I'm studying the reversing gear plans for the Stuart 10V, and although I understand the Stephenson gear (I think), I can't see what the range of steam admission is. I thought one set the eccentric at 90 degrees to the TDC, either side to run in either direction. The 10V eccentrics appear to be pinned with max throw's (lobes?) at 120 degrees apart. The drawing then goes on to say that the "eccentrics are set at 30 degrees advance".
So what is the range of advance (for forward and for reverse) for the eccentrics?
I had expected an eccentric to be 90 decrees out of TDC.