CrowSeph

Hello. I need to replace the bearings from the BMC crd351 hubs.
basically after I removed the cassette I can see on the right side a text with the direction for loosing it.
But when I try with the wrench the left side spins too. On my mavic wheel set those cap are easy to remove, just by grabbing it and pull toward me with bare hands. The others crd seems to have some sort of special way.
​​​​​​a friend suggested to grab and keep it still with some plumber wrench and then screw the right side but honestly seems quite brutal since the wrench may ruins the cap itself
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Duragrouch

I don't know anything about that hub, but do not use a pipe wrench or channellocks on it, you'll ruin it. Do some research to find the correct way, don't mess with it until you do. Many manufacturers of nearly everything these days, post online PDFs with operating instructions and sometimes also maintenance manuals. Go look.

FBinNY 

I did a very quick search and found this exploded view.

If that looks familiar, it seems to use a spring ball on the left, and set screw to lock the right.

Either way, mentally translate the image to your hub and see if that guides you.

If I found a different hub, my surefire search process is "xyx hub exploded view". I find these most helpful because I process better visually than via text

Duragrouch

(above) Wow, you got better eyes than me, I can't see either of those things, but I trust ya, you tend to know your stuff on these things. If I'm seeing things right, I find it interesting that the bearing arrangement looks more similar to an old freewheel hub, the right bearing at the right hub flange, than a freehub with the right bearing just inside the freehub end, closer to the right dropout. I guess with thru-axles being much larger diameter, you can get away with the larger axle bending moment of that.

FBinNY 

Actually, my eyes ain't so good. The set screw in the tiny image I was viewing turned out to be an arrowhead.

In any case, thr right side is screwed on, with wrench flats provided. If the maker were at all diligent, there would be a way to hold the axle, otherwise why have wrench flats.

So, I'd look for an internal hex or similar feature on the left side.
If not, I'd improvise avwsy to hold the axle without the risk of damage or distortion.
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As for the design, this is becoming very common, and what I call a "motor/machine" system. The freehub body is a simple rotor on 2 bearings, with the wheel hub having its own bearings. The clutch is between them, rather than in either module.

The separation of load points from chain tension and axle weight makes it very different from a classic freewheel design, and axle breakage isn't an issue.

CrowSeph

The exploded view is correct, but there isn't any ball bearing on left side. Just two holes. Probably those holes have a key role for the disassembly...

FBinNY 

So, stick something through them, and use that to hold the axle while turning the other end off.

CrowSeph

Ive tried with an Allen key but there is no way to keep it still

FBinNY 

Make an axle vise with 2 blocks of hardwood, or aluminum.

Clamp them together in a vise, separated by a thin strip of similar material. Drill through to the same diameter as the axle. Separate, remove the shim and you can now hold the axle without damaging it.

If you have decent hand skill, you can simply wrap the axle with paperv or a rag, stick a pin into the holes, and hold gently with pliers with the pin preventing it from turning.

Duragrouch

That sounds like a good system, because the freehub ratchet or clutch would be out in the open and serviceable, versus original freehub designs. Not sure I'd want it on a loaded touring bike with old (small) axle diameters, but with a large thru-axle, absolutely. Even possible to service in the field. OOO! I think it also means that in the field with a drive-side broken spoke, you don't need HG lockring tool, wrench, chain whip to replace spoke, you just remove wheel, remove axle and separate freehub and wheel hub, replace spoke, reverse. If true, that's smart, and simple.