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.
i concur final timing in each direction should be done independently. with some of Stuart’s reverse sheaves where a single casting is used for both I find one direction can be tuned to work perfectly and the other direction is always rough. So I always use two sheaves.
I thinks it’s a case of minor inaccuracies adding up, port size, position, valve dimensions, eccentric throw etc.
i spend most of my time fixing badly running or non working engines and no two are the same, even Stuart machined ones. So I treat them as hand built mechanisms and machine to fit rather than drawings.
i have worked on 4 Victorias and 1 twinVictoria, none of them had the crosshead running correctly in the guides. Also I don’t think any of the parts were interchangeable Whilst most appeared well machined.
The eccentrics should be set to 90 degrees each side of TDC. When you set the timing, you want steam admission to start before the piston makes it to TDC to help “cushion“ the piston as it reaches TDC. Im guessing the 30 degrees you speak of is when the steam port just starts to open and not its TDC. If you do the math, that will bring the two eccentrics at 120 degrees apart at the time the steam port starts opening. In Keiths videos, he always starts at 90 degrees and then does a final adjustment by ear.