I have a 1250 Cub that I got from someone that had just had the K301 engine rebuilt. It runs fine but it shakes like mad. Took the engine out and found that the engine builder had removed the balance gears and it has the crankshaft with the flat spots on the balance throws. I have an opportunity to get a set of used balance gears but the person has no idea what hp K series they came out of. Were the balance gears all the same? Or different depending upon the hp? Having the engine internally balanced is an expensive option that I would rather not have to do. Thanks.