This engine doesn't have an internal balancer or use a dampner on the front like most. Some of these engines simply vibrate a lot and there is little or nothing that can be done about it. Unless you want to spend a the money to get the engine balanced in a professional shop that is equipped for such work. If your engine is one those that vibrates a lot the excessive vibration can contribute to crank breakage. To help the vibration at idle you may want to increase the idle speed a little to smooth it out. However, this will not do anything for the vibration in the next vibration cycle at a higher speed. As for the converter, it is cheaper to just replace it. Is your crank breaking on the front or the rear? We have had some of these pass thru our shop, however, we have not had any with broken cranks as a result of the vibration. Most of the time the vibration is just an aggravation to the operator.