I dynamically balancd mine. Removed the head and crankcase door and spun the crank, flywheels, piston and rod up as close as I could get to the 650
RPM running speed and adjusted counterweights on the wheels untill the movement of the frame was at a minimum(under .005" for-aft) the whole assembly, engine, generator and frame were up on 3/4" pipe rollers and I could easilly move the 1000# of weight with the tip of a finger. I re-assembed the engine after balance and while it was still on the rollers, ran it with 2KW of electrical load on the generator. For-aft movement was about .010"-.015". It will be bolted to a 1300# block of concrete, but it runs happily under 3KW load just setting on my garage floor.