Okay..........I've made a decision (drum roll).
After watching my Vidhata very carefully while running, I've come to the conclusion that any vibration is being caused by the base that I built. It was never intended as a permanent solution, just something I could roll the engine around on while playing with it. I've already described it in another post, and frankly, when sitting on the casters it only has four small points of contact with the floor. Any slight springiness in the frame compounds the tendency to vibrate up and down. When sitting on certain level spots on the garage floor it doesn't bounce......just sits there making electricity. Get one of those casters in a low spot and the tendency to hop a bit kicks in.
As I also mentioned before, the engine appears to be quite well balanced and I think I'm letting my imagination get away with me when I start to worry about "ultra balance". It runs just about as nice as 38ac's in his videos AFTER balancing. Sometimes a guy can get lucky!
So, I'm going to frame up a box on top of my garage floor, measuring 4.5 feet long by 3 feet wide and 10 inches deep. According to an online calculator, that works out to a minimal weight of 1496 lbs. worth of concrete, and I might make it 12 inches deep....1995 lbs. Before pouring, the surface will be cleaned and one of those horse mats cut to fit in the bottom of the box. A rebar cross hatch will be installed about three inches up from the mat and the hold down bolts (3/4 inch by 16 inch) will be anchored with the ends bent under the rebar. There will be eight bolts, two on either side of the existing frame cross members. The concrete will be poured around the rebar/bolts and leveled. Several days will be allowed for curing and the engine/generator assembly lowered on top with my fork lift. Steel wedges will be placed under the cross members to keep the frame level, about 1/2 inch above the concrete, and then a rich sand/cement slurry poured in, forced under the cross members and leveled. After that cures for at least a week or more, steel cross straps (3/4 inch by 2 inch) will be placed over the bolts so that each frame cross member is pulled down firmly....a "four grunt" tightening sequence.
This arrangement has several benefits....
1.) Mass......what the Lister book calls for
2.) Serviceability......the entire engine/generator package can be removed and fork lifted out if necessary.
3.) Height......cranking will be a no stoop exercise and all components can be reached from a standing position.
4.) No permanent change to the existing floor. The entire block can be fork lifted out if necessary by running chains through the bolts.
Opinions? Suggestions? Laughter?