I tried to find out maintenance and operation manuals of the Limbach L275 engine.

Does anyone have these docs?

I am also looking for the crankshaft thread dimensions and type on the prop hub side. If somebody has it, I would be happy if he can share this data with me.

Have a nice day.

Norbert.

Georg Vogelsang from Germany had one on a very large WW1 bipe at the QSAA many years ago....The're still used on ultralights. There are pictures on the Limbach website, so you could probably contact the factory...
I have one here to be used on a giant scale P51 race plane...Mine is new, but has no prop hub or carbs...
The internal thread on the crank looks like 8mm x 1.25....the tag on the case says 22 HP, 7200 rpm...