It's been bit quiet, because my lathe's belt snapped. It's now fixed, so back to project.
It seems that my lathe is seriously underpowered, what comes to that 50x50mm alu piece. Machining it is even more tedious, than I expected

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I looked an alternative for solid crankcase, and found out, that the Hoglet type would be much easier to achieve. Being scratch built part, it suits the spirit of this project

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Two small bars are 20mm(0.787") SS 2172, that is available nearby store

. It machines quite well, so I use them for cylinder liners.