The I beam frame is pretty light , It does have some rubber mounts , which do a good job of reducing the transfer of the engine vibration to the framd.. And yes it is a vibration, in the horizontal plane with the cylinder.. when running at 2200 rPM it moves about 1/8 inch each stroke. for some viscious movement, so anything that is not heavy cast and absolutely attached securely will vibrate loose, sheetmetal attachments fatigue really quickly. Thus the fuel tank and the radiator dieing so soon. I will admit that I am a bit concerned about longevity of some other parts ie fuel lines etc but so far so good.
Steve