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Fork Compression and Rebound manual typo?


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When in doubt look at the shop manual. Looks like you have an earlier owners manual. The transition of components for Guzzi isn't a hard line and so neither will be the owners manuals. Ciao

Before doing any major work or installing a valve or cartridge kit, why not set the sag and play with the adjusters?  Perhaps you might set the adjusters independently as well as tandem?  Get a feel f

Some front forks have rebound adjustment at the top and compression adjustment at the bottom. The Italian Marzocchi's are a little unusual in that they often have rebound in one leg and compression in

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I’ve done more measurements since I backed out the preload on both forks all the way. The rebound is mostly backed out on each fork too.  

The rear has 34mm rider sag (most of that is from (27mm) rider getting on and only maybe 7mm if that was static sag from weight of bike standing. 
but the front is the other way around. 
It only drops another 7mm when I sit on it in full gear but when I get off and lift almost all the weight off the wheel to check for static sag it rises about 26mm. So the static is 26mm and the rider ads only 7mm to make the rider sag 33mm. 
I was told to aim for 30-35mm in the rear for preload sag and 35-40mm In the front. So ideally a little bit more sag up front but I’m relieved to see that the static sag was so large considering the minimal movement when I sat on it. The rear is the opposite. But both add up to the same. 
I put cable ties on the front forks and with normal riding on twisty roads I used all but the last 25-30mm of travel. When I did a harsh stop to test if it bottomed out it still had about 15mm left. 
I think I can live with these settings. Tomorrow my mechanic is going to change the Old sae 10 fork oil with sae 5 oil to see if that helps soften the ride at all. If it does too much I have all the preload yet to add as now it’s backed almost completely out (same with rebound). And I can always go back to sae 10 or 7. 
Anyone try lighter fork oils than the 10 in the manual?

Thanks guys
 

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1 hour ago, HantsV11LeMans said:

I’ve done more measurements since I backed out the preload on both forks all the way. The rebound is mostly backed out on each fork too.  

The rear has 34mm rider sag (most of that is from (27mm) rider getting on and only maybe 7mm if that was static sag from weight of bike standing. 
but the front is the other way around. 
It only drops another 7mm when I sit on it in full gear but when I get off and lift almost all the weight off the wheel to check for static sag it rises about 26mm. So the static is 26mm and the rider ads only 7mm to make the rider sag 33mm. 
I was told to aim for 30-35mm in the rear for preload sag and 35-40mm In the front. So ideally a little bit more sag up front but I’m relieved to see that the static sag was so large considering the minimal movement when I sat on it. The rear is the opposite. But both add up to the same. 
I put cable ties on the front forks and with normal riding on twisty roads I used all but the last 25-30mm of travel. When I did a harsh stop to test if it bottomed out it still had about 15mm left. 
I think I can live with these settings. Tomorrow my mechanic is going to change the Old sae 10 fork oil with sae 5 oil to see if that helps soften the ride at all. If it does too much I have all the preload yet to add as now it’s backed almost completely out (same with rebound). And I can always go back to sae 10 or 7. 
Anyone try lighter fork oils than the 10 in the manual?

Thanks guys
 

Yep. See post above about BelRay 5 wt I've been using. Realize some manufacturer's 10 wt is lighter than others' 5 wt. Look at the Peter Verdone Design chart of viscosities in cST@40ºC and @100ºC for more accurate comparisons.

Verdone has some very insightful observations about adjusting damping in these fork systems. Worth the read.

Happy to see you getting her sorted! :thumbsup::luigi::race:

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13 minutes ago, docc said:

Yep. See post above about BelRay 5 wt I've been using. Realize some manufacturer's 10 wt is lighter than others' 5 wt. Look at the Peter Verdone Design chart of viscosities in cST@40ºC and @100ºC for more accurate comparisons.

Verdone has some very insightful observations about adjusting damping in these fork systems. Worth the read.

Happy to see you getting her sorted! :thumbsup::luigi::race:

Remember my advice from a while back here docc. Do a viscosity test of your original fork oil BEFORE you change it out so you know what the starting point is. take a small syringe without the needle and plunger and fill it to a level then let it drip into a container while timing the drips. Then take your oil of choice in whatever weight you decide and do the same so you verify that what you're putting in is actually the way you want to go. Who knows what weight oil is in the forks and importantly all "weights" aren't necessarily the same. Can save a lot of messing about and expense.

Ciao

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Just now, Lucky Phil said:

Remember my advice from a while back here docc. Do a viscosity test of your original fork oil BEFORE you change it out so you know what the starting point is. take a small syringe without the needle and plunger and fill it to a level then let it drip into a container while timing the drips. Then take your oil of choice in whatever weight you decide and do the same so you verify that what you're putting in is actually the way you want to go. Who knows what weight oil is in the forks and importantly all brands of 5,10 etc "weights" aren't necessarily the same. Can save a lot of messing about and expense.

Ciao

 

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Good points, as always.

One trouble with "testing" the oil coming out is that it could be rather used up (viscosity degraded/sheared) and no real indicator of what it was when fresh.

+1, again, that SAE "weights" are all over the place and that some fork oils retain more viscosity when hot than others (hence the cSt measures at both 40ºC and 100ºC.

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6 minutes ago, docc said:

Good points, as always.

One trouble with "testing" the oil coming out is that it could be rather used up (viscosity degraded/sheared) and no real indicator of what it was when fresh.

+1, again, that SAE "weights" are all over the place and that some fork oils retain more viscosity when hot than others (hence the cSt measures at both 40ºC and 100ºC.

Fork oil doesn't change it's viscosity like engine oil docc, it's life is too easy to worry about that and it doesnt have any viscosity improvers in it, it just a straigh weight oil. It may be a little more viscous due to particulate contamination but if you take it from the top and let it settle for a few hours then it wont be affected.

Fork oil will never see 100 deg C docc so that's not an issue and depending on the base weight variations then there will be a Cst variation due to temp changes as well.

Ciao 

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5 hours ago, HantsV11LeMans said:

Thanks Footgoose, did that Newer manual say how much oil the forks take? 
My older manual says 0.84 litres for Marzocchi (sae 10) shock absorbers 

mine says 0.870

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30 minutes ago, footgoose said:

mine says 0.870

This is for both forks? I just filled my early Marzocchi (less volume) to a 110mm air gap (luftkammer) with 330 ml per side. My Owner Manual says 400 ml "each leg."

These are the 1999-2001 forks on the early Sports. But may be some indication that the capacity may not be best filled completely to the maximum . . .

 

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1 hour ago, docc said:

This is for both forks? I just filled my early Marzocchi (less volume) to a 110mm air gap (luftkammer) with 330 ml per side. My Owner Manual says 400 ml "each leg."

These are the 1999-2001 forks on the early Sports. But may be some indication that the capacity may not be best filled completely to the maximum . . .

 

Most likely docc. says "total amount needed" 0.870li -- that would make it 435ml per side. idk maybe start with 400 and then measure? who has a stat on this?

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7 hours ago, footgoose said:

Most likely docc. says "total amount needed" 0.870li -- that would make it 435ml per side. idk maybe start with 400 and then measure? who has a stat on this?

Thanks Docc and Footgoose and to all those who replied earlier. 
I’ve decided to go with the recommended sae 10 since I don’t know what was put in or how much if they ever touched the forks. It may be 15 years old. 
I have almost enough sag up front and I’m using plenty of travel so I won’t deviate from recommended until I know I have  the correct weight (10)at the right quantity(.870) 
Start with 400 per side as you said and look at air gap. 
I’ll let you know exactly how much oil goes in and how much air gap and how it rides afterwards. 

You all have been incredibly helpful. 
Glad I joined. Now I’m going to search topics for rear sets or lower pegs. I have long legs and love this bike for the first hour or two. Like it until the 4th hour, but I rode from UK to Mandello del Lario last month and the long days on motorways killed my knees. 
Seat height is too close to peg height for my legs. I’ll look on this forum for suggestions. 
cheers guys
 

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