Chapmans disease is also a common builder ultralight pilot condition!
What I thought was my original A12GX bottom end was even lighter than another stock front
dizzie A12 bottom end I had. I gave both away to another 1000 enthusiast and kindly called
me to see if I wanted it back as it had a knife edged crankshaft, 124mm H rods and custom
flat top pistons (27mm comp height). Never clicked it was way lighter than another stock A12.

The A14 bottom end felt almost 60% heavier in comparison and was a 2 person job versus
this worked A12 bottom end which was an easy 1 person lift.
Come to think of it the bores at 77mm removes like 4 x 3mm thick steel pipes as well
but still the difference was night and day in weight with the stock a12.