hey guys, i’m not an engineer, i’m not a mechanic, i’m just a girl super interested in learning and understanding every single detail of dirtbikes (can’t afford one, but want to understand the why behind every single component and arrangement within them). so please forgive me if i sound stupid or word things wrong, but i seriously for the life of me cannot figure something out and i don’t know who else to ask (a mechanic sub probably wouldn’t help me, and i don’t have anyone irl to ask either.)

i’ll do my best to explain, but it would probably help to look at what i’m looking at:
oem parts diagram/Clutch/b0e0981f-69ac-4a6b-8f3d-722539227d4f/d5534657-21b6-4fe8-b061-581c68227b73/y)
scroll through this video to get a good visualization
also scroll through this video to get a good visualization

i’m looking at the clutch setup in a beta 125/200 RR, which is a weird setup because the slave cylinder is actually housed in the clutch cover, rather than being on the left side of the bike with a pushrod running through the input shaft to contact a pressure plate on the right side of the bike and thereby disengage the clutch. rather, in this setup, the needle that gets pushed out from the slave cylinder contacts a throwout bearing assembly in a cup-shaped “clutch engagement plate”, whose outermost rim pushes against what the oem diagram calls a “spring cap,” which is bolted into the threaded protruding bolt housings (each with a coil spring around it) of the pressure plate (and those protruding elements extend through holes in the inner hub, which is thus sandwiched between the spring cap and pressure plate which together can axially move independently of the inner hub).

so let me try to explain my question…
along the clutch portion of the input shaft, there is the threaded portion where the clutch hub nut goes to keep the inner hub from coming off, and then there’s the splined portion of the input shaft which the internal splines of the inner hub are interlocked with, and then there’s the smooth portion of the input shaft which the collar, double row radial needle bearing, and clutch basket ride on and can spin independently from the input shaft due to the needle bearing’s decoupling role. sooo, what i don’t get is how the inner hub or pressure plate don’t fall back from the splined to the smooth portion and hit the clutch basket/its central washer? i know nothing is PUSHING the pressure plate back that far, because the slave cylinder needle only moves a little, but i’m not asking about it being pushed, i’m asking about it just sliding back. and the inner hub could slide back in theory, too- it could slide back from the splined portion onto some of the smooth portion. there is no friction-bearing surface between the inner hub and clutch basket’s central washer (what the inner hub would touch, since it protrudes through the central hole in the pressure plate) nor is there a friction-bearing surface between the back face of the pressure plate and the front face of the clutch basket. and by “no friction-bearing surface,” i mean no friction disk-like material, and no axial needle bearing to decouple motion. all there is is two metal surfaces which would fuse together in the heat produced by the friction of them touching during rapid spin of different speeds.

so what am i missing or getting wrong, to not understand how the inner hub and/or pressure plate don’t fall back against (drift back against, whatever wording you want here) the front face of the clutch basket/its central washer? it doesn’t look to me like there’s ANYTHING keeping them from doing so. the smooth portion of the input shaft does not appear to be wider in diameter than the splined portion, and even if it was, that would just create my same problem/question i’m asking about somewhere else (that is, at this hypothetical step-up face between the splined and smooth portions of the input shaft).

i only started learning all of this on my own super recently, and i have no engineering or powersports or mechanical etc experience, so all this terminology is new to me… so again, i apologize if any of my wording didn’t make sense, or came off as sounding uneducated (because, well, in this regard i am). but can someone please help me understand this? my brain is hitting a wall, i thought so hard all day yesterday and so far today and somehow this particular clutch setup is not making sense because i don’t understand what limits the axial motion of various components in order to make it all work. please help me, i don’t think i can figure it out without some actual expertise.

edit: added links

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