Cheers Bill. nothing in that new drawing looks difficult to change. If you're satisfied with the config you've illustrated I'll get to it soon.
This is gold Bill, I've been wondering about exactly this for a while but wasn't sure if there was an issue. It definitely didn't sit right with me that the valve gear were working out of sync with the pistons. I'm at work now so I can't dig in to this but if you're willing I might ask for more help with this when I'm ready to tackle it?Hi Cian. I slowed the video settings down to watch the valve gear and noticed that at the moment the 4 sets are running in unison rather than in step with their own cylinder. I don't know easy it is to adjust the motion relationships in your software but this is something we went over on the old TRMA site. At that time I wrote out the motion for the cranks and valve eccentrics as follows.
On both engines, for forward the reverser handle is pushed outboard and the top of the crankshaft rotates to outboard, ie the same direction the handle moved. This also fits the engines having opposite rotation. The reverser's valve rod and piston rod will be moved downward and the eccentric links will be pushed outboard. The inboard eccentric rods will be the ones that are pushing on the valve stems.
The HP and IP cylinders are inside admission (steam supply is to the middle of the valve piston) and have crossed rods (the two eccentric rods look crossed when the crank is away from the piston). Looking at the engine drawings with the HP in forward I measured 52 degrees lag behind the crank for the eccentric whose rod is on the valve stem and 54.5 degrees lead for the other eccentric. I'll use the same as a guess for the IP.
The LP cylinders are outside admission and open rods but as a result have the eccentrics rotated 180 degrees. Continuing with my guess that makes the lag/valve stem eccentric 232 degrees behind the crank and the lead one 234.5 degrees ahead. In reverse the 54.5 and 234.5 degree lead eccentrics will be lagging and will be the ones pushing on the valve stems. Confused? me too!
The last bit is that in forward the lag/valve stem eccentric in each pair is the one that is away from the LP's and towards the HP or IP. They show on the drawings as being the ones whose rods are vertically straight, no offset. I think the object is to clear the bearings and couplings on the crankshaft without adding length. It also means that forward's dominance of the working hours pushes on the straight rod rather than the offset one.
The inside/outside admission and crossed/uncrossed rods are design decisions that one would not normally realize the designer had to consider but they do have a trickledown effect on finalizing the valve gear. It would be interesting to explore old texts about the advantages of each.
Back to our video, stick a protractor on the front end of the port crankshaft and set it so that a stationary pointer at the top touches zero degrees when the HP is on TDC. Use a protractor scale that has the numbers increasing CCW around the disk so that the degree reading increases as the crank progresses through a rotation. The protractor on the starboard engine will have a CW scale.
The degree events on the two protractors will then be (in order along the crankshaft, valve term valid for forward operation):
View attachment 111144
The same events on the mirrored protractors means that the two cranks and their eccentrics are assembled with an opposite rotation of features around the shaft. I think that your having mirrored the engines will inherently accomplish this.