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-   -   Marzocchi 48mm CC - More learning (http://www.gasgasrider.org/forum/showthread.php?t=17386)

Jakobi 05-13-2014 04:18 AM

Marzocchi 48mm CC - More learning
 
Doing a bit of work on a friends forks and thought I'd take a few pictures along the way for anyone who's interested. Perhaps a little info on whats what, and I'll try and snap some more on the bleed procedure once the new parts arrive.

These forks had previously been worked on by someone else and I haven't been overly impressed with the lack of attention to detail. Never the less, these things happen.

Upon receiving the forks I gave them a through inspection. Dropped the dust seals and cleaned them a bit. Neither leg appeared to be leaking after this.

Compression and Rebound settings recorded, and PFP as well. When going through these noticed all clickers had been assembled without the correct range of 26 clicks. They all varied from 20-24. The PFP on one leg was considerably firmer to turn, and when backing it out proceeded to come out a full 6 turns where the other only came out 2.

I set the clickers back and PFP at 2.5 and rode the forks for a 120km loop to get a feel for how they were working. They felt very plush but also had that similar feeling that stock forks have. I can't describe it well but it feels like a lot of bleed. The forks rode quite well but I think they would definitely be better with an increase in spring (which we plan to do).

Jakobi 05-13-2014 04:23 AM

After the ride it was time to begin the servicing and pull down. Removed the forks and opened the outer leg and drained the oil.

Very low fluid volumes in the outers (well below the 300ml minimum spec). Only leg had around 225ml where the other had around 235ml. Oil was a bit contaminated. After draining the oil, placed the forks in the vice to undo the 19mm nut that holds the cartridge in the leg.

http://i575.photobucket.com/albums/s...psb290553a.jpg

http://i575.photobucket.com/albums/s...psd017ab94.jpg

One the nut is removed the cart will pull straight out the other end, and the spring will also come out at the same time.

http://i575.photobucket.com/albums/s...psfb089f1f.jpg

Jakobi 05-13-2014 04:32 AM

Pry the dust seal down and then remove the circlip that holds the oil seal in. I used the heat gun to warm up the outer leg to assist with removal, and then in a slide hammer action pull the upper and lower legs apart.

http://i575.photobucket.com/albums/s...ps5060c74a.jpg

Place all parts in order in a clean work area.

http://i575.photobucket.com/albums/s...ps2bf4e4d6.jpg

Next, mount the cartridge in the vice and remove the compression assembly using your tool. I took the time to crack them and make sure they'd undo while the fork was still on the bench as a whole.

http://i575.photobucket.com/albums/s...ps4e293782.jpg

As the comp assembly unthreads it will pop up a bit. I find stroking the shaft in will push the whole assembly up some more. You can then hold the comp adj and pull the shaft down and you will hear it pull some air into the forks. Each time you cycle it back up it will push the assembly out a bit more until it comes out. Be careful if pulling on it as it will 'pop' out.

Jakobi 05-13-2014 04:38 AM

Drain the oil from the cart and cycle the shaft to bleed the oil out.

http://i575.photobucket.com/albums/s...ps67a0eb46.jpg

At this stage while inspecting the comp assemblies I noticed the springs had been replaced from the stock 2.0kg/mm to 1.8kg/mm. The springs appear to be shorter allowing more area for the piston to float above its stops. I also picked up that one of the PFP adjusters had been cross threaded. Nice.

http://i575.photobucket.com/albums/s...ps0219f5d0.jpg

I managed to disassemble these and with some care was fortunate enough that they went back together as they should have. Corrected the length on the threads to get a full range of 26 clicks on both adjusters. Cleaned and lubricated both assemblies and now the PFP turns with nothing more than a socket in the palm of my hand. Much improved. Very noticable that there is quite a bit of free play in these springs though.

Now waiting on the replacement springs and seals. More to follow.

wence 05-13-2014 05:54 AM

Great write up and detail mate.
Interesting finds in there???
Mark

Fred1956 05-13-2014 10:21 AM

Awesome report Jake, waiting to hear of finished product....

Jakobi 05-13-2014 04:40 PM

Thanks Mark and Fred

The free play on the piston is concerning me a little. It should still bleed up ok but with the PFP backed out it will have a negative preload (ie the spring will be free to rattle around). Ideally (if I had a lathe), I'd machine up a spacer to get the spring back into spec where it is lightly preloaded with the PFP at 0 turns in (7mm freeplay, PFP out). This would give the most useful range of adjustment.

In saying that, the fork still performed quite well so in this instance I'll likely reassemble them as they were with fresh fluid, a heavier outer spring, and a set of SKF seals.

wa_ndro 05-13-2014 06:46 PM

awesome write up Jake.
Makes me want to pull mine apart right now :)
My 'tuner'- also the gasgas rep in perth - serviced my forks.
They came back with different clicker settings on both legs for comp and reb, and different PFP settings. Christ knows what the oil levels were.
Your posts will certainly make it easier for us DIY guys now
Cheers

n_green 05-13-2014 09:28 PM

Quote:

Originally Posted by Jakobi (Post 134200)
The free play on the piston is concerning me a little. It should still bleed up ok but with the PFP backed out it will have a negative preload (ie the spring will be free to rattle around). Ideally (if I had a lathe), I'd machine up a spacer to get the spring back into spec where it is lightly preloaded with the PFP at 0 turns in (7mm freeplay, PFP out). This would give the most useful range of adjustment.


My pfp spring is the same it has 5-7mm free play with pfp at fully out. I reckon that's the cause of the rattle I hear when the suspension is busy.

When my tuner was working on them the other day he mentioned his opinion of the adjustable preload is that it's a bit of a gimmick. Ie when fully wound on with say 10mm of preload you have effectively applied 20kg of force to the spring. However when the fork action does overcome that initial force the pfp spring will then compress at its usual rate of 2kg/mm or whatever it is. So really all winding the pfp in does is make the initial action of the fork firmer/harsher.

He revalved my forks with the pfp wound out and didn't seem fussed by the free play. If anything it should make the initial action plusher. However when it does start compressing the pfp spring could also cause a harsh spike?
Time will tell I have a big ride this weekend on the newly revalved forks.

Jakobi 05-13-2014 11:02 PM

When the fork is assembled and bled correctly, the piston will always settle into the same position in the cartridge. You can overfill the fork as much as you want, but the purging process will always see the piston at the same point (on the cusp of the bleed taper of the shaft), when the shaft is bottomed out.

Working backwards from here, the shaft must displace a given volume of oil as it enters the cartridge, which in turn passes through the base valve and continues to displace the floating piston. This point is 7mm from the ICS bottoming stop.

So if the spring has 0 preload with the PFP backed out, it will have around 7mm preload once bled. If the spring has 7mm free play, it will have 0 preload when installed. However, in the case above at around 10mm free play the spring will still have 3mm free play (negative preload). This leaves the springs foating around, and means that the ICS won't effectively 'push' the cartridge rod back to full extenstion. Pulling the rod out will still sink the piston into its position.

The biggest consideration with all this is that it has a massive effect on where you're PFP adjuster ends up in comparison to someone else, so much so that it could mean that me running my PFP fully in is comparable to someone else running theirs fully out. I don't think anyone would debate that a half a turn on the PFP is noticable, so thats some very large differences which also makes it hard to compare valving stacks and overall spring rates from one bike to the next.


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