Marzocchi 48mm Challenge!

[Jakobi]

Next time you have your forks apart and bleed them up, turn the cart upside down, cycle the rod once or twice, and tell me what happens.

I've been through the bleed procedure more times than I'd like to admit this arv. I'm lucky the missus is still talking to me!

I'll post up the method I used to get the best results, but even then, flipping the cartridge confirmed there was still some air hiding under the ICS piston. The good news is, if you flip it back over and cycle it as you would when initially filling it self bleeds and goes back to performing as it should. I've opened the cart after doing this and its not foamed up. Still bugs me though. I'd like to be able to get them 100% air free.

 

[Jakobi]

So for reference, my bleed procedure went like this.

Start with PFP adjuster backed right out.
225ml of fluid from the vacuum pump into a measuring jug.
Set the cart in the vise at a 45 degree angle, bleed hole pointed up.
Use same masking tape and cover the bleed hole pointing down.
Shaft extended, pour the fluid down the bottom edge of the cart like you're pouring a beer.
At the same time, stroke the shaft to bleed the oil through the mid valve.
Note: twist the shaft at the same time to allow the bubbles to rise towards the top and create flow through the ports.
Once no more air can be heard/felt through the mid valve, compress the shaft, and set aside.
Repeat for the second cartridge.

Take the first cartridge and mount in the vise the same as step 1.
Compress the shaft into the cart to raise the oil volume.
Insert the base valve so that the valving contacts the oil and rotate to get some fluid into the valve. You should be able to do this without the bottom O-ring seating past the open bleed hole.
Hold the BV, make sure the bleed hole is open, and extend the shaft.
Now push the BV down into the cartridge past the first oring and hold it there.
Stroke the shaft up and you will feel it trying to push the BV back out. Slowly release the BV until the bleed port is just exposed and you will hear it vent.
Note: the o-ring should just allow it to vent as the shaft bottoms against the cart.
Rotate the cart up vertically, and with the shaft still compressed, push the BV down into the assembly. It will force the shaft out as the BV drops into the cartridge.
I use the tool, and a 19mm socket and can get above the cart and push directly down using my shoulder and twist/move my body to engage the threads.
Snug up the compression assembly/BV.
Rotate back to 45degrees, with open port facing up and cycle the shaft, but not deep enough to cause the upper o-ring on the ICS piston to blow past the drain holes .
Set aside to allow the cart to rest and repeat for second cart.

Once it has rested, set it up again in the vise.
At this stage, the cart should be overfilled by 15ml. This is what you will use to purge the air from the cart.
Cycle the shaft up deep enough to push the upper ICS oring past the drain port.
You will hear it discharge any air along with the extra oil.
It will take several cycles to remove the excess oil - and the shaft will not bottom out with the cartridge over filled to this extent without first purging some oil.
When set to correct volume the upper O-ring will sit just visible in the bottom of the drain port with the shaft fully compressed.
Follow up with some very fast cycles using the full stroke to see if you can get any last purges as per GMPs post.
Inverting/Shaking the cartridge a few times (without cycling the shaft) may assist in moving any further air into the center of the piston where it can be purged.
Repeat for second cartridge.

When completed both should behave the same way.

 

[Vindicator]

Good post . Next time I service my forks I'll check what you ask .

 

[StuJohnson]

Per Jake's post....

Are you fricking kidding me???

A video of you doing this would be AWESOME!!!


Sent from my iPhone using Tapatalk

 

[Jakobi]

Speaking with Glenn some more, and when getting to the final steps its important to stand the catridge vertically when purging the air and oil (not 45 degrees). For the final purge/bottom out I always stand the cartridge vertically on a piece of pine on the floor, and use my hand to bottom the cartridge as quickly as possible.

Think I might go and try one more, one more time.

 

[n_green]

Speaking with Glenn some more, and when getting to the final steps its important to stand the catridge vertically when purging the air and oil (not 45 degrees). For the final purge/bottom out I always stand the cartridge vertically on a piece of pine on the floor, and use my hand to bottom the cartridge as quickly as possible.



Think I might go and try one more, one more time.

A video would be great.

 

[Jakobi]

I played some more today, but sorry.. No video

The bulk of the twisting and turning is to just help free any air from within the pistons, inconjunction with flow.

Before you insert the BV use a torch and check the fluid. It shouldn't have any bubbles suspended in the fluid. If it does set it aside and wait for them to surface on their own.

With the base of the IFP, it appears that there is potentially 2 areas where air can get trapped. If you look at the piston you'll see that there is a recess where the shaft is in the middle, a stepped area around it, and then a recess around the outer edge. I believe the step is what is causing the issues and allowing air to get trapped around the outer edge. The inner recess vents through the piston when it reaches the tapered section on the shaft (spring compressed). Stroking the shaft quickly until it bottoms will purge the air and excess oil from this inner section, however does nothing to purge air against the outer edge.

There are a few indicators that air may be present here. If you pick up the cart and shake it near your ear you hear oil sloshing around. Note that this could also be any oil thats been purged and is sitting above the ICS piston.

The challenge is to move the air from this areas over into the middle section, and to do that we need to get flow. Either by physically shaking/moving the cart around. I find rotating the cartback towards a 45 degree and then over some more and cycling the shaft can help flow the oil around, then invert it and complete the fast full strokes again. Repeat. You may find that the cart purges a little more each time. Also take note of the position of the oring on the piston in relation to the port on the side of the cartridge. The aim is to get the o-ring as low as possible where it is only just visible.

Ideally, when completely bled you should be able to change the PFP adjustment and see no change in the height of the ICS piston when the shaft is completely bottomed. You should be able to shake the cartridge around and hear no sloshing/movement of fluid, and if its really good you should be able to flip the cartridge upside down and cycle it without hearing an air gurgling.

Previously I noted that if you continued to cycle the shaft that it would self bleed itself back. Not entirely so. It just distributes the air through the oil so no more gurgling is heard. Comparing this to a well bled cart shows much less damping (noticably fast rebound), for the same given settings (c/r/pfp)

 

[Simmo737]

Your spot on jake, turned it over, gurgle, turned it back, fast compress, touch more air, very firm bleed. Nice!!

 

[Jakobi]

I'd like to look at machining a relief into the base of the piston to allow the outer edge to move the air into the center so it can be purged via the ICS shaft. No sure how much material is there to work with though before hitting seals etc.

 

[wence]

Precisely what myself and my suspension bloke were saying also.
There needs to be a relief as the shaft is too long to reach the indent .
Cheers Mark

 

[Jakobi]

What you mean Mark? Can you elaborate some more? I'm picking up Natos forks in the morning and will put them on my bike for a test ride. They're still running the stock springs, and have been massaged by the same place that installed your gold valves. I believe they have machined the actual shaft to assist in purging via the center of the piston which is what I think your tuner may be talking about also.

I think you can get a good purge through the shaft center, but the design of the underside of the piston leaves an area around the outer edge that traps air. Did you have your tuner do the inversion after bleeding? I'm wondering if you still have some air in the carts and as you work them harder they begin to cavitate/foam up reducing your damping.

When cold I notice they have significantly more stiction too.

Nato and myself are both getting .44 springs and SKF seals in ours.

 

[n_green]

I'll be interested to see how much better the skf seals work for you. That's one thing I don't like about the forks so far, there is a lot of stiction on the outers.
One more ride on mine to get a good grasp of what needs doing and then I'll be pulling them down and taking the challenge.

 

[Jakobi]

See if you can measure the free play (if any) on the ICS spring as well. Seems to be some variation getting around between bikes.

 

[wence]

Jake,
Yes we spoke about cutting a slot into the shaft to allow the trapped air to escape as the current setup will not allow the forks to reset.
I think my tuner is talking about slotting the rod inside the pfp where the rod steps in , to aid in releasing and resetting the build up of pressure.
Should I pull the forks and try and bleed them again ?
Not sure how to go about releasing air in the forks.
I did talk to him about the sloshing around of oil to be heard and he reckons that is normal on cc forks.
He said they are very similar to kyb but have a few issues with the release of pressure .
Cheers Mark

 

[Jakobi]

I've over filled the carts before, and they always self settle at the same volume once bled correctly. This fluid (and any air) is most certainly displaced/purged through the center of the piston/shaft recess. Once they reach that volume they will not force the piston up any higher/purge anymore unless fluid is forced past the lower shaft seal (which can happen when bottoming once fully assembled).

By further recessing the ICS shaft you may be able to purge more oil/air faster or more aggressively in the initial stokes after reassembling the cart, but it still relies on the air being in the center recess of the piston in order to be purged. The holes in the side of the cart which you can view the piston come up into when compressing are used to 'drain' the oil once purged through the recessed shaft. No oil/air is actually purged through these holes.

IMO if oil can be heard sloshing within the cart, there still has to be some air in there (or its oil above the piston that has not been drained). I noticed the sloshing sounds myself which kind of spurred on the further investigation. Even with it like that the shaft would compress all the way and return to full extension on its own, but inverting the cart and cycling made it very clear that there was still air in the system. In the end I couldn't get them 100% purged as they are, but they are a damn lot better than my first attempt of assembling by the book.

If you can slosh it a bit, and then rest it up right you may find you can move some air up under the piston, then repeat the 'fast and hard' bottoming of the shaft and you may experience a further purge of air and notice the piston drop a little further (upper o-ring position when visible through the side drain hole, while fully compress). With a solid bleed only the very top edge of the o-ring recess will be visible at the bottom of the drain hole.

 

[Jakobi]

Serviced my forks again over the weekend. Had a fair bit of contamination come out of one of the inner carts (and a little sludge out of the same outer). Not very promising, but after complete disassembly and pull down I couldn't locate any source/signs of wear/damage. Flushed everything out and reassembled. Hopefully won't experience the same again. I had installed new springs prior to this service so hoping it may have been some break in from that which has built in the bottom of the outer and been forced into the cart where it appears much worse due to a smaller volume of oil.

Back on the bleeding method

Overfill the cart using 225ml of fluid, bleed to best of ability, follow the rest of the advice re dropping the base valve in and snugging it down.

Turn the fork upside down, then back up right. Don't stroke it while upside down. Once upright again, compress the rod slowly until the piston purges. At this point release the rod and allow it to extend.

Repeat above. Turning it over will allow air to move back towards the valve stack, and flipping it back allows more of it to come back into the middle of the piston where it can be purged. The overfill gives volume to achieve around 4 purges before you finish off with one final high speed purge. Each time flipping the cart over and purging again you'll hear discharge of air and oil. While flipping it I was draining any purged oil out from above the piston.

 

[wence]

You are getting me keen to swap the oil in mine again.
I have done Hattah , Finke and another whooped out 4hr enduro since they were last done, plus other rides.
Probably a total of 15 hours of real harsh stuff and another ten of normal riding.
What weight and type of oil are you using again mate?
Cheers Mark

 

[Jakobi]

I'm using 5 wt Amsoil Shock Therapy. Its 15.9cSt@40. Pretty light, but similar viscosity to the Motorex 5wt that a lot of the other big names use. I've been happy with how it holds up in the shocks as well as my previous forks.

 

[n_green]

How are you finding the forks Jake? You don't seem to have re-valved it, so does that mean you are happy with them?

After a fair few hours (15) on my suspension I'm going to take it back to the tuner and have the HSC beefed up both ends, one thing I did wrong was get it re-valved before it had bed in, now the suspension has bed in everything has softened right up and whilst the clickers have taken care of that on the LSC and LSR side of things the HSC is far too soft now.

 

[Jakobi]

Thats odd that the HSC is low on yours. RTs stacks are much firmer than what I am running. I actually changed my BV valving when I just had them apart. Reintroduced a bleed valve and beefed up the HSC to give a plusher ride in the slow going but keep a nice firm bottoming resistance. I find the comp clicker quite sensitive in that if I come in from say 17 clicks it really firms up too much initially, and further out it becomes rather divey under brakes. I'd also like to know to what extent the PFP effects the rebound.

IMO, your best way of increasing HSC is to just tighten up the float a bit on the MV.