I have been pulling my hair for the past few weeks..

I got this set up with a Paso clutch, the cover is brand new and is the lightened racing tipe fitted on F1 and 851 Strada; the Master cylinder is from a 999

I got a new slave piston , seal and bearing and mad the bronze pin on the lathe.

The issues I have are:

1- somehow air is getting inside in the system, I though the slave piston could be spinning around, but I made markings on it and cover to double check and it stays exactly where it is, so the issue is elsewhere,

2- the clutch seems to be fine when cold, shortly after the engine starts heating the MC feels like there is air in the system, I open the bleeder on the MC and after two”pumps” it goes back to normal , so there is definitively air in the system.

3- after I start the engine I can hear the clutch quote noisy like screatching and when I check the inside of the cover around the piston and push plate are dusted by very fine bronze dust... il seems like the bearing is seizing, but it not , it is fairly new ita has only 75 road miles , with lab/garage time probably 3-4 hours overall.

I did make a different bronze pin and things are a little better but far from perfect and air is still getting in

Not sure what to do....earlier today I took everything apart and re-checked but I can’t find anything wrong.

Any suggestions?

Maybe all the air is not expelled during bleeding , they are a proper bitch to bleed . I usually push the fluid up from the slave to the mc. Also pays to dismount the mc so as to orient it so bubbles dont get trapped around the bango fitting on the mc.

The bronze pin may wear down to the shape of the pressure plate if its surface isn't straight and flat.
How much space is in the piston, behind the bearing? If the pin was made longer than the bearing is wide, could it touch the inner bottom of the piston?

I see your points but ... no...

the MCs have a bleeder on them, so any air trapped can get out.

I bleed the MC, it works percectly for 5 -10 minutes then air gets in from somewhere; I know this Clutsh is notoriously difficult, but theoretically you should see there is an issue straight away, not only after the engine is warm.

I will see if by heating the cover with an hair drier makes any trapped air "go up" but it should be noticeale that there is air trapped even then cold..... it is not like the air stops being compressible at 15 degrees and becomes compressible at 50; yes the T does have some influence but not for this kind of temperatures.

Still puzzled

The Bronze pin... I have two, one following the drawinds you can find online and one I made with few differences (a little bit thicker on the mushroom , edges rounded and a small copper washer under it so it works better against the bearing.)

The pin is just 1mm longer but there is plenty of space behind so it is not touching the bottom of the slave.

I bough an overhauling kit for the MC, but it is not leaking so I find difficult for air to go in if fluid cannot go out, then maybe I am not grasping the intricacies of the hydraulic circuits...

Its possible that the outer most seal ( some call it the rear seal ) in the mc is leaking , but when they fail it usually allows air to be sucked in as the lever is compressed and then when lever is released that air is then pushed past the piston and into the "working pressure area " ( the rear seal will allow air to be drawn in as lever compressed but not out as lever released ) , it may well not leak a drop of fluid.

just a brief update

I got the overhaul kit for the 999 MCs, ythe job id esasy and intuitive despite the "147-different-languages-with-weird-pictures-and-microscopic-writing" leaflet.

it took around 30 minutes to do the job and another 30 minutes to do the bleeding. I went for a ride and the clutch is much better, no air is getting in and it works fine.

as for the noses, they got worse... now I have a cat being strangled in the clutch. I recheched the pin and i found brass dust again, wich make me think that either the material is wrong or there is somethoing else that is not right.

I took off the pressure plate and made sure all springs were sat correctly. Before reinstalling it I polished the contact area tring to smooth any markings so that the plate does not "engage" with the Brass pin. One thing i note ths that the old piston had a much bigger contact area where the pin pushes the plate so I wonder it that might be a reason .

The opther thing is the bearing, are they specific or that is just a standard sealed bearing? I dont recall where I got that from.

Skate board bearings , I made my brass mushroom out of an 8mm brass bolt , just thinned down the head a bit and chopped shank to length( width of bearing )

I would check the springs unsprung length to make sure they are even . I get the feeling that when compressed the pressure plate is tilting slightly , some paso pressure plates had a spigot that fitted into the end of the input shaft but I dunno just how effective it was . Probly also pay to check clutch plates for warping

Dunno how well it would wear , and teflon gives off poisonous gas when machined so safety 1st........get some other mug to do it

I posted the problem on the F1/TT facebook page and one of the members suggested that the thrust bearing could be the bad .

I then went to check the bearing size on this wonderful site and I learned it is a 608-2Z , so "just because", despite knowing mine is sort of new, I decided to get one and I discover that the 608-2Z is available in 2 versions...

a)ceramic bearings
b)steel bearings.

now considering the way the bearing works (as a thrust bearing) I wonder if there might be an issue using the ceramic over the Steel type....

Anyway I ordered a SKF 608-2Z 3.73£ steel version and will check if that sorts my clutch out .

Don't ask what I have on, it was brand new but I don't really remember the type, knowing me I might have put the ceramic "just because it sounds funky"

will update shortly .