Hi guys ,
is the main shaft pressed into the bearing on the round plate of a mc21 dryclutch gearbox ?

They can be a bit tight sometimes.
Generally, they should just slide in and out easily. Ooh-er missus!

The worst sticking one I've ever encountered was on a gearbox that looked like it had been run low on oil. The bearing and shaft looked like they'd got a bit hot.

MC21 gearboxes are the same ratio-wise for wet or dry clutch set-ups.

Normally, on all racing bikes, the mainshaft slides easily out of the bearing holder
though I have dismantled a few nsr250 gearboxes for inspection and all of them had the mainshaft stuck.
Renewing the bearings didn't helped, #800 wet & dry sandpaper didn't helped as well.

I suspect that lack of lubrication and poorly maintenance e.g worn bearings, lead them to this condition though I can't really tell for sure.
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2t-racelab.com

I used to spin my shaft up in the lathe and give it a bit of a dress up with some wet & dry so that it slid in and out perfectly. Nothing worse that having to hit my shaft with a mallet while trying to swap cogs in the paddock.