Was the flywheel run ning smooth beforetaking away all the material?Then You can balance it. If it isreally out of center, that would be really bad!Dont be too hard to Your machinist!It is almost impossible to take away materialfrom a balanced flywheel without the need torebalance it afterwards.It is also almostimpossible to put it onto a lathe and have itperfectly centered there.You will at first have to put a shaft into the lathe, and bring it to 1,125". Dont release it! then put Youradapter onto the shaft and check if it is centered. if not, "clean" the surface a little bit. Eventually You will have to create anew center fitting for the flywheel.Now mount the flywheel to the adapter andcheck on the clutch-side if it is running round now. (if it fits, never disassemblethis again!)If all this fits perfect now, you shouldbalance the flywheel including the adapter.(i normally put some cleaned ball-bearings into the hole to do this)At last fix the pressure plate to theflywheel and check balance again.Dont rip out the clutch!changing gears is not funny without clutch!Serial wound motors need changing gears!a 9" motor wants to do about 1500 to 3500rpm, 11" about 1000 to 2500-3000 Torque and efficiency decrease significant on higher revs!