Jameslow, bro the oz tz.12 have the bearings issue, I ran 2 of those engines, one stock and other EBMOD, both were great engines and run like hell! but the bearings went to fast. With the engine stock for months is one thing but running, you should replace both bearings asap, before it begins to suck air and lean(that happens to me with the first TZ I ran), A good choice are Boca Bearing High speed stainless steel bearings, I put those bearings on my IDM Evo2 and was an exelent choice!!!
Byron's Racing Fuels/Airtronics