest jolt.

[Dick]

I am curious as to how the bike feels on one of those sections on the super slab where you have an lots of expansion joints  that seem to appear every 20 or 30 feet.
With my progressive springs on these areas are bothersome and jolt me as there is no compression in the front end. So it is like getting hit every time. At 70 mph it can be uncomfortable. On the stock springs I never felt those joints as the springs were so weak they absorbed even the slightest jolt.

This article might help explain this, somewhat.

http://racetech.com/articles/CartridgeForks.htm

[charlie b]

We have a particularly bad spot like that on I-40 near my home.  The middle lane is bad enough I won't even drive my truck on that portion of the road.  The wheelbase and stiff suspension are enough to make it uncomfortable.

On the T5 with the progressive springs it isn't quite as bad as the truck, but, I also avoid that section of the highway with the bike.  (I also avoided that section with my Honda)

I cannot compare to stock springs since my bike had the progressives when I bought it.  Compared back to back with the Honda NT the T5 seemed a little more stiffly sprung over sharp bumps.

[mwrenn]

I am curious as to how the bike feels on one of those sections on the super slab where you have an lots of expansion joints  that seem to appear every 20 or 30 feet.
With my progressive springs on these areas are bothersome and jolt me as there is no compression in the front end. So it is like getting hit every time. At 70 mph it can be uncomfortable. On the stock springs I never felt those joints as the springs were so weak they absorbed even the slightest jolt.

I had the same problem with my V7C.  It has a mupo progressive spring kit with an emulator.  I started with 10W oil, but had too much dampening.  I wound up using Motorex 2.5 weight oil and worked great.  No bottoming, and perfect dampening.  I wanted to be able to abruptly compress the forks and release them.  They should go down, come back up, and then settle a few millimeters.