Hello Cobja and Norm
I can't answer the first question.
These are non-de-compressed engines.
Maybe there is simple 'good' compression.

The flywheel system is proprietary.
The nut releases the taper lock but not the flywheel.
A soft mallet should ensue ...

Help here: -
https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/103091/villiers-g-series-engines.html

Hope this helps.
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Jack