as Locozodiac says its pressed together around the bearings.
This is common practice, particularly on 2-stroke engines for outboards, motorcycles etc, but unfortunatly means you need a serious press to take it apart and put it back together again. Of course it needs to be put back together in a jig to get all the angles etc correct.
It can be done, I once did an RD350YPVS Yamaha twin myself when I had access to a 5tn press, but I'd not recommend it.
The guys who do it all the time don't take too long as the jigs etc make the job easy, so the labour charge isn't too steep.
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