For a stock 750 Commando (CR 9:1)the calculated combustion chamber volume works out as 46.5 cc. For a stock 850 emgine (CR 8.5:1) this will be 55.2 cc
As stated by the above posting, there are several variations. The only reliable way to verify the combustion chamber volume is by holding the engine in a position with the spark plug hole uppermost, and pour liquid in the cylinderhead with a burette.
Sorry I do not know the answer to the second part of your question.
Peter. 1974 Commando 850 1972 Trident T150T 1961 Goldie DBD34 1969 Benelli 250 sport special
If you are doing accurate calcs of chamber volume for compresh, with the head off the engine, you must measure. Make a plexi cover for the head that's sealed with grease on the edges with a hole in the middle and fill the chamber with water. I use a low cost 60cc medical syringe vs a messy/expensive burett to acurately measure the water needed to fill the chamber.
The largest variable to deal with when calculating static compression is accurately measuring the volume of your piston crown. I have a proven accurate procedure used by engine builders for many years. I will Email a copy. Ask.
Doing these heads is a pain, since I have to pull the head studs to get the domed acrylic disc to seat over the chamber. The 850 measured 50cc almost on the money. This RH10 head might not be a full depth chamber. The 68-70 06-0380 750 is original but had a little carbon in the chamber and on the valves and also read 50CC. You may get further variation on top of that due to different valve head profiles.
dynodave BSA 3 1961-1963 Ducati 3 1992-2002 Norton many 1951-1975 87 Serv-Equip 100HP MC brake dynamometer,