I bought a running 149,backed it off my trailer and made it 100yds before the eng threw the rod. I tore it down,sent block,crank,head,and valves to local shop for repairs. Block-.010, crank-.010,vales -OK justed lapped, and head shaved .010 to clean up. Upon assembly I felt the balance gears were a little loose. I had read several places that they did not make much difference and could leave them out. I was building a stock 3600rpm eng for yard work but decided to install new bearings and reinstall them. I purchased bearings an carefully pressed them into the gears and they would not go onto the shafts. I found out that their were 2 different p/n's for the bearings and useing the wrong one would not allow them to fit the shaft.So I assembled the eng without the balance gears. I put eng in the frame and upon startup I could not believe the vibration.It is severe.My 109 runs real smooth, but the K321 is really bad.As luck would have it the PO of the 109 left the starter/generator pulley loosen up to the point that the pto shaft and keyway are shot.I have a K301 that uses a lot of oil,but the shaft is good, so I figured to rebuild it and replace the eng in the 109. I just opened that up yesterday and found the balance gears to be much looser on the shaft than the ones in the K321. That started me thinking. I believe the statements made concerning not needing the balance gears was made in reference to a K301 and not a K321.I would like to reduce the vibration in the 14hp and I'm not sure if I should reinstall the gears in the 12hp replacement for my 109 machine. ALL comments wellcome.