What the fork??

[Daddy Dom]

Hi all,
I'm here on the other side of the world from NLM with my new progressive fork springs, and I have some questions. I should call them, but they're not up yet and some of you probably are.
First, it's a 1983 K Sport with Marzocchi forks. The old springs are 46cm long, with a metal sheath 25cm long over the top half and above that is an 8.5cm spacer. (Total length, 54.5cm.) The new springs are 54cm long and appreciably wider, so the sheath does not fit and is therefore - I presume - out of the picture. Here's the tricky part (to me).
If I use the 8.5cm spacer, I cannot physically compress the springs enough to get the nut into the threads. Without the spacer the new springs fit almost to the bottom of the nut and once tightened, everything feels pretty slack. The lack of tension/general springiness when pushing down on the handlebars tells me I may need the spacer, making my effective spring length 62.5cm, so what's the trick?
Cheers,
DD

[spub]

Have on order a set of progressive rate springs from NLM for my 1975 Sport myself, so I am going to be interested in replies. My guess from installing new dual rate springs on my bevel ducatis is that the new springs will be firmer, so you will not need as long a spacer. On my bevels I used a shorter spacer on one bike and did not need any spacer on the other, compared to the stock springs (which had a smaller diameter) and the spacers used with the stock springs. Also, make sure you have all the weight off the front wheel, I place a jack under the bike to make sure the front wheel is off the ground, so that I can insert the spacer. You need another person when doing this to keep the bike steady.

[EVguru]

From the RaceTech website;

Q: What is "Race Sag" (Static Sag)?
A: Static Sag or Race Sag is the amount the bike compresses from fully extended, with the rider on board.

Here's how to measure it.

First extend the forks or shock completely and measure from the wiper to the bottom of the triple clamp on forks or from the axle to a vertical reference point on the chassis. This is L1.
Take the bike off the stand, put the rider on board in riding position. Get an assistant to balance the bike or have the rider hold onto something, comress the suspension about 25 mm (1") and let it extend very slowly (slowly is the critical term). Where it stops, measure the distance between the wiper and the bottom of the triple clamp or the axle and the reference point on the chassis again. Do not bounce. This is L2. (If there were no friction in the seals the bike would come up a little further.)
Next lift up on the suspension and let it drop very slowly. Where it stops measure again. Do not bounce. This is L3. The reason L2 and L3 are different is due to stiction or drag in the seals and bushings. (If there were no friction in the seals or the linkage the bike would drop a little further.)
Half way between L1 and L2 is where it would come to rest with no friction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true Static Sag.
Static Sag = L1 - (L3 L2)/2
To adjust Static Sag make longer or shorter preload spacers or use the preload adjusters, if available.
It is important to note that there are no magic Sag numbers. However here are some guidelines to use as starting points.

Front % sag, mm sag, Rear % sag, Rear mm sag, Rear Free Sag mm

Street Bikes 28-33%, 30-35mm, 28-33%, 30-35mm, 0-5mm
Road Race Bikes 23-27%, 25-30mm, 23-27%, 25-30mm, 0-5mm

[Jem]

I fitted progressive springs from NLM and have no problem with them - the ride is softer at small loads then firms up with higher loadings. It was certainly at least as good at the MRC track day last year.
The springs fitted without the 8.5cm spacer and just a slight bit of compression (one hand enough to push down and turn the nut).

I can't recall but how much compression did the old spring and spacer need to fit? I don't think it was much.

I suggest take it for a ride and see how it feels.

Do read the instructions carefully when refilling the fork oil. I overdid it for some reason and ended up syphoning oil out - messy!

[Daddy Dom]

Hi Paul, and thanks for your endless patience in schooling many of us on the finer (and blunter) points of looking after a Morini.
I had actually found that page from an earlier post but I'm at a disadvantage in that I am not an engineer and I'm largely numerically dyslexic. Even though I have endless envy and admiration for those who can, I can't make any sense of those formulae. My eyes glaze over. (I'm actually quite a confident mechanic, but more with logic and feel.)
What I can use is descriptive advice like, "if the forks feel looser than before with the new springs you may need to consider cutting the old spacer in half." or whatever the case may be. Sorry to be a neanderthal ...

[Brubru]

I also converted to the progressive springs from NLM a few years ago. Very similar experience to Jem's. I haven't placed the 8.5 cm spacers and it's really fine like that. I remember they were really easy to install, only little pressure was required to re-install the nut.

The difference with progressive springs is that they are definetely softer in the beginning of the compression, increasing the compfort, and then becoming ... well, progressively ... much harder than the standard ones under heavy breaking or bumps.

Like Jem wrote: try it, and you'll see!

Bruno

[EVguru]

It boils down to wanting about 1/3 of the total front suspension travel used with you sitting on the bike. Friction in the forks makes this hard to measure, which is why Race Tech use the compress and release and then lift and drop to get two measurements and then take the average of the two. The difference between the two measurements indicates how much friction there is in your suspension (ideally none) and if they're too far apart you should be looking for bent stanchions or twisted yokes or re-set the wheel spindle.

The original springs were probably chosen for a slim Italian youth, and are too light. Ideally you'd go to a suspension specialist (Hagon or Maxton for example) and have them supply springs matched to the weight of the bike and the rider and the intended use (off-road, road, trackday, race, etc.).

A progresive spring is a comprimise solution, both for the relatively crude damping and also variable rider weight. As you increase the pre-load, you not only raise the ride hight (aiming for the previously mention approx. 1/3 travel), but also make the spring stiffer. It's easy enough to make your own preload spacers. Plastic electrical conduit is often strong enough (the preload spacers on Darts are plastic tube).

[spub]

Getting a front fork right takes a lot of experimenting, since there are many variables: Pre-load, stiction, oil weight, volume and valving and type of spring. I have converted all of the Marzocchi forks on my other bikes to progressive wound springs, and on my bevels I found a neat billet replacement fork tube cap that has a built in pre-load adjuster. Wish I could find these for 35mm Marzocchi (my other bikes use 38s). My experience has been that I could set up my other bikes fine for street riding working with these variables. Whatever amount of preload I ended up with resulted from a balancing of all these factors. I guess I might be able to get it a bit better if I purchased springs custom tailored for my weight and the bikes weight, but on all my bikes I just used the springs that were provided, and the vendor did not get specific on these matters. That being said, the stock springs on most Italian bikes I have ridden are woefully underspec'd (for US use) as EV points out, and looking at the typical Italian vs. the typical American, I can see why. Adding pre-load helps address bottoming and diving issues, however as EV says it raises ride height in the front (which may or may not be desireable) and makes for a firmer, and sometimes harsher, ride. The goal of progressive wound springs is to retain a certain plushness to soak up minor road imperfections, but to increase stiffness when larger imperfections are encountered or a braking load is applied. They are an improvement over stock but since they are being incorporated into a springing/damping system the net result of the whole is not dependent solely on the springs themselves, but on how you balanced all of these factors.

[Daddy Dom]

Hi All, and thanks for your patience. Luckily, common sense won out and I went out for a quick blatt round a few blocks. Of course, it was just going to be one block, but that's a Morini for you.
I was cautious precisely because there are so many variables and experience has shown me that it's extremely rare for a replacement part to "just slot in", especially with my model K.

The original springs were probably chosen for a slim Italian youth

I loved this insight, Paul, and as I weigh 61kg (or 9.605 855 709 5 stone) and eat a lot of Italian food clearly have nothing to worry about with rider-weight. I seem to have that magic fork 1/3 travel, too.

And, spub, your comments were in fact exactly what I found.

The goal of progressive wound springs is to retain a certain plushness to soak up minor road imperfections, but to increase stiffness when larger imperfections are encountered or a braking load is applied.

So now we can all get some sleep! Thanks again.
Daddy Dom

[spub]

installed the progressive wound springs I got from NLM last week. Installed new seals and used 200cc of 10wt fork oil and no spacer as a starting point. Found a bit too much sag, and a bit too much stiction. Loosened the bolts clamping the stanchions and played the positioning until stiction reduced, and then added a 3mm spacer to each leg. This improved matters significantly, and the set up appears pretty close.

Fork diving much reduced, heaving braking upsets the ride much less, and bike feels much more secure in corners, especially if braking just prior. Will experiment with oil volume/air gap and oil weight, but this appears close.

A very worthwhile investment of time and money, and the installation was very straightforward. For reference purposes I am 5'10" and 190lbs, and the bike is a Sport with clip ons.