Shup, I posted on here somewhere that a single cylinder Continental gocart racing engine had a flywheel on the cam shaft to prevent tortional impulses caused by the valve springs from thrashing and in turn destroying the timing gears. Many people mistakenly think that big Saitos vibrate a lot but are mistaking tortional impulses caused by the engines light weight and strong power pulses for vibration. For example, I put my Old high compression Saito 150 on a Sullivan DynaMount and as you stated above, at speed it moved very little but at idle and just above the rocker arm cover end of the engine moved a lot, too much to suit me. My Saito 100 moves very little and my YS .91FZ hardly at all. The prop driver end of all three does not move at all, at least not that you can see. I could go on here because I love to try and check things out but this is long enough.